Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

General Astronomy >> Beginners Forum

Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | (show all)
rsimpkins
super member


Reged: 04/11/14

Loc: Lehi, UT
Achromats & Apochromats - Cutting Past The Hype
      #6485901 - 04/24/14 03:43 PM

I was at a star party recently and I got to look through two refractors made by Explore Scientific. One was a ES127CF 5" f/7.5 ED triplet refractor. The other was a AR127 5" f/6.5 achromatic doublet refractor. Both were pointed at Jupiter in semi-*BLEEP* seeing that was keeping both scopes at lower powers. In the doublet I noticed a deep violet color fringing effect dancing around Jupiter that, quite frankly, was rather annoying (at least to me). The triplet was rock solid and looked great. Really, really great.

I've read that acromats are prone to this violet color effect, something that apochromats apparently fix. What's the actual non-BS take on this? If one wants to avoid the violet blues, do they have to step up to a more expensive triplet? Or is it possible to get no-color views through the "right" achromat in the "right" configuration?

I know the answer is probably really complex. I've read a few articles on this subject that break out all these complex graphs and complicated scientific explanations. I'm searching for a simpler "usually right" answer. If someone ponied up the extra $$$$ to get an apochromat, do they get views that generally avoid the violet effect?

It would really be lame to spend $2500+ on an apochromat only to find out that the purple star eater is still there. Might as well buy a much cheaper achromat and learn to live with it. Thoughts?


Post Extras: Print Post   Remind Me!   Notify Moderator  
GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6485915 - 04/24/14 03:53 PM

You'd need a very long 5 inch achromat to avoid chromatic abberation.

Even the best achromats cannot eliminate all the CA. And it gets worse the larger the scope is. A 60mm achromat may be free of color if around F10+ ... a 5 inch one would need to be super long. There are charts for that.

Still, on other objects like DSOs, it's not as important visually. So that scope pointed on M13 may be just fine.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Abhat
sage
*****

Reged: 12/14/13

Loc: Middletown, MD
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6485932 - 04/24/14 04:01 PM

There is no doubt APOs reduce fringing dramatically or might also eliminate it. Also slow achromats (F/8 and beyond) reduce fringing. I have heard that F/11 achromats virtually eliminate fringing and 4" versions are available for about $500. Using fringe killer or light yellow filter, the fringing can be brought under control. Whether that reduction is acceptable or not is up to individual and his or her taste for tolerance of such kind of fringing.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Mark9473
Postmaster
*****

Reged: 07/21/05

Loc: 51°N 4°E
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: GOLGO13]
      #6485946 - 04/24/14 04:08 PM

Quote:

You'd need a very long 5 inch achromat to avoid chromatic abberation.



I wouldn't consider anything shorter than f/20 in that size. I had a 90 mm Vixen achromat that was f/14.4 and on Jupiter the purple haze still bothered me.


Quote:

on other objects like DSOs, it's not as important visually. So that scope pointed on M13 may be just fine.



Yes, but...
The apo will put more light into the airy disk and give tighter stars. The net effect on something like M13 is that a smaller apo will go as deep as a larger achro.

When I sold my 90 mm achromat I bought an 80 mm apo. I was a bit nervous about giving up light grasp and resolution. My first views on Jupiter and M13 immediately made it clear that I had in fact upgraded and not just downsized. Both these targets looked at least as good, if not better.


Post Extras: Print Post   Remind Me!   Notify Moderator  
jrcrillyAdministrator
Refractor wienie no more
*****

Reged: 04/30/03

Loc: NE Ohio
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Abhat]
      #6485951 - 04/24/14 04:11 PM

Two rules of thumb for achromats. To bring the violet halos down to a level that one can ignore if sufficiently motivated - an F ratio about three times the aperture in inches or use very low magnifications (10X per inch or so). To bring the halos down to where they won't be noticed at reasonable magnifications - an F ratio of five times the aperture in inches. You can't say what F ratio will work unless you know the aperture.

ED doublets using FPL53 can do a pretty good job at an F ratio around two times the aperture in inches.


Post Extras: Print Post   Remind Me!   Notify Moderator  
EJN
Carpal Tunnel
*****

Reged: 11/01/05

Loc: 53 miles west of Venus
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: GOLGO13]
      #6485953 - 04/24/14 04:12 PM

By the Sidgwick criterion a 5" achromat would need to be at least f/15. By the
Conrady criterion at least f/25.


Post Extras: Print Post   Remind Me!   Notify Moderator  
obin robinson
Carpal Tunnel
*****

Reged: 10/25/12

Loc: League City, TX
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6485961 - 04/24/14 04:15 PM

Quote:

It would really be lame to spend $2500+ on an apochromat only to find out that the purple star eater is still there. Might as well buy a much cheaper achromat and learn to live with it. Thoughts?




Try a minus violet filter. They work wonders. I was blown away by how much of a difference they make. I use one for imaging on my ST-80 and it really tames the violet down to apo-like levels. White stars look more white rather than a sharp blue/violet.

obin


Post Extras: Print Post   Remind Me!   Notify Moderator  
spencerj
Pooh-Bah
*****

Reged: 11/17/04

Loc: Londonderry, NH
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: obin robinson]
      #6485983 - 04/24/14 04:24 PM

Quote:


Try a minus violet filter. They work wonders. I was blown away by how much of a difference they make. I use one for imaging on my ST-80 and it really tames the violet down to apo-like levels. White stars look more white rather than a sharp blue/violet.

obin




The issue is that the purple fringe in the achro is unfocused light. Sure you can block that light with a filter so that you do not see it, but it is still unfocused light that is not making it to the final image. More focused light = a better final image. TANSTAFL


Post Extras: Print Post   Remind Me!   Notify Moderator  
REC
Post Laureate
*****

Reged: 10/20/10

Loc: NC
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: EJN]
      #6485989 - 04/24/14 04:28 PM

Hmmm, I was just doing that last night. I had out my 80ED f7.5 600mm and my 102 f9.8, 1000mm scope for some general viewing as it was a nice night. On Jupiter with both scopes at 100x they where pretty close. A little CA for sure, but not really bad vs. the 80ED with the FPL53 glass element. I could see three belts pretty well in both. With a Baader moon and skyglow filter in the 102 achro, it was not bad.

Over at M35 star cluster, both scopes showed nice sharp stars and the CA was not much of an issue. Same thing on M42 and the larger aperture did show it a little better.

No real big comparisons, as I said, just out for some casual viewing. I use both of these scopes as my Grab n Go when I don't want to set up my larger scopes.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Abhat
sage
*****

Reged: 12/14/13

Loc: Middletown, MD
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: spencerj]
      #6486006 - 04/24/14 04:36 PM

Quote:

The issue is that the purple fringe in the achro is unfocused light. Sure you can block that light with a filter so that you do not see it, but it is still unfocused light that is not making it to the final image. More focused light = a better final image. TANSTAFL




Does it mean that a 5 inch Achromat with Semi APO filter will work like a 4" APO after assuming 20% loss of light blocked by the filter? Or the image quality would still be bad as that spectrum of light is lost?

5" Achro is substantially cheaper than 4" APO.

Edited by Abhat (04/24/14 04:44 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
EJN
Carpal Tunnel
*****

Reged: 11/01/05

Loc: 53 miles west of Venus
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6486026 - 04/24/14 04:47 PM

Quote:

It would really be lame to spend $2500+ on an apochromat only to find out that the purple star eater is still there. Might as well buy a much cheaper achromat and learn to live with it. Thoughts?




My thought is just get a Newtonian, you can get much more aperture for
the money and zero color. If you get a premium mirror like Zambuto it
will eat a smaller apo.


Post Extras: Print Post   Remind Me!   Notify Moderator  
StarStuff1
Post Laureate
*****

Reged: 04/01/07

Loc: South of the Mason-Dixon Line
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: REC]
      #6486041 - 04/24/14 04:53 PM

Years ago I had a very nice 4.5-in f/12.5 refractor with a Fraunhoffer (sp?) achro objective. I was very happy with it until one night a guy set up next to me at a star party with a "small" 102mm f/9 scope. It blew me away with the contrast and color purity on Saturn. A few months later I had a copy of that same APO, a Celestron C/102f (fluorite). The achro was sold.

APOs cost less today that in the past. My C102/f tube alone cost nearly $2500 new. I paid about $1550 used. Today a good APO in that size can be had for less than that.

Still, achros can be great values today. As mentioned, filters can help if color fringing is objectionable. They can be stopped down for really bright objects such as the Moon and bright planets. What would Galileo have given for a modern 4-in f/10 achro?


Post Extras: Print Post   Remind Me!   Notify Moderator  
RussL
Music Maker
*****

Reged: 03/18/08

Loc: Cayce and Lancaster, SC
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Abhat]
      #6486047 - 04/24/14 04:55 PM

I get better images in my 80ED doublet (f7.5) than in my 120 achro (f5) at the same mag with the same eyepiece. CA is much more reduced. That's on bright objects. On dim object either scope performs well.

Post Extras: Print Post   Remind Me!   Notify Moderator  
David PavlichAdministrator
Transmographied
*****

Reged: 05/18/05

Loc: Mandeville, LA USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6486101 - 04/24/14 05:22 PM

I have a 4" Stellarvue f11 achromat and with a Baader fringe killer, Jupiter looks very nice!

David


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Abhat]
      #6486102 - 04/24/14 05:23 PM

Quote:

Quote:

The issue is that the purple fringe in the achro is unfocused light. Sure you can block that light with a filter so that you do not see it, but it is still unfocused light that is not making it to the final image. More focused light = a better final image. TANSTAFL




Does it mean that a 5 inch Achromat with Semi APO filter will work like a 4" APO after assuming 20% loss of light blocked by the filter? Or the image quality would still be bad as that spectrum of light is lost?

5" Achro is substantially cheaper than 4" APO.




The short answer to your question is that no, a filter will not magically turn a 5 inch achromat into an 4 inch apochromat. The issue is defocused light, that the different colors do not come to focus at the same place. A filter can help make the image more aesthetically pleasing by removing some of the defocused light but in my experience the views are not comparable to crisp, clean views that good quality ED doublet or triplet provides.

In general, one can say that the slower the focal ratio, the better the color correction and the smaller the aperture, the better color correction. A small long focal ratio achromat, say a 60mm F/13, there is very little false color. On the other hand, as the original poster discovered, a 127mm F/6.5 achromat shows a considerable amount of false color.

One rule of thumb people use is called the Chromatic Ratio. The CR is equal to the focal length divided by the aperture as measured in inches. As John Crilly mentioned, a CR of three is viable at higher magnifications, a CR of 5 is almost apo like.

The two scopes mentioned above, the 60mm F/13 and the 127mm F/6.5 have CR's of 5.6 and 1.3. As one would expect, the 60mm is almost color free, the 127mm is quite colorful.

I have several refractors, two that make an interesting comparison are TeleVue NP-101, it's a 4 inch F/5.4 apo that has 4 elements and is corrected for field curvature as false color, coma and astigmatism. New, one of these will set you back close to $4000. The other is an Orion 100mm F/6 achromat, for what it is, for what it cost new, (about $200), it's a good, solid telescope.

I enjoy them both and both provide decent quality, enjoyable views. At low magnifications, the better quality optics and flat field of view mean the NP-101 does provide sharper, cleaner views but the biggest difference is at high magnifications. The false color of the 4 inch achromat with it's CR of 1.6 limits it ability to resolve close double stars as well as show crisp, contrasty views of the planets. In my experience, filters make the image somewhat more aesthetically pleasing but do not greatly improve the resolution or the contrast.

There is a lot to know about the color correction in refractors, the different ED glasses, the focal ratios and apertures and how it all plays out. If that 100mm refractor was F/15, things would have been different, much less false color but it would have been about 60 inches long..

The bottom line is that Rsimpkins had it right, he saw what he saw and that is what one would expect to see.

Jon Isaacs


Post Extras: Print Post   Remind Me!   Notify Moderator  
Mr. Mike
Pooh-Bah
*****

Reged: 11/08/05

Loc: Churchville, NY
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6486214 - 04/24/14 06:07 PM

What about high-end doublets like the Takahashi Flourite model? Is that a color-free scope? It had better be for the price!

My SV110 does show some violet fringing on the planets but tight focus calms it way down and for whatever reason I get nothing color-wise on the moon. As for DSOs like star clusters & galaxies? I see no issues with a good quality doublet.

Realistically, it costs a TON of money for what is essentially violet color reduction on planets & perhaps slightly better performance on DSOs but Id question how much. At our next star party, Im gonna try and look through a high end APO(of similar aperture & eyepiece) at some bright globular and see how much better it really is than my SV110mm.

I think the rule of thumb for this hobby is: As you spend more, the differences between the quality of the products and views gets smaller and smaller. Like I said - you pay dearly for that last small percentage of color correction & small contrast bump. Lets realize though that a cheap, faster achromat is going to be pretty *BLEEP*.

Either way - I WILL have a Takahashi triplet someday.

Edited by Mr. Mike (04/24/14 06:32 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Widespread
professor emeritus


Reged: 05/11/11

Loc: Bowling Green, Kentucky
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6486224 - 04/24/14 06:12 PM

I don't know about 5 inch versus 4 inch, but my 4 inch F/9.8 achro can show just a bit more than my 90mm F/7 apo on most targets. Yes, the color is less pristine than the apo, but there is a tiny bit more detail, and the lesser field curvature and long FL make for pleasing views and easy focusing.

That's a $60 scope beating a $1300 scope (barely). But when it comes to mechanicals and the joy of usage, the SV wins hands down. On a manual altaz, it's very easy to reach the slow motion controls with the apo, and it's small and light enough to ride easily on my little SLT GoTo mount.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Dave Lee
sage


Reged: 02/14/13

Loc: Pinehurst, NC USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Abhat]
      #6486240 - 04/24/14 06:22 PM

Quote:

Quote:

The issue is that the purple fringe in the achro is unfocused light. Sure you can block that light with a filter so that you do not see it, but it is still unfocused light that is not making it to the final image. More focused light = a better final image. TANSTAFL




Does it mean that a 5 inch Achromat with Semi APO filter will work like a 4" APO after assuming 20% loss of light blocked by the filter? Or the image quality would still be bad as that spectrum of light is lost?

5" Achro is substantially cheaper than 4" APO.




Two things going on here (although they are really the same thing).

1) The color fringing that was reported and found objectionable. You can filter this out (for the most part).

2) All those 'fringey colors' that created a halo are 'visual information' that has been lost, even when you filter out the fringing. This information is unfocused and unviewable. Or put another way if Jupiter's Great Red Spot was the Great Purple Spot it would be invisible (pretty much) through a achromat with a typical Semi-Apo filter.

#2 is where the APO's of the world generate views that are inherently better than achromats at manageable focal lengths. But this does not mean that the achromats of the world can't generate very good viewing experiences.

dave


Post Extras: Print Post   Remind Me!   Notify Moderator  
lamplight
Carpal Tunnel
*****

Reged: 09/18/12

Loc: western MA, U.S.
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Dave Lee]
      #6486894 - 04/25/14 12:01 AM

when i was looking to upgrade my achromat refractor i basically just read lots and lots of user reviews keeping my eyes peeled for color issues in the reviews.. i asked the same question here as lots of people do, and i frankly didn't understand much of the really technical discussion that this thread doesn't have

in my case i came across some reviews of a certain series of scopes made by orion (and another manufacturer i think, but basically the same scope/glass) that was getting great reviews as an extremely well corrected doublet ED with the good glass (FPL53). based on price thats what i went with.. as far as CA it was a HUGE upgrade.. very little color on the brighter objects.. i haven't used it in a while so i can't give a good description as others here have on specific objects, which should be helpful as thats exactly what it sounds like you were looking for.... so.. "cutting past the hype" is pretty simple: how do YOU enjoy the views? if you can get to a local astro club chances are there are always some refractors to look through. from what i can see there are some good doublets out there that are VERY close to triplet APO's as far as color goes. i understand "very" might be subjective depending on the visual acuity of the viewer.. anyhow, mines pretty fast too (120mm f/7.5), so its quite surprising to me. like i said, i have no idea how its done, but i can see a HUGE difference over your average achro

i do understand Jon's and others' descriptions of how the different wavelengths of light come to focus at different points in a refractor.. as i recall there are three (?) colors that come to focus at different points, so if the purple is one of them, would that equate to 1/3 (or whatever the equivalent is) loss of light gathering if using a filter to remove it?

Edited by lamplight (04/25/14 12:14 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
lamplight
Carpal Tunnel
*****

Reged: 09/18/12

Loc: western MA, U.S.
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: lamplight]
      #6486916 - 04/25/14 12:12 AM

heres a monster thread to confuse the &%$# out of you on doublet vs triplet APO's. i don't mean to complicate the issue especially as i just mentioned how confusing it all is even to me.. but i wanted to point out one thing that has stuck out to me in my research: there are some smoking good doublets out there. they're almost as expensive as some triplets for good ones it seems. You can thank me later for the added confusion

Post Extras: Print Post   Remind Me!   Notify Moderator  
gunfighter48
sage
*****

Reged: 03/18/13

Loc: Mill Creek, Washington
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: lamplight]
      #6487020 - 04/25/14 02:11 AM

A tale of two refractors.

My C102GT on Jupiter showed purple fringe around the planet. There was also purple in the bands and polar caps of Jupiter. On the moon there was slight purple and sometimes greenish/yellow fringe around the moon depending on the eyepiece used.

Using my ES AR152 on Jupiter there was slight purple fringe around Jupiter but NO color on the planet. Using it on the moon there was less purple fringing than the C102GT. There was also some greenish/yellow fringing depending on the eyepiece used. The fringing is better controlled in the AR152 than in the Celestron C102GT.

According to all that I've read and been told, the fringing should have been worse in the AR152. But the opposite is true. Theory is fine but often runs into trouble in the real world. Some of us are not bothered or just don't see the fringing that other folks see. The fringing in both of my refractors is not a deal breaker for me. The C102 shows some spectacular views of clusters! I haven't had the chance to look at clusters in the AR152 yet.


Post Extras: Print Post   Remind Me!   Notify Moderator  
jgraham
Postmaster
*****

Reged: 12/02/04

Loc: Miami Valley Astronomical Soci...
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: gunfighter48]
      #6487216 - 04/25/14 07:29 AM

I own several refractors from my little 40mm Copyscope all the way up to my biggo LXD75 AR-6 and the degree to which I notice the purple fringing varies quite a bit and not just between scopes, but between objects and sky conditions. Most of the time I don't notice it at all or that it is so slight it doesn't bother me. If it does, I'll install a Baader semi-Apo filter. No, it doesn't turn an achro into a Apo, but it does a nice job of reducing the purple fringinging and also serves as an effective light pollution filter. A few nights ago we had a rare evening of exceptional seeing and I just happened to have my AR-6 out for observing double stars. I was not using my semi-Apo filter and I has my best view of Mars ever and there wasn't even a hint of purple fringing even at 290x. When I take pictures with my AR-6 the fringing is always there and the filter is a big help. Visually, it comes'n goes.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Dave Lee
sage


Reged: 02/14/13

Loc: Pinehurst, NC USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: lamplight]
      #6487224 - 04/25/14 07:35 AM

Quote:



SNIP

as i recall there are three (?) colors that come to focus at different points, so if the purple is one of them, would that equate to 1/3 (or whatever the equivalent is) loss of light gathering if using a filter to remove it?




In theory it could. But in practice most likely not.

1) Not all 'targets are the same' in terms of their color content. This is particularly true for targets such as emission nebula.

2) The eye is far less sensitive to deep red and violet (the unfocused colors in most achromats these days) vs. the red to blue-green range that is typically focused.

So in practice, no.

dave


Post Extras: Print Post   Remind Me!   Notify Moderator  
Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: spencerj]
      #6487226 - 04/25/14 07:38 AM

Quote:

Quote:


Try a minus violet filter. They work wonders. I was blown away by how much of a difference they make. I use one for imaging on my ST-80 and it really tames the violet down to apo-like levels. White stars look more white rather than a sharp blue/violet.

obin




The issue is that the purple fringe in the achro is unfocused light. Sure you can block that light with a filter so that you do not see it, but it is still unfocused light that is not making it to the final image. More focused light = a better final image. TANSTAFL




I don't entirely agree. The violet light is really not good for much -- the image is simply better without it.

The real problem isn't the violet -- the most obvious manifestation of chromatic aberration -- but all the other colors that do continue to make it through a minus-V filter. They continue to focus at different points, blurring the image.

If you don't mind viewing the Moon in false color, an aggressive color filter will reduce the blur even more. But as everyone says, you still can't turn a 5-inch f/6.5 achromat into a 5-inch f/6.5 apochromat -- or a 5-inch f/20 achromat -- using filters.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: lamplight]
      #6487233 - 04/25/14 07:47 AM

Quote:

as i recall there are three (?) colors that come to focus at different points, so if the purple is one of them, would that equate to 1/3 (or whatever the equivalent is) loss of light gathering if using a filter to remove it?




The purple is not a primary color. Purple is a combination of the defocused red and violet light, the ends of the spectrum.

While one might think of light as being composed of separate colors, it is in fact a continuous spectrum so if one eliminates part of the spectrum that is most bothersome there still remains unfocused light.

Using single color filters is possible but one is potentially eliminating details.

Newtonians and reflectors are free of chromatic aberration but has issues of their own.

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
Mark MacKenzie
member


Reged: 04/14/14

Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6487276 - 04/25/14 08:19 AM

So here's my beginner first post....
What if I stop down that achromat? My 4" f9 shows some violet on Jupiter. What if I had a stop in front of the objective to make it a 3" f12? Or a 2.4" f15?
Bad idea or not? I haven't tried it yet.
Mark


Post Extras: Print Post   Remind Me!   Notify Moderator  
Vondragonnoggin
Post Laureate
*****

Reged: 02/21/10

Loc: Southern CA, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6487278 - 04/25/14 08:20 AM

I don't know why these conversations don't go hand in hand, but there is always someone asking about which filters to buy for astronomy use and usual answers consist of UHC, OIII, H-Beta, or the like and everyone gets happy about the thought of getting a little MORE detail out of nebula viewing.

Mention achromat and filtering it out like with Longpass, or semi-apo, or minus V and suddenly people are worried and discussing how much LESS detail is seen.

Really. Make up your minds about it because you confuse people by emphasizing the lost information and exaggerating its effects. If you want the most information, it's simple - buy an apochromat or reflector.

If you want to get by on a budget with a doublet Fraunhofer design, then just put a filter on it if you find chromatic aberration objectionable or buy one with long enough focal length that the colors are all focused, or just view with it as is if you think it's alright.

There is generally too much exaggeration about detrimental effects when talking about achromats, yet consistently heavy filtering is recommended to get the most detail out of some objects. Even those with reflectors tend to like using contrast enhancers like the Baader Moon and Skyglow and will talk in a thread about it being a contrast enhancer rather than the typical detrimental loss of color information as described with an achromat.

In both instances of filtering, it is removing information. Just as heavy narrowband nebula filters remove a ton of visual spectrum information

People are okey dokey with one application and always whining about the other and it makes little sense to me.


Post Extras: Print Post   Remind Me!   Notify Moderator  
REC
Post Laureate
*****

Reged: 10/20/10

Loc: NC
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Vondragonnoggin]
      #6487300 - 04/25/14 08:39 AM

Just an FYI to add to this post. I used a Baader Moon & Skyglow filter on my C102gt and it really cleans up Jupiter and the moon. Also I use a nebula filter on it and it really provides a nice view of M42.

Also, the Magazine, Astronomy Technology Today just did a review of the 4 popular Baader Anti-Fringing filters and the one they picked wit the most pleasant view on Achro,s was the Contrast-Booster.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Vondragonnoggin
Post Laureate
*****

Reged: 02/21/10

Loc: Southern CA, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Vondragonnoggin]
      #6487312 - 04/25/14 08:44 AM

I really think to stop all the hand wringing, fretting , and general terror of lost information that these debates evoke, that people should educate themselves in the visual spectrum and typical object spectrum emission along with more detrimental spectrum emission such as sodium, mercury, and the like that we generally filter out if around sources that interfere with object lines of emission. Know what is being cut and what is not, what is irrelevant to the eyeball (human visual spectrum sensitivity) and what is not. What can be isolated and even in some cases amplified to get greater detail or to lose information purposefully with spectrum lines that are heavily overpowering less strong spectrum lines with good information.

A class in filtering on its own by experimentation is expensive to start with , but can be very useful and filters can be sold later to get some money back, but generally if one wants to research it, there is a ton of information about human visible spectrum and the varying degrees even that physiology of the sometimes unique nature can make people sensitive to.


Post Extras: Print Post   Remind Me!   Notify Moderator  
lamplight
Carpal Tunnel
*****

Reged: 09/18/12

Loc: western MA, U.S.
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Vondragonnoggin]
      #6487341 - 04/25/14 09:03 AM

Isn't the goal different though? Gaining some contrast by removing some very specific areas of the spectrum vs achro concerns of gaining sharper focus , a brighter image, AND more potential contrast? The affected targets being totally different as well, it's kind of different issues yet from one perspective the same.. Filtering out some visible light. It seems the amount filtered out between the two issues is surely different amounts depending on target. Probably people get concerned about achro filtering light loss because we're talking about relatively bright/close objects and cutting out larger chunks of visible light that a better design wouldn't have to sacrifice. With the right nebulae and the right associated filter, the light loss is usually 100% acceptable and helpful, in the ranges affected. Right? That's just my interpretation of the facts subject To change due to information gained.

Post Extras: Print Post   Remind Me!   Notify Moderator  
David PavlichAdministrator
Transmographied
*****

Reged: 05/18/05

Loc: Mandeville, LA USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Mark MacKenzie]
      #6487351 - 04/25/14 09:10 AM

Quote:

So here's my beginner first post....
What if I stop down that achromat? My 4" f9 shows some violet on Jupiter. What if I had a stop in front of the objective to make it a 3" f12? Or a 2.4" f15?
Bad idea or not? I haven't tried it yet.
Mark




Welcome to Cloudy Nights! Interesting question!

David


Post Extras: Print Post   Remind Me!   Notify Moderator  
spencerj
Pooh-Bah
*****

Reged: 11/17/04

Loc: Londonderry, NH
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Vondragonnoggin]
      #6487361 - 04/25/14 09:14 AM

Quote:


I don't know why these conversations don't go hand in hand, but there is always someone asking about which filters to buy for astronomy use and usual answers consist of UHC, OIII, H-Beta, or the like and everyone gets happy about the thought of getting a little MORE detail out of nebula viewing.

Mention achromat and filtering it out like with Longpass, or semi-apo, or minus V and suddenly people are worried and discussing how much LESS detail is seen.

Really. Make up your minds about it because you confuse people by emphasizing the lost information and exaggerating its effects. If you want the most information, it's simple - buy an apochromat or reflector.





Very few things in this existence are black and white. To pass the time we talk about the various shades of gray. If you talk about anything long enough, the subtle differences become exaggerated.

Acrhomat refractors can be spectacular visual instruments. They can also be dogs. The quality of the telescope design and the optics matter. Filtering has its place. Using a specialty filter to tease out fine detail in an object is a reasonable thing to do--even though you are blocking out other information.

If every topic had exactly one right answer, then the forums would have a lot fewer posts.


Post Extras: Print Post   Remind Me!   Notify Moderator  
jrcrillyAdministrator
Refractor wienie no more
*****

Reged: 04/30/03

Loc: NE Ohio
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Mark MacKenzie]
      #6487390 - 04/25/14 09:27 AM

Quote:

So here's my beginner first post....
What if I stop down that achromat? My 4" f9 shows some violet on Jupiter. What if I had a stop in front of the objective to make it a 3" f12? Or a 2.4" f15?
Bad idea or not? I haven't tried it yet.
Mark




Sure. That's a time-honored method of taming false color in fast achromats. You lose liught gathering and resolution, but you gain color control.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon_Doh
scholastic sledgehammer


Reged: 09/16/11

Loc: On a receiver's back
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: David Pavlich]
      #6487396 - 04/25/14 09:32 AM

Not all achros are equal from my experience. Every one of those Celestron 102's that I've looked through have had a huge amount of CA. But the ES achros vary from scope to scope. On Jupiter the AR 152 that I viewed it through showed a thin dark band of purple. You really had to be looking for it to see it because it blended in with the dark background of the sky. The planet showed no CA. Same with the moon. Bright stars and M13 were fine. To me the stars focused tightly and showed nice color.

So, I would look through an achro like this one and think all the negative things about acrhos are over blown. Then I would look through one of those Celestron achros and the CA was so bad it almost blinded me.


Post Extras: Print Post   Remind Me!   Notify Moderator  
howard929
Member
*****

Reged: 01/02/11

Loc: Low End of High Ground
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: spencerj]
      #6487398 - 04/25/14 09:33 AM

I feel that David K. says it best in his tag line that goes something like: If your not having fun with this hobby, your brain is broken and it's causing you to do it all wrong... or words to that effect.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Vondragonnoggin
Post Laureate
*****

Reged: 02/21/10

Loc: Southern CA, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: lamplight]
      #6487407 - 04/25/14 09:38 AM

Quote:

Isn't the goal different though? Gaining some contrast by removing some very specific areas of the spectrum vs achro concerns of gaining sharper focus , a brighter image, AND more potential contrast? The affected targets being totally different as well, it's kind of different issues yet from one perspective the same.. Filtering out some visible light. It seems the amount filtered out between the two issues is surely different amounts depending on target. Probably people get concerned about achro filtering light loss because we're talking about relatively bright/close objects and cutting out larger chunks of visible light that a better design wouldn't have to sacrifice. With the right nebulae and the right associated filter, the light loss is usually 100% acceptable and helpful, in the ranges affected. Right? That's just my interpretation of the facts subject To change due to information gained.




That's because the focus usually gets immediately steered to planetary observations (brightest objects). As I said, examine the filter curves of the contrast boosting Moon and Skyglow filter realizing its a popular filter even in reflectors for teasing out details in planetary observations. It also has some heavy cuts in various ares of the visible and IR spectrum.

Pound for pound and inch for inch, if getting the most information is your goal, the reflector remains top dog in larger apertures. Central obstructions cause slight loss in contrast so in smaller sizes, budget aside, the apochromat is probably the best bet for maximum visual information with less contrast loss. Bigger sizes tend to be less easily mounted, handled, afforded by average consumer, etc. so reflectors make sense.

The achromat offers the general populace, access to unobstructed views but with caveat that it doesn't concentrate all colors to focus equally.

My achromat is not a planetary instrument personally. I like it for DSO's and less bright targets at lower powers. I like my reflector for planetary, but with the Baader Moon and Skyglow filter enhancing contrast (and losing some visual information too).

My point was really that someone new to getting all this information, might worry unnecessarily about loss of info and think they either must get a reflector or an apochromat to get a decent view. The best idea is to just take a look if possible, through others scopes and try to get a sampling of reflector, achromat, and apochromat, rather than reading through a lot of subjective information on detrimental effects and causing worry as it gets built up to some bogeyman levels in threads like these.

Filtering is good in my opinion. In a lot of cases it can entirely enhance the viewing experience. One can save for highest quality views in a refractor or a reflector (such as a premium optic mirror), but during that period of saving, just get out and enjoy what you can use. The information can sometimes be subtle in what is lost at filtering but huge in the thread talking about it.

Good luck to all and enjoy the scopes you have and save for ones you want.



Post Extras: Print Post   Remind Me!   Notify Moderator  
Mark Costello
Post Laureate
*****

Reged: 03/08/05

Loc: Matthews, NC, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Vondragonnoggin]
      #6487411 - 04/25/14 09:39 AM

I had my achro rig out last night for a little over an hour, spending 30 minutes apiece on two targets. The last one was M44. The session with it included a main sketch at 27X, then adding extra details at 49X, 69X, and 118X. The interesting thing is that with each hike in power, more stars came into view. The hike from 27X to 49X brought the most stars, about 15 extra stars, into view.

But it was the first object that gets closer to the discussion into the forum. The first object was Jupiter. I guess the "achro-is-dead-don't-waste-your-money-on-one-because-it's-good-only-for-stuff-like-M44" bunch would say that was a waste, but what the hey, the ES AR127 is my only scope. And it didn't look like a waste to me. The 5 minute view at 118X showed some hints of thin banding in both polar regions so up we went to 236X to do the sketching. That showed some interesting shadings and whorls in the two main tropical bands (the winds there must make our hurricane look like soft breezes) and yes, there appeared some whitish strips inside the polar caps: one in the south cap and a couple in the north cap. Again, some interesting wind patterns evidently are in there.

My experience with Jupiter and the moon is pretty much as gunfighter48's with his ES AR152. There is a deep and soft purple haze around Jupiter but the shadings on the disk are cream and brownish gray, and not so yellow. There is a thin purple halo over the rim of the moon's image but when I'm observing the lunar landscapes head-on, I just don't see the evidence of chromatic aberration.

If I was starting over again now, m-a-b-y-e I would have gotten a smaller ED refractor. But except for participating in threads like this (I occasionally do but not often), I don't think about it. After all, my 5" achro is here and doing everything I ask of it. I don't have the urge to replace it with an ED. Oh, I'm hoping to get a genuine apo some day to supplement my refractor, the kind that works with mirrors.

Edited by Mark Costello (04/25/14 09:40 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Dave Lee
sage


Reged: 02/14/13

Loc: Pinehurst, NC USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Vondragonnoggin]
      #6487440 - 04/25/14 09:55 AM

Quote:

I don't know why these conversations don't go hand in hand, but there is always someone asking about which filters to buy for astronomy use and usual answers consist of UHC, OIII, H-Beta, or the like and everyone gets happy about the thought of getting a little MORE detail out of nebula viewing.

Mention achromat and filtering it out like with Longpass, or semi-apo, or minus V and suddenly people are worried and discussing how much LESS detail is seen.

Really. Make up your minds about it because you confuse people by emphasizing the lost information and exaggerating its effects. If you want the most information, it's simple - buy an apochromat or reflector.

If you want to get by on a budget with a doublet Fraunhofer design, then just put a filter on it if you find chromatic aberration objectionable or buy one with long enough focal length that the colors are all focused, or just view with it as is if you think it's alright.

There is generally too much exaggeration about detrimental effects when talking about achromats, yet consistently heavy filtering is recommended to get the most detail out of some objects. Even those with reflectors tend to like using contrast enhancers like the Baader Moon and Skyglow and will talk in a thread about it being a contrast enhancer rather than the typical detrimental loss of color information as described with an achromat.

In both instances of filtering, it is removing information. Just as heavy narrowband nebula filters remove a ton of visual spectrum information

People are okey dokey with one application and always whining about the other and it makes little sense to me.




While I don't totally disagree with the quoted above, the 'longpass/Apo filter' application vs. UHC/OIII/etc applications really are quite different.

In one (UHC/OIII/etc) the 'information of interest' is very specifically in a couple of quite narrow bands. Excluding 'the rest of it' is for almost every application FOR THESE OBJECTS perceived as a good thing (note that I did say almost.

In the achromat case in general, the issue is WAY/WAY more broad. IMHO they are not equivalent things - not unrelated but really not the same. Sometimes the 'color free viewing' of whatever benefits from some kind of filtering and sometimes not. In my mind this is not the same as dealing with chromatic aberrations across the board.

But I would agree that the information available across the internet on achromat vs. APO (pick your APO definition now) issue is confusing and not always accurate.

dave


Post Extras: Print Post   Remind Me!   Notify Moderator  
Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Mark MacKenzie]
      #6487472 - 04/25/14 10:13 AM

Quote:

So here's my beginner first post....
What if I stop down that achromat? My 4" f9 shows some violet on Jupiter. What if I had a stop in front of the objective to make it a 3" f12? Or a 2.4" f15?




Stopping down the objective will greatly reduce the false color -- and also greatly reduce the amount of detail you can see. It may be worth it if your goal is strictly aesthetic. It's definitely not worth it if your goal is to see as much planetary detail as possible.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Vondragonnoggin]
      #6487492 - 04/25/14 10:25 AM

Quote:

I don't know why these conversations don't go hand in hand, but there is always someone asking about which filters to buy for astronomy use and usual answers consist of UHC, OIII, H-Beta, or the like and everyone gets happy about the thought of getting a little MORE detail out of nebula viewing.

Mention achromat and filtering it out like with Longpass, or semi-apo, or minus V and suddenly people are worried and discussing how much LESS detail is seen.

Really. Make up your minds about it because you confuse people by emphasizing the lost information and exaggerating its effects. If you want the most information, it's simple - buy an apochromat or reflector.




Sorry, but there's an excellent reason that the two discussions don't go hand-in-hand. It's because they have nothing -- zip zero -- in common.

Filtering to reduce chromatic aberration with a minus-V is a matter of compensating for an equipment defect. It does not reduce detail -- in fact, it increases it. However, it does not increase it as much as using an inherently color-free instrument in the first place.

Mind you, all of this is secondary to aperture. My 4-inch f/6 achromat shows hideous color fringes around planets, but it still shows a lot more planetary detail than a 60-mm APO. Likewise, the main reason to use reflectors isn't that they're color-free (though they are), but because they have much bigger apertures than refractors of similar cost.

But even when using reflectors, serious planetary observers often use color filters. This isn't to compensate for any defect in the instrument, but rather to eliminate light coming from the object itself. If you want to view the Great Red Spot, eliminating the blue light will increase the signal-to-noise ratio and improve the image. This is a case where less is more for a strictly scientific, information-theoretical reason.

Likewise with nebula filters. When you want to observe an emission nebula that glows primarily in the O III bands, eliminating other wavelengths improves the signal-to-noise ratio and allows you to see more detail.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Abhat
sage
*****

Reged: 12/14/13

Loc: Middletown, MD
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Mark MacKenzie]
      #6487494 - 04/25/14 10:26 AM

The stop down does wonders on very bright objects. I used my ST-80 stopped down exclusively on Venus, Moon and Sun (with filter of course). Especially on moon stopped down St-80 not only sharpens the view but also eliminates need for moon filter and you can view the moon in natural white color. Th excessive boil and shake on Venus calms with the stop down and you can actually analyze the phase and % illumination nicely.

However on Jupiter and Saturn and other less bright objects I lose lot of detail when stopped down and I am better off with full 80mm even with the fringing.

Edited by Abhat (04/25/14 10:31 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Mark Costello]
      #6487511 - 04/25/14 10:36 AM

We certainly should not give the impression that achromats are bad. I had a C102 HD (4 inch F9.8 achromat) and it was an excellent scope and very reasonably priced. Chromatic abberation was a bit annoying and I used a minus violet filter here and there. But it provided great planetary images as well as good images on DSOs.

Nothing wrong with achromats for sure. Especially if cost is of concern. While many folks recommend reflectors because of the bang for the buck. I think a lot of people would also benefit from a 4-5 inch achromat as a first scope. There are benefits to them over reflectors (cool down, collimation usually not needed, etc). This is certainly not a one size fits all hobby.


Post Extras: Print Post   Remind Me!   Notify Moderator  
David PavlichAdministrator
Transmographied
*****

Reged: 05/18/05

Loc: Mandeville, LA USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Mark Costello]
      #6487536 - 04/25/14 10:51 AM

Mark pretty much covers it. One of the best deals in our hobby is the venerable Celestron C6R. Terrific on the big open clusters and enough aperture to go smudge hunting. Yea, it has false color, but at f8, it's not as bad as the faster AR6 class, especially at the CR6 price point. There's a used one in our Classifieds for $350!

You have to keep in mind what you have and know its quirks. And it's always impressive at an outreach to have a C6R on an Atlas with that 8" extension.

David


Post Extras: Print Post   Remind Me!   Notify Moderator  
Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Abhat]
      #6487549 - 04/25/14 11:00 AM

Quote:

The stop down does wonders on very bright objects. I used my ST-80 stopped down exclusively on Venus, Moon and Sun (with filter of course). Especially on moon stopped down St-80 not only sharpens the view but also eliminates need for moon filter and you can view the moon in natural white color.




Those are special cases, for the following reasons:

The Sun can rarely be viewed at high magnification because sunlit ground causes atmospheric instability. So there's relatively little to be lost by throwing away aperture.

There's such a vast amount of detail to be seen on the Moon that even if you do throw away aperture, it still leaves a huge amount of detail remaining. However, if seeing maximum detail on the Moon is your goal, you would do far better to use higher magnifications than to reduce the aperture. This would also eliminate any conceivable need for a Moon filter.

As for Venus, there's essentially zero detail to be seen except for its size and phase. (Unless you are very patient and skilled, observe it daylight, and have ultraviolet-sensitive eyes.) So again, throwing away aperture has little or no cost. Moreover, Venus is the single object in the sky where false color is most obtrusive.


Post Extras: Print Post   Remind Me!   Notify Moderator  
GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: David Pavlich]
      #6487550 - 04/25/14 11:01 AM

I saw that classified David and would love to get it. But my wife would absolutely kill me if I got that puppy! I've looked through one and it was excellent.

Here is a picture of my old C102:



Here is a picture of a C6R mounted on a 30 inch dob



Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Vondragonnoggin]
      #6487565 - 04/25/14 11:10 AM

Quote:

I don't know why these conversations don't go hand in hand, but there is always someone asking about which filters to buy for astronomy use and usual answers consist of UHC, OIII, H-Beta, or the like and everyone gets happy about the thought of getting a little MORE detail out of nebula viewing.

Mention achromat and filtering it out like with Longpass, or semi-apo, or minus V and suddenly people are worried and discussing how much LESS detail is seen.

People are okey dokey with one application and always whining about the other and it makes little sense to me.




It is unfortunate that it does not make sense to you but there are good reasons for these differences. The fundamental difference here is that nebula filters are chosen for enhancing the contrast of a specific object whereas the minus violet filters and such are chosen to limit the chromatic aberration of the telescope. These are two different issues.

-Narrowband filters are very effective for increasing the contrast of a small class of objects which emit light in a very narrow band of the spectrum. The light that comes from many nebulae is the result of the atomic level activity that is most prevalent in the nebulae. The O-III filter is designed to pass the light the results from Doubly Ionized Oxygen.

If an object primarily emits light in the O-III band, then by only allowing the light in that band to pass and blocking all other wave lengths, then the contrast, the difference between the object and the background sky is greatly enhanced. This is not a small difference, it is sufficient to allow me to see considerable detail on the Veil Nebula from my San Diego backyard... A notch filter like this might have a band pass of 10-20 nanometers, with the visual spectrum being about 200 nanometers in width, by blocking the background sky, this can result in an increase in contrast by a factor of 10 or 20..

This is really no different than using your cell phone, listening to your radio, or watching broadcast TV. Each of those depends on very sophisticated narrow band filters to detect a very faint signal from the broad electromagnetic spectrum..

- Filtering the light from an achromat is quite a different problem. You are not trying to match the filter to an object, you are not trying to listen to a specific radio station. Rather, you are trying to make up for the aberrations, the noise added by the telescope optics themselves. Since much of the spectrum is defocused to some extent, trying to filter the worst part of the spectrum can be somewhat helpful but the issues still remain.

One might think a fast focal ratio achromat as a radio that greatly distorts both the bass and the treble but does a half decent job in the mid ranges even though it is not perfect. One can remove the bass and treble but the music, it just not sound the same, information is lost. You can recognize the music, you can enjoy the music, but it definitely not the same as listening to the full spectrum.

I hope this helps explain the differences, in one case a specific filter is being used that matches the emissions of a particular object and in the second case, rather broad band filters are being used to try to make up for significant aberrations in the optics. Very different.


Jon Isaacs


Post Extras: Print Post   Remind Me!   Notify Moderator  
Vondragonnoggin
Post Laureate
*****

Reged: 02/21/10

Loc: Southern CA, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6487586 - 04/25/14 11:21 AM

To both Jon and Tony:

Filtering is the purposeful elimination or reduction in spectrum to bring out detail. Whether filtering to fine tune a frequency or eliminate unfocused light, the intended purpose is to lose information to see more detail.

Tony - you said what I said. I mentioned planetary filtering for detail even in reflectors. Check. I mentioned aperture and reflector cost. Check.

Again - filtering is the purposeful elimination or reduction in certain spectrum to enhance detail. Whether by eliminating bad information from aberrations or by fine tuning a frequency to bring more information that is swamped usually by your needless information (such as narrowband to eliminate unwanted spectrum) it is the same effect on different scales.

But whatever. Of course you two are always correct whether paraphrasing or concentrating on snippets of entire posts.

Same as it ever was here. This is why I stay out of beginners section usually.

Edited by Vondragonnoggin (04/25/14 11:22 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Mark Costello]
      #6487613 - 04/25/14 11:32 AM

Quote:


But it was the first object that gets closer to the discussion into the forum. The first object was Jupiter. I guess the "achro-is-dead-don't-waste-your-money-on-one-because-it's-good-only-for-stuff-like-M44" bunch would say that was a waste, but what the hey, the ES AR127 is my only scope. And it didn't look like a waste to me.






Mark:

Your points are good ones and are similar to my experiences with similar achromats. Fighting chromatic aberration with filters does little good, the views maybe more aesthetically pleasing but I seem to find that little if any is gained in what I see when viewing the planets and it's better to just accept the chromatic aberration as part of life and make the best of it.

Your post also points to the importance of the observer's skill. Over the years, I have come to realize that the most important factor is the observer and not the equipment. You make some remarkable observations with your equipment and such abilities can only come from spending time at the eyepiece and learning how to see everything there is to see.

You also point to the economics of the equation.. mirrors versus lenses. APO refractors are very expensive and of limited aperture. I am glad that I am able to afford some very fine equipment but it wasn't always that way... And even today.. or more appropriately, last night.. it looked promising for the seeing and with both Jupiter and Mars both well positioned, a good night for observing the planets.

After work I had enjoyed watching my granddaughter's Karate lessons and there wasn't time to setup and cooldown my number 1 Planetary scope so I had to choose between my 4 inch apo and my 10 inch Dob. The apo was purchased used for $2000, the 10 inch Dob was purchased used for $240..

It was a no brainer, I wanted the good planetary views, I went with the Dob..

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
coopman
Post Laureate
*****

Reged: 04/23/06

Loc: South Louisiana
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6487669 - 04/25/14 12:02 PM

If you can afford to get an ED or triplet refractor, do it. The cost of buying it only hurts once, and you will benefit from the enjoyment every time you use it.

Post Extras: Print Post   Remind Me!   Notify Moderator  
GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6487681 - 04/25/14 12:11 PM

As Jon points out the used market can really help. Sometimes the costs can be half of a new scope (as in Jon's case). But even used many Apochromats are pretty expensive reletive to other designs.

It think Apos are a good choice for grab and go scopes from 60mm-100mm around F6-F8. Worth having one to compliment a larger scope.


Post Extras: Print Post   Remind Me!   Notify Moderator  
jgraham
Postmaster
*****

Reged: 12/02/04

Loc: Miami Valley Astronomical Soci...
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: David Pavlich]
      #6487722 - 04/25/14 12:29 PM

"...but at f8, it's not as bad as the faster AR6 class..."

Hmmm, the AR6 is also f/8. The ES6s are f/6.5s. I took a hard look at the ES152 before settling on a used AR6. I was concerned about the color in a faster achromat. It turned out okay for me.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Cames
sage


Reged: 08/04/08

Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6487803 - 04/25/14 01:01 PM

Quote:

I've read that acromats are prone to this violet color effect, something that apochromats apparently fix. What's the actual non-BS take on this? If one wants to avoid the violet blues, do they have to step up to a more expensive triplet? Or is it possible to get no-color views through the "right" achromat in the "right" configuration?




If you are up to reading one more article may I suggest one that puts some numbers to an answer to your question: Seeing spots: A Picturesque and Unmathematical Analysis of Achromatic Objecti...
In the article, respected optician and optical designer, Robert Royce, addresses both the degree of secondary spectrum in achromats and ways to minimize it. Also, he touches on the variability in the individual ability to perceive those extraneous colors. His discussion is also useful to help you understand spot diagrams as they relate to the analysis of secondary spectrum.

Perhaps use it as a counterpoint to see if what you are hearing and reading is based on fact or hyperbole.
-------
C


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Vondragonnoggin]
      #6487874 - 04/25/14 01:31 PM

Quote:

Again - filtering is the purposeful elimination or reduction in certain spectrum to enhance detail. Whether by eliminating bad information from aberrations or by fine tuning a frequency to bring more information that is swamped usually by your needless information (such as narrowband to eliminate unwanted spectrum) it is the same effect on different scales.




Well...

I am well aware of the purpose of filters. This is what your wrote:

Quote:

I don't know why these conversations don't go hand in hand, but there is always someone asking about which filters to buy for astronomy use and usual answers consist of UHC, OIII, H-Beta, or the like and everyone gets happy about the thought of getting a little MORE detail out of nebula viewing.

Mention achromat and filtering it out like with Longpass, or semi-apo, or minus V and suddenly people are worried and discussing how much LESS detail is seen.

People are okey dokey with one application and always whining about the other and it makes little sense to me.




You asked the question "why the conversation about filtering achromats and filtering deep sky objects do not go hand in hand."

I spent a considerable amount of time answering your question and explaining why they do not go hand in hand. Both involve the use of filters but the purpose is quite different.

One enhances object itself by only passing the very narrow band that the object itself emits whereas the other attempts to make up for optical deficiencies by discarding otherwise desirable information. I thought the radio analogy was particularly appropriate, with one, you are picking out a faint signal from the broad spectrum, the other, you are attempting to make up for deficiencies in the equipment.. a bad amplifier or fuzzed speaker.

I will also add that your implication that one only sees "a little MORE detail out of nebula viewing" is misleading and incorrect. The reality is that narrow band nebula filters greatly increase the contrast of many nebulae and in many cases allow them to be seen in detail when they would otherwise be invisible. Deep sky filters make huge differences for those objects which they enhance.

On the other hand, it is questionable whether the long pass, Semi-APO and minus violet filters actually enhance the detail seen. In my experience, the difference is primarily aesthetic and does not result in me seeing more details. As Mark does, I look past the purple haze, it is the remaining lack of sharp focus that seems to most affect the what I see.

If one wants to view the planets with an achromat, longer focal lengths, slower focal ratios are better. My goal here is to help folks just starting out understand their choices and what differences those choices make at the eyepiece and in the field. I do not generally recommend someone first starting out invest in an expensive apochromat. But at the same, since the original question was asked, sharing my experiences and understandings of the differences, there is a place for that.

I find the side by side comparison between my 4 inch F/5.4 apochromat and my 100mm F/6 Achromat quite enlightening. As much as I enjoy the achromat, as much as I love the thing, as much as I try different filters, different aperture masks and such, the difference between the two when viewing the planets is still very noticeable, nothing I have found does much in the way of closing the gap. Masking the 100mm achromat to an 80mm F/7.5 and then comparing it to my 80mm F/7 apochromat bears similar results..

Jon Isaacs


Post Extras: Print Post   Remind Me!   Notify Moderator  
Ed Holland
Carpal Tunnel


Reged: 06/16/10

Loc: San Jose, CA and Oxford, UK
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6488001 - 04/25/14 02:23 PM

I have a Celestron C102, a Meade AR5, C8 and Orion Mak 127. No APO refractors for me, I cannot justify the cost, and prefer longer focal lengths. I would not give up the variety of my instruments, it's something that makes observing enjoyable. The Mak and C8 give me colour free views, and lots of detail, especially the C8.

However, if I want a quick setup, rapid thermal settling and pleasing views without concerns for collimation etc., the AR5 or 102 are in the front line. Yes there are purple fringes, possibly also some spherical aberration (both of which change with temperature). But to me, these are good scopes that get used. I find it hard to get annoyed, concerned or disappointed about an instrument that is still providing detail and interest at the EP, and is easy to use.

I have thought about adding a filter (lots of good info here on CN about choices), but am reluctant to spend money on an experiment of this nature.

Ed


Post Extras: Print Post   Remind Me!   Notify Moderator  
coopman
Post Laureate
*****

Reged: 04/23/06

Loc: South Louisiana
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Ed Holland]
      #6488049 - 04/25/14 02:43 PM

I have various types of scopes too. I'd rather be using a 4" or sim. sized refractor as soon as the tripod hits the ground than another type of scope that will have cool down issues that reduce my observing time. Back when I had my C8, my refractors got a lot of use when the C8 proved to be unusable.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Ed Holland]
      #6488071 - 04/25/14 02:50 PM

Quote:

However, if I want a quick setup, rapid thermal settling and pleasing views without concerns for collimation etc., the AR5 or 102 are in the front line. Yes there are purple fringes, possibly also some spherical aberration (both of which change with temperature). But to me, these are good scopes that get used. I find it hard to get annoyed, concerned or disappointed about an instrument that is still providing detail and interest at the EP, and is easy to use.






One of my favorite John Wooden quotes:

"Don't let what you can't do interfere with what you can do.."

Enjoy your equipment for what it is and don't try to make it into something it is not...

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
Vondragonnoggin
Post Laureate
*****

Reged: 02/21/10

Loc: Southern CA, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6488091 - 04/25/14 02:59 PM

Quote:

Quote:

Again - filtering is the purposeful elimination or reduction in certain spectrum to enhance detail. Whether by eliminating bad information from aberrations or by fine tuning a frequency to bring more information that is swamped usually by your needless information (such as narrowband to eliminate unwanted spectrum) it is the same effect on different scales.




Well...

I am well aware of the purpose of filters. This is what your wrote:

Quote:

I don't know why these conversations don't go hand in hand, but there is always someone asking about which filters to buy for astronomy use and usual answers consist of UHC, OIII, H-Beta, or the like and everyone gets happy about the thought of getting a little MORE detail out of nebula viewing.

Mention achromat and filtering it out like with Longpass, or semi-apo, or minus V and suddenly people are worried and discussing how much LESS detail is seen.

People are okey dokey with one application and always whining about the other and it makes little sense to me.




You asked the question "why the conversation about filtering achromats and filtering deep sky objects do not go hand in hand."

I spent a considerable amount of time answering your question and explaining why they do not go hand in hand. Both involve the use of filters but the purpose is quite different.

One enhances object itself by only passing the very narrow band that the object itself emits whereas the other attempts to make up for optical deficiencies by discarding otherwise desirable information. I thought the radio analogy was particularly appropriate, with one, you are picking out a faint signal from the broad spectrum, the other, you are attempting to make up for deficiencies in the equipment.. a bad amplifier or fuzzed speaker.

I will also add that your implication that one only sees "a little MORE detail out of nebula viewing" is misleading and incorrect. The reality is that narrow band nebula filters greatly increase the contrast of many nebulae and in many cases allow them to be seen in detail when they would otherwise be invisible. Deep sky filters make huge differences for those objects which they enhance.

On the other hand, it is questionable whether the long pass, Semi-APO and minus violet filters actually enhance the detail seen. In my experience, the difference is primarily aesthetic and does not result in me seeing more details. As Mark does, I look past the purple haze, it is the remaining lack of sharp focus that seems to most affect the what I see.

If one wants to view the planets with an achromat, longer focal lengths, slower focal ratios are better. My goal here is to help folks just starting out understand their choices and what differences those choices make at the eyepiece and in the field. I do not generally recommend someone first starting out invest in an expensive apochromat. But at the same, since the original question was asked, sharing my experiences and understandings of the differences, there is a place for that.

I find the side by side comparison between my 4 inch F/5.4 apochromat and my 100mm F/6 Achromat quite enlightening. As much as I enjoy the achromat, as much as I love the thing, as much as I try different filters, different aperture masks and such, the difference between the two when viewing the planets is still very noticeable, nothing I have found does much in the way of closing the gap. Masking the 100mm achromat to an 80mm F/7.5 and then comparing it to my 80mm F/7 apochromat bears similar results..

Jon Isaacs




Thank you Jon, but I have Lumicon UHC, Lumicon OIII, Lumicon H-Beta, Baader 7nm H-Alpha, Baader 35nm H-Alpha, Baader 610nm Longpass, Thousand Oaks LP2, Baader Moon and Skyglow, Baader semi-apo, Baader 685nm IR Pass, and just ordered a Lumicon 640nm longpass. All of which get used actively with primarily 7nm, 610nm use.

the purpose remains the same - to bring out more detail. You can try to word it how you like, but no different in my eyes. Useful info like Mercury and Sodium lines? useful like IR data for pure visual use?

Nice try to school me about filter basics, but really you're talking to the wrong person trying to school me on it.

I'm out of the beginner section for this reason - getting snippets pulled and quoted that neglect 80% of what I'm saying only to have it worded slightly different. Have fun with it.



Post Extras: Print Post   Remind Me!   Notify Moderator  
rsimpkins
super member


Reged: 04/11/14

Loc: Lehi, UT
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6488155 - 04/25/14 03:20 PM

What a lot of great information. I am quickly becoming enamored with the idea of owning an APO refractor, largely based on the information in this thread.

Despite my desire to wait until I gain more experience before buying, I am now kicking myself for not just ponying up for the ES 127CF when it was on sale from Astronomics a couple weekends ago. I simply didn't have enough knowledge at the time to know that was a good deal. Something like that might not come along again for a very long time. Makes a person feel kind of rotten inside.

Now the long wait begins looking for the next great opportunity. I will be sure not to miss it. How often do telescopes in this price range go on sale?


Post Extras: Print Post   Remind Me!   Notify Moderator  
GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6488208 - 04/25/14 03:39 PM

Lots of sales come up during the year. You may want to consider the carbon fiber a bit more. Not sure how the affect refractors but I understand they have some unique characteristics in use. I think just a normal tube may be better from what I have seen on here.

I see that Optcorp.com has that scope discounted. I'm more into doublets than triplets. Quicker cool down and lighter weight, but maybe do not have perfect color correction...but pretty darn close in my experience.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6488258 - 04/25/14 03:59 PM

Quote:

What a lot of great information. I am quickly becoming enamored with the idea of owning an APO refractor, largely based on the information in this thread.




APOs are wonderful, no doubt about it. But just remember that Newtonians are even more free from color, at a tiny fraction of the cost. There's a reason that Newtonians have been the tool of choice for most serious planetary observers for more than a century.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Vondragonnoggin]
      #6488284 - 04/25/14 04:14 PM

Quote:

Nice try to school me about filter basics, but really you're talking to the wrong person trying to school me on it.





Eric:

Please be clear, I am not trying to school you on anything. I am trying help first time observers understand achromats, apochromats, the differences, and now, deep sky filters.


Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
Kevdog
Pooh-Bah
*****

Reged: 07/11/12

Loc: Desert Hills, AZ
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6488288 - 04/25/14 04:16 PM

Think of a prism. It spreads out the white light from the sun (or other source) into a rainbow of colors. A lens is basically a prism that varies across it's diameter.
The more precisely it is built, the narrower the band of the prism effect. (+ $$$)
The better the glass is, the more narrow the band of the prism effect. (+ $$$)
Using more lenses can narrow the band of the prism effect. (+$$$)
Better coatings can narrow the band of the prism effect (+$$$)
A longer focal length narrows the band of the prism (+ length/weight)

The more precisely each band of light is bent to be the same as the others, the clearer your image is. Camera lenses are the same. There's a reason that a $200 "kit" lens doesn't have near as sharp a picture as a $2000 lens. Better glass, better engineering, better coatings.

It's not just the purple color that's getting moved about, it's the other bands as well. That's why you lose detail and sharpness. It's just the purple gets "thrown off the edge" while the others "mix in the middle", which hurts sharpness and contrast between the color boundaries.

So a cheap achro can show lots of purple (and lots of loss in sharpness and contrast) due to average mfg tolerances, cheaper glass and coatings.
An expensive achro will greatly reduce it (better engineering, glass and coatings)
A "cheap" APO may be similar to an expensive achro if the engineering and the coatings don't make up for the extra glass (I'm not sure if these exist, but I'm betting there's at least a couple out there)
An expensive APO combines all the best stuff together to make that light converge as closely as possible.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Tony Flanders]
      #6488291 - 04/25/14 04:18 PM

Quote:

Quote:

What a lot of great information. I am quickly becoming enamored with the idea of owning an APO refractor, largely based on the information in this thread.




APOs are wonderful, no doubt about it. But just remember that Newtonians are even more free from color, at a tiny fraction of the cost. There's a reason that Newtonians have been the tool of choice for most serious planetary observers for more than a century.






A 4 inch apo can provide the best possible views that a 4 inch telescope can provide...

But a decent 10 inch Newtonian will, if cooled and collimated, and if the seeing is decent, provide more planetary detail, more fine scale contrast. It's more effort but it pays off at the eyepiece.

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6488313 - 04/25/14 04:34 PM

We should point out the other benefit of the 10 inch dob. DSOs such as Globular Clusters come out and say hello! To me that was the biggest difference between a smaller scope and the 10 inch. And even more fun in a dark sky.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Abhat
sage
*****

Reged: 12/14/13

Loc: Middletown, MD
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6488321 - 04/25/14 04:39 PM

If we compare apples to apples, would 4" or 5" Newtonian cool just as fast AND be just as portable as a 4" APO refractor and provide similar CA free views?

If it is pretty close then what are other technical reasons I would want to buy 4" APO and not a 4"/5" Newtonian at 1/10th the price.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Ed Holland
Carpal Tunnel


Reged: 06/16/10

Loc: San Jose, CA and Oxford, UK
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Abhat]
      #6488329 - 04/25/14 04:46 PM

I also have a "beginner level" 4.5" f/8 Newtonian reflector. It gives excellent views, colour free of course . That telescope afforded me the first ever look at a Jovian shadow transit. Again, very useable instrument - especially as it was the only 'scope I had at the time.

It is easy to be spoiled


Post Extras: Print Post   Remind Me!   Notify Moderator  
GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Abhat]
      #6488335 - 04/25/14 04:51 PM

Personally I don't think a 4-5 inch newt would cool as fast. especially if it were really cold out. My 4 inch refractor takes about 15-20 minutes when it is 20 degrees F. That's pretty darn fast. Mine is a doublet though...I'd imagine a triplet may take another little bit.

My guess is a 4-5 inch newt would be more like 45 minutes to an hour in that situation.

I think quality needs to be brought up here as well. Most apo refractors are of better quality all around (focusers, etc). So it's more than just the expensive glass. But, certainly you can get a decent newt for cheap. The XT6 I had only cost me $235 new (they are more like $300 now). It rivaled my 4 inch apo...not as sharp and not as good mechanics, but brighter and still very capable.

I think some of the smaller newts do not appear to have the same quality as the larger ones. Kind of depends on the company. Of course you can get a 5 inch Takahashi newt for $3000...so even with a newt you can pay for quality. Of course it is somewhat of a specialized newt for imaging.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Dave Lee
sage


Reged: 02/14/13

Loc: Pinehurst, NC USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6488339 - 04/25/14 04:56 PM

Quote:

Quote:

Nice try to school me about filter basics, but really you're talking to the wrong person trying to school me on it.





Eric:

Please be clear, I am not trying to school you on anything. I am trying help first time observers understand achromats, apochromats, the differences, and now, deep sky filters.


Jon




Jon, thank you for stating this clearly, concisely, and better than I was about to.

dave


Post Extras: Print Post   Remind Me!   Notify Moderator  
StarStuff1
Post Laureate
*****

Reged: 04/01/07

Loc: South of the Mason-Dixon Line
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Dave Lee]
      #6488384 - 04/25/14 05:21 PM

Dave, golfing will cost you as much or more than astronomy. Be careful out there!

ps: better apo than achro if same aperture and focal ratio


Post Extras: Print Post   Remind Me!   Notify Moderator  
Dave Lee
sage


Reged: 02/14/13

Loc: Pinehurst, NC USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: StarStuff1]
      #6488424 - 04/25/14 05:42 PM

Quote:

Dave, golfing will cost you as much or more than astronomy. Be careful out there!

ps: better apo than achro if same aperture and focal ratio




This is interesting. In golf the expense is primarily in the "process of playing the game". While you can spend as much as you wish on high end golf equipment , ultimately the costs pale in comparison to high end astro equipment costs. But the process of 'observing' from the best of locations, while maybe involving some travel expense, tends to be low cost or free compared to "the equivalent" golf experience (as in a really high end course like Pebble Beach).

That aspect of the two hobbies is most interesting, IMHO.

dave


Post Extras: Print Post   Remind Me!   Notify Moderator  
*skyguy*
Carpal Tunnel
*****

Reged: 12/31/08

Loc: Western New York
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: StarStuff1]
      #6488471 - 04/25/14 05:58 PM

Achromatic come from the Greek word "akhromatos" ... meaning "without color".

Apochromatic also means "without color ... except this time we really mean it ... well, at least some of the time!"


Post Extras: Print Post   Remind Me!   Notify Moderator  
obin robinson
Carpal Tunnel
*****

Reged: 10/25/12

Loc: League City, TX
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Abhat]
      #6488490 - 04/25/14 06:06 PM

Quote:

If it is pretty close then what are other technical reasons I would want to buy 4" APO and not a 4"/5" Newtonian at 1/10th the price.




The 4" apo makes a heck of a camera lens or spotting scope. It also is going to be a bit easier to travel with especially if you fly a lot. With an apo you have a quick setup and you don't have to mess with collimation. They also will retain their value over a long time. Just look at how the Pentax, Tele Vue and Takahashi apos hold up over time compared to a newt that was 1/10 of the price.

I'd get this in a heartbeat if I wasn't aggressively paying off some loans. http://www.vixenoptics.com/refractors/VSD.html

obin


Post Extras: Print Post   Remind Me!   Notify Moderator  
LDW47
scholastic sledgehammer


Reged: 03/04/12

Loc: North Bay,Ontario,Canada
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Kevdog]
      #6488701 - 04/25/14 08:15 PM

Quote:

Think of a prism. It spreads out the white light from the sun (or other source) into a rainbow of colors. A lens is basically a prism that varies across it's diameter.
The more precisely it is built, the narrower the band of the prism effect. (+ $$$)
The better the glass is, the more narrow the band of the prism effect. (+ $$$)
Using more lenses can narrow the band of the prism effect. (+$$$)
Better coatings can narrow the band of the prism effect (+$$$)
A longer focal length narrows the band of the prism (+ length/weight)

The more precisely each band of light is bent to be the same as the others, the clearer your image is. Camera lenses are the same. There's a reason that a $200 "kit" lens doesn't have near as sharp a picture as a $2000 lens. Better glass, better engineering, better coatings.

It's not just the purple color that's getting moved about, it's the other bands as well. That's why you lose detail and sharpness. It's just the purple gets "thrown off the edge" while the others "mix in the middle", which hurts sharpness and contrast between the color boundaries.

So a cheap achro can show lots of purple (and lots of loss in sharpness and contrast) due to average mfg tolerances, cheaper glass and coatings.
An expensive achro will greatly reduce it (better engineering, glass and coatings)
A "cheap" APO may be similar to an expensive achro if the engineering and the coatings don't make up for the extra glass (I'm not sure if these exist, but I'm betting there's at least a couple out there)
An expensive APO combines all the best stuff together to make that light converge as closely as possible.


Then throw in just average seeing that you get at least 50% of the time or more on those clear nights and what do you get for all your $$$$ ? Is it really worth it ? Maybe we should work that into the mix when educating newcomers ? It always seems to get lost in the expertise thrown about between experts as they "educate" those less expert !

Post Extras: Print Post   Remind Me!   Notify Moderator  
David PavlichAdministrator
Transmographied
*****

Reged: 05/18/05

Loc: Mandeville, LA USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: jgraham]
      #6488888 - 04/25/14 10:15 PM

Quote:

"...but at f8, it's not as bad as the faster AR6 class..."

Hmmm, the AR6 is also f/8. The ES6s are f/6.5s. I took a hard look at the ES152 before settling on a used AR6. I was concerned about the color in a faster achromat. It turned out okay for me.




My error!

David


Post Extras: Print Post   Remind Me!   Notify Moderator  
jgraham
Postmaster
*****

Reged: 12/02/04

Loc: Miami Valley Astronomical Soci...
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: David Pavlich]
      #6488929 - 04/25/14 10:41 PM



Post Extras: Print Post   Remind Me!   Notify Moderator  
keithlt
super member
*****

Reged: 12/21/13

Loc: Arizona
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: jgraham]
      #6488937 - 04/25/14 10:51 PM

great info in this thread, so if a person is color blind an AR would better?

Post Extras: Print Post   Remind Me!   Notify Moderator  
Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Abhat]
      #6489228 - 04/26/14 05:55 AM

Quote:

If we compare apples to apples, would 4" or 5" Newtonian cool just as fast AND be just as portable as a 4" APO refractor and provide similar CA free views?




As far as CA is concerned, Newtonians are always better than APOs. False color is inherent in refractors -- it may be too small for you to see, but it's always there. Conversely, Newtonians are inherently 100% color-free.

However, CA is not the end of the story. Newtonians have central obstructions, which degrade the image significantly, though in a completely different way from chromatic aberration. And unless they have first-class mirrors, they also scatter more light than refractors.

Putting it all together, I would say that a first-rate 5-inch f/5 Newtonian would deliver about the same planetary detail as a first-rate 4-inch f/6 APO. And with the aid of a fan, it would cool nearly as fast -- but probably still not as fast. In terms of portability, it would be roughly a draw. The Newtonian tube would be a smidge bigger, but it would require a shorter mount because you view from the top rather than the bottom of the tube.

However, a first-rate 5-inch f/5 Newtonian with a fan is not a standard commodity! You could get one custom-made for less than the cost of most 4-inch APOs, but it still wouldn't be cheap.

A more normal comparison is between a 4-inch f/6 APO and a standard commercial 6-inch f/8 Dob. Here, the Dob will cost much less and deliver significantly better planetary images. But it will take longer to cool and be significantly less portable.


Post Extras: Print Post   Remind Me!   Notify Moderator  
LDW47
scholastic sledgehammer


Reged: 03/04/12

Loc: North Bay,Ontario,Canada
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Tony Flanders]
      #6489289 - 04/26/14 07:39 AM

Quote:

Quote:

If we compare apples to apples, would 4" or 5" Newtonian cool just as fast AND be just as portable as a 4" APO refractor and provide similar CA free views?




As far as CA is concerned, Newtonians are always better than APOs. False color is inherent in refractors -- it may be too small for you to see, but it's always there. Conversely, Newtonians are inherently 100% color-free.

However, CA is not the end of the story. Newtonians have central obstructions, which degrade the image significantly, though in a completely different way from chromatic aberration. And unless they have first-class mirrors, they also scatter more light than refractors.

Putting it all together, I would say that a first-rate 5-inch f/5 Newtonian would deliver about the same planetary detail as a first-rate 4-inch f/6 APO. And with the aid of a fan, it would cool nearly as fast -- but probably still not as fast. In terms of portability, it would be roughly a draw. The Newtonian tube would be a smidge bigger, but it would require a shorter mount because you view from the top rather than the bottom of the tube.

However, a first-rate 5-inch f/5 Newtonian with a fan is not a standard commodity! You could get one custom-made for less than the cost of most 4-inch APOs, but it still wouldn't be cheap.

A more normal comparison is between a 4-inch f/6 APO and a standard commercial 6-inch f/8 Dob. Here, the Dob will cost much less and deliver significantly better planetary images. But it will take longer to cool and be significantly less portable.


If you leave it in an unheated / vented shed / garage at the same or close to the same temp as the outside cooldown is negligible if at all. The key is venting / air circulation in your storage area especially in the more humid climates. Also a 6" Dob is still very portable for 90% of observers.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: keithlt]
      #6489309 - 04/26/14 08:08 AM

Quote:

great info in this thread, so if a person is color blind an AR would better?




No, not at all! The fundamental problem with achromatic refractors isn't the appearance of color, but the fact that only (at most) two wavelengths can be in focus at one time. The malfocused red and violet light will smear the image regardless of whether you can perceive the colors themselves.


Post Extras: Print Post   Remind Me!   Notify Moderator  
schang
scholastic sledgehammer


Reged: 04/24/13

Loc: columbia, sc
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Tony Flanders]
      #6489317 - 04/26/14 08:13 AM

Quote:


As far as CA is concerned, Newtonians are always better than APOs. False color is inherent in refractors -- it may be too small for you to see, but it's always there. Conversely, Newtonians are inherently 100% color-free.



I think this should be put it in a bulletin or somewhere newbies can easily see. It is delusional for them to read those glorified reviews about APOs without thinking that it is still a refractor. Same for Newtonian, where it is CA free, but it has some quirks as well that can be posted in the same space for newbies to see all at once, rather than going thru the maze of big cannons and small "rifles".


Post Extras: Print Post   Remind Me!   Notify Moderator  
schang
scholastic sledgehammer


Reged: 04/24/13

Loc: columbia, sc
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: LDW47]
      #6489333 - 04/26/14 08:22 AM

Quote:

If you leave it in an unheated / vented shed / garage at the same or close to the same temp as the outside cooldown is negligible if at all. The key is venting / air circulation in your storage area especially in the more humid climates. Also a 6" Dob is still very portable for 90% of observers.


This is one point neglected by a lot of people. Due to the size and low cost of newtonians/dobs, most would put them in the shed or garage where the mirror temp is quite close to the ambient temp. I do not know if this is the case for expensive APOs. I'd think that people would store them in the closet or display them in the great room.

Post Extras: Print Post   Remind Me!   Notify Moderator  
howard929
Member
*****

Reged: 01/02/11

Loc: Low End of High Ground
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: schang]
      #6489344 - 04/26/14 08:29 AM

Half of the time, 100 percent of first time buyers feel their requirements for said telescope are singular. Add to that a general feeling that as things change over time, there just may be something new and different to find out about. Long threads, short threads.. it's all good.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Abhat]
      #6489607 - 04/26/14 10:59 AM

Quote:

If we compare apples to apples, would 4" or 5" Newtonian cool just as fast AND be just as portable as a 4" APO refractor and provide similar CA free views?

If it is pretty close then what are other technical reasons I would want to buy 4" APO and not a 4"/5" Newtonian at 1/10th the price.




This is my experience, Three scopes to compare:

4 inch F/5.4 apo TeleVue refractor, Orion 100mm F/6 achromat fitted with a 2 speed focuser, Skywatcher 130mm F/5 Newtonian. The Skywatcher is fitted with a JMI DX-1 2 speed focuser.

Thermally: The two refractors need very little cool down and provide very nice views the moment they are taken out the door. The Newtonian is a totally different beast. The effect of the cooling mirror is very evident and it takes 45 minutes or more for it to settle down so it performs reasonably well at higher magnifications.

There are a number of reasons that can explain this, most of them involve tube currents, convection currents rising from the cooling mirror that disturb the air in the scope.

- With a refractor, the glass which cools the slowest is at the open end of the tube so the convection currents are not trapped, they only have to escape the dew shield. Also, the light only passes down the tube once and for more of that distance it's well separated from edge of the tube where tube currents are most likely. With the Newtonian, that first pass most of the light is along the edge and there is a second pass to the diagonal.

- Optically, the central obstruction of a Newtonian is always a compromise between high power work and low power widefield observing. A small secondary mirror provides greater planetary contrast and is better for high powers but means the low power views will not be well illuminated at the edge of the field. A large secondary results in better low power views but loss of contrast for planetary viewing. The smaller the scope, the more important this is because the field stop size of the eyepieces available are limited.

With a 5 inch Newtonian the compromise is serious, a 30% CO is about right. With a 25 inch Newtonian, one has a lot of latitude. Mine has a 14% secondary (3.5 inches) and provides a well illuminated widefield view.

Back to the comparison.. Viewing Jupiter and Saturn, the 4 inch apo provides the most contrast and shows the most detail. For most double stars, particularly unequal double stars, the apo is the better tool. Once it is cooled down, the Skywatcher 130mm F/5 does a nice job viewing the planets and many doubles, the contrast is there and the view is clean and free from chromatic aberration. At the high magnifications, the 100mm F/6 achromat suffers, the chromatic aberration significantly affecting the planetary views and limiting it's capabilities splitting close doubles.

At low magnifications, those big, bright wide fields of view that smaller scopes can do that big scopes cannot.. The 4 inch TeleVue apo refractor is about as perfect a telescope as there is. Not only does it have that amazing color correction but it has a flat field of view so stars are in focus from the center to the edge. The 100mm achromat does a good job, it shows field curvature so the stars are not pinpoint across the field but it's a pretty fine view.

The 130mm Newtonian does a reasonable job as well but suffers from a drop in illumination at low powers. Still, I can see the entire Veil in one view...

Bottom line:

A scope like the NP-101 is very expensive, it's value is in the quality of the view. For a 4 inch telescope that is 26 inches long, it does just about everything a 4 inch telescope can do as well as it can be done.. If one is interested in high magnifications, it is limited by it's 4 inch aperture and there are many more affordable alternatives that are of a larger aperture that provide more detailed views, views with finer contrast of the planets and double stars.

At the lowest magnifications, it is arguably the best visual scope there is but others do a satisfactory job without the hefty price tag.

At telescope like this.. it's easy to use because it is compact, it provides wonderful views that approach perfection, when you look through the eyepiece, you know you are looking through something very special...

But all that said, when I want the best planetary views and I have time to setup and time for a Newtonian to cool down, my basic 10 inch GSO Dob provides the better planetary views.

As I said, I don't recommend expensive apo refractors to most beginning astronomers. But there comes a time when it is nice to have one.

Jon





Post Extras: Print Post   Remind Me!   Notify Moderator  
GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: schang]
      #6489650 - 04/26/14 11:21 AM

Quote:

This is one point neglected by a lot of people. Due to the size and low cost of newtonians/dobs, most would put them in the shed or garage where the mirror temp is quite close to the ambient temp. I do not know if this is the case for expensive APOs. I'd think that people would store them in the closet or display them in the great room.




Personally I wouldn't store any of my scopes in the garage. To many contaminates from cars and such. Unless it were a garage that did not have cars or other pollutants in it. Sheds could work as long as they are secure and well maintained temperature wise. I don't have a means of storing mine other than in the house. Sometimes I will bring mine into the garage for a short time if the outside temp is really cold in order to phase the warm up.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Abhat
sage
*****

Reged: 12/14/13

Loc: Middletown, MD
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6489669 - 04/26/14 11:28 AM

Thanks Jon. As always, I truly appreciate the time you take to write this for us. And also your detailed and easy to understand explanations are very informative.

By the way those pictures look great. Few years down the line I hope I would have gathered enough courage and experience to buy that TV APO.

Edited by Abhat (04/26/14 11:35 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: GOLGO13]
      #6489686 - 04/26/14 11:36 AM

Quote:

Personally I wouldn't store any of my scopes in the garage. To many contaminates from cars and such. Unless it were a garage that did not have cars or other pollutants in it.




Cars in the garage?

In San Diego, cars mostly live outdoors all year long. No one has a basement, no one has an real attic, garages are for telescopes, bicycles and the like..

For those who live in the real world with real weather, I would also be reluctant to keep my scope in a garage with cars the like.

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
obin robinson
Carpal Tunnel
*****

Reged: 10/25/12

Loc: League City, TX
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: GOLGO13]
      #6489771 - 04/26/14 12:29 PM

Quote:

Personally I wouldn't store any of my scopes in the garage. To many contaminates from cars and such. Unless it were a garage that did not have cars or other pollutants in it. Sheds could work as long as they are secure and well maintained temperature wise. I don't have a means of storing mine other than in the house. Sometimes I will bring mine into the garage for a short time if the outside temp is really cold in order to phase the warm up.




Personally i wouldn't store anything outside that i don't want spiders eventually taking up a residence in. If you don't mind the occasional insect crawling out of your focuser then go ahead and store your telescope in a garage. Garages also have temperature extremes that can ruin certain materials. Due to those temperature and humidity extremes corrosion of small parts will be accelerated in a garage. You also risk warpage of materials from heat. On top of that dirt and film from car exhaust gathers on everything which is stored in a garage.

obin


Post Extras: Print Post   Remind Me!   Notify Moderator  
schang
scholastic sledgehammer


Reged: 04/24/13

Loc: columbia, sc
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: GOLGO13]
      #6489925 - 04/26/14 01:47 PM

Quote:

Quote:

This is one point neglected by a lot of people. Due to the size and low cost of newtonians/dobs, most would put them in the shed or garage where the mirror temp is quite close to the ambient temp. I do not know if this is the case for expensive APOs. I'd think that people would store them in the closet or display them in the great room.




Personally I wouldn't store any of my scopes in the garage. To many contaminates from cars and such. Unless it were a garage that did not have cars or other pollutants in it. Sheds could work as long as they are secure and well maintained temperature wise. I don't have a means of storing mine other than in the house. Sometimes I will bring mine into the garage for a short time if the outside temp is really cold in order to phase the warm up.



There are contaminants all around the house, no better than the garage. If you cover your scope with a large plastic bag (I mean large one to cover from top to bottom), in addition to the lid, you will be fine. If you like the hassle of moving it in and out of the house, that is OK, you are not going to hurt my feeling...


Post Extras: Print Post   Remind Me!   Notify Moderator  
Widespread
professor emeritus


Reged: 05/11/11

Loc: Bowling Green, Kentucky
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6489992 - 04/26/14 02:21 PM

Quote:

Quote:

Personally I wouldn't store any of my scopes in the garage. To many contaminates from cars and such. Unless it were a garage that did not have cars or other pollutants in it.




Cars in the garage?

In San Diego, cars mostly live outdoors all year long. No one has a basement, no one has an real attic, garages are for telescopes, bicycles and the like..

For those who live in the real world with real weather, I would also be reluctant to keep my scope in a garage with cars the like.

Jon




In the Bluegrass State, many keep riding mowers in the garage. Smells like gas, grass or... Oops... grease? (No one rides free)

But I suppose you could just leave the mower outside to outgas, or whatever, for a while before putting it away?


Post Extras: Print Post   Remind Me!   Notify Moderator  
GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: schang]
      #6490043 - 04/26/14 02:42 PM

I certainly cannot store my scopes in the garage in the summer. It gets super hot in there. But in the winter it may be better. However, salt and dirt is in the air as I store two cars in the garage.

Bottom line is it depends on your garage situation. As Jon points out (and I am extremely jealous) he doesn't have issues. Then again, the cost of living is about 1/6th the cost where I live ... though for this hobby it may be worth it.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: GOLGO13]
      #6490120 - 04/26/14 03:18 PM

I think the bottom line is there are a lot of different garages, some are good for storing telescopes, some not so good. Some folks store their scopes outside in a shed or even just under a cover. I wouldn't do that, too much dust. But I do store them in an unheated garage. It never gets too hot because there is just always a "breeze" blowing and it gets cool at night, this is in the mountains so there can be snow, but never too cold to store a scope.

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
LDW47
scholastic sledgehammer


Reged: 03/04/12

Loc: North Bay,Ontario,Canada
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6490417 - 04/26/14 05:55 PM

Quote:

I think the bottom line is there are a lot of different garages, some are good for storing telescopes, some not so good. Some folks store their scopes outside in a shed or even just under a cover. I wouldn't do that, too much dust. But I do store them in an unheated garage. It never gets too hot because there is just always a "breeze" blowing and it gets cool at night, this is in the mountains so there can be snow, but never too cold to store a scope.

Jon


As I mentioned it all depends where you live and your average climate compensated by good venting / air circulation in your storage area. I am fortunate to live in a pretty temperate climate with no prolonged extremes and it all comes together perfectly.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Widespread
professor emeritus


Reged: 05/11/11

Loc: Bowling Green, Kentucky
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: LDW47]
      #6490424 - 04/26/14 05:59 PM

Yep!

Post Extras: Print Post   Remind Me!   Notify Moderator  
Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: LDW47]
      #6491272 - 04/27/14 04:55 AM

Quote:

Quote:

I think the bottom line is there are a lot of different garages, some are good for storing telescopes, some not so good ...




As I mentioned it all depends where you live and your average climate ...




Actually, I think it depends a lot more on what else you keep in your garage. Obviously, I don't have a garage for my city apartment, but I do at my country home.

Keep a car in the garage? Why ever would I do that? That's not what garages are for, is it?


Post Extras: Print Post   Remind Me!   Notify Moderator  
LDW47
scholastic sledgehammer


Reged: 03/04/12

Loc: North Bay,Ontario,Canada
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Tony Flanders]
      #6491365 - 04/27/14 07:52 AM

Quote:

Quote:

Quote:

I think the bottom line is there are a lot of different garages, some are good for storing telescopes, some not so good ...




As I mentioned it all depends where you live and your average climate ...




Actually, I think it depends a lot more on what else you keep in your garage. Obviously, I don't have a garage for my city apartment, but I do at my country home.

Keep a car in the garage? Why ever would I do that? That's not what garages are for, is it?


If you are unlucky enough to not have a telescope then probably ! LOL !

Post Extras: Print Post   Remind Me!   Notify Moderator  
REC
Post Laureate
*****

Reged: 10/20/10

Loc: NC
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: LDW47]
      #6491413 - 04/27/14 08:36 AM

Just an FYI...I had my C102 out last night for a short time. High clouds in and out. I used my 8-24 zoom EP and had very little CA. When I zoomed all the way in to 8mm at 125x the CA was a little more produced. I had 2 bands, but backing it off a little to like 12mm @80x, I had 3 bands and very little CA. Overall, it was not bothersome and the 4 moon where very sharp. BTW...this is with a $69 zoom EP.

Post Extras: Print Post   Remind Me!   Notify Moderator  
schang
scholastic sledgehammer


Reged: 04/24/13

Loc: columbia, sc
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: REC]
      #6491551 - 04/27/14 10:34 AM

Quote:

Just an FYI...I had my C102 out last night for a short time. High clouds in and out. I used my 8-24 zoom EP and had very little CA. When I zoomed all the way in to 8mm at 125x the CA was a little more produced. I had 2 bands, but backing it off a little to like 12mm @80x, I had 3 bands and very little CA. Overall, it was not bothersome and the 4 moon where very sharp. BTW...this is with a $69 zoom EP.



I used my C102AZ as well last night to try the modified AZ tripod. CA on the C102 is there at 167X on Mars, Jupiter, and Saturn, but not much. I saw color fringing on my Dob as well on Jupiter when it is setting low around 11:30 PM. Mars was high and I pushed it to 212X and still not much CA. Overall, I am not too concerned about CA with a slower refractor. In observing, bad seeing, low hanging objects and poor alignment would have much severe impacts on images than CA from a slower achromatic refractor.


Post Extras: Print Post   Remind Me!   Notify Moderator  
finisher604
member


Reged: 02/17/14

Loc: Vancouver , Canada
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: schang]
      #6491737 - 04/27/14 12:33 PM

I made the jump to an expensive apo. I use it every clear night. I too am spoiled like Jon and keep my gear in the garage. The scope it's self is in a case which would solve everyone else issues with bugs and dust. My eye pieces are all in a plastic case to keep the dust out. In the winter is heat the garage with a space heater just to keep the dampness out of the air. No problems yet and my motorcycle is showing no signs of rust either

Post Extras: Print Post   Remind Me!   Notify Moderator  
obin robinson
Carpal Tunnel
*****

Reged: 10/25/12

Loc: League City, TX
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: finisher604]
      #6491783 - 04/27/14 01:05 PM

Quote:

In the winter is heat the garage with a space heater just to keep the dampness out of the air. No problems yet and my motorcycle is showing no signs of rust either




That's the key right there. As long as you keep the moisture levels to a minimum you will be fine. On the other hand when we lived in New York I can remember people being surprised at how much their cars were rusting even when in a garage. Moisture + salt + dirt + temperature changes = corrosion. Keep something dry and clean and the corrosion process will be slowed.

obin


Post Extras: Print Post   Remind Me!   Notify Moderator  
Abhat
sage
*****

Reged: 12/14/13

Loc: Middletown, MD
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: schang]
      #6491798 - 04/27/14 01:13 PM

Quote:

Overall, I am not too concerned about CA with a slower refractor. In observing, bad seeing, low hanging objects and poor alignment would have much severe impacts on images than CA from a slower achromatic refractor.




Thats a good point. Seeing, collimation, cooling, dew, poor mount, light pollution etc.. There are so many factors that kick in before one starts wishing about the premium optics. In my limited personal experience optics is never the weakest link in the chain. That's why I hate to throw money at $300 eyepieces when you can buy a decent slow refractor with the same money.


Post Extras: Print Post   Remind Me!   Notify Moderator  
SpooPoker
sage
*****

Reged: 06/04/13

Loc: North Bay CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Abhat]
      #6491990 - 04/27/14 02:47 PM

I am not too sure on the details, but maybe someone can expand upon this. In terms of contrast with an achromat, I believe if the scope is Sidgwick level, the contrast factor is a two instead of one (i.e. unity being the perfect refractor). It works out, in notions of equivalence, that if an achromat had a CA index = 3, it would have a similar effect on contrast as a Newtonian of same aperture obstructed by 25%.

I do not remember where I read this, or what it means, but more knowledgeable here could expand on this point and correct my "misinformation".

I have noticed this though:

4" f/9 ED/APO Vs 4" f/11 ACHRO Vs 4" f/10 NEWT:

The 4" APO provides the best and most aesthetically crisp planetary images, the 4" ACHRO and NEWT are roughly tied in terms of planetary contrast. In none of the these scopes did I see more detail than the other on, say, Jupiter. It was pretty much a 3 way tie on this front. However, 4" of aperture is pretty meagre, the comparison on a 6" f/8'ish rigs between the 3 would be more interesting.

An achromat = beautiful classics, but outgunned by the APO. Most would not purchase them if the APO was equivalently priced. They can be fine telescopes though.


Post Extras: Print Post   Remind Me!   Notify Moderator  
schang
scholastic sledgehammer


Reged: 04/24/13

Loc: columbia, sc
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: SpooPoker]
      #6492154 - 04/27/14 04:13 PM

Quote:

An achromat = beautiful classics, but outgunned by the APO. Most would not purchase them if the APO was equivalently priced. They can be fine telescopes though.



That is a big "if". I bet if there are quadruplets or quintuplets APO priced like a achromatic refractor, people want to purchase them too. For each additional color correction, the cost increase substantially with diminished return on performance. People buy stuffs based on their perceived cost/performance consideration, which varies significantly among people in the world. The key is to enjoy what you have, not to fuzz about what you do not have (or want).


Post Extras: Print Post   Remind Me!   Notify Moderator  
Andy Taylor
Twisted, but in a Good Way
*****

Reged: 09/24/08

Loc: Epsom - UK
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: schang]
      #6492281 - 04/27/14 05:34 PM

I use two scopes. One is a 100mm F13 vintage achro Carton objecive and the other is a modern (Skywatcher) 8" F5 newt.

For visual use the Carton blows my socks off. The contrast & detail is awesome! The newt has diffraction spikes that irritates me no end.

So...

The Carton I use for visual and the newt I use for imaging planets.

Strange - on axis views with the Carton the violet halo seems to disappear. This objective is renowned for it's quality. Maybe due to eyepiece combination - I dunno.

All I can say is that you will have to wrench it from my dead hands...


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: SpooPoker]
      #6492443 - 04/27/14 06:51 PM

Quote:

I am not too sure on the details, but maybe someone can expand upon this. In terms of contrast with an achromat, I believe if the scope is Sidgwick level, the contrast factor is a two instead of one (i.e. unity being the perfect refractor). It works out, in notions of equivalence, that if an achromat had a CA index = 3, it would have a similar effect on contrast as a Newtonian of same aperture obstructed by 25%.




These are two different aberrations so it is difficult to compare them. However, Suiter, in Star Testing Astronomical Telescopes shows some simple analysis that suggests that the CR= 3 is approximately equal to 1/2 wave of spherical aberration in terms of loss of contrast. A Newtonian with a 25% CO has much less effect.

Jon Isaacs


Post Extras: Print Post   Remind Me!   Notify Moderator  
jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: EJN]
      #6492848 - 04/27/14 10:21 PM

Conrady for the win. An f/15 4-incher is still a colorful kaleidoscope, which wouldn't bode well for an f/15 5-incher on the color correction front.

- Jim


Post Extras: Print Post   Remind Me!   Notify Moderator  
jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6492863 - 04/27/14 10:30 PM

"A Newtonian with a 25% CO has much less effect."

At least from the CO. There are other features of the Newtonian that interfere with contrast - spider arms, imperfect baffling/blackening in some designs, etc. The CO is only one contrast robbing culprit, and probably the single biggest, but not the only.

Regards,

Jim


Post Extras: Print Post   Remind Me!   Notify Moderator  
SpooPoker
sage
*****

Reged: 06/04/13

Loc: North Bay CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: jrbarnett]
      #6493166 - 04/28/14 02:25 AM

Quote:


These are two different aberrations so it is difficult to compare them. However, Suiter, in Star Testing Astronomical Telescopes shows some simple analysis that suggests that the CR= 3 is approximately equal to 1/2 wave of spherical aberration in terms of loss of contrast. A Newtonian with a 25% CO has much less effect.
Jon Isaacs





Ouch, that is one heck of an error. What happens to the airy disc in a colorful achromat? In a Newtonian, it is pretty basic, all colors come together nicely, the mirror should, knock on wood, give a perfect image within diffraction laws. Once an obstruction is added in, energy is added into the rings due to additional source of diffraction. The amount of energy not going into the center dot is proportional to the size of the obstruction. The size of the disc itself is inversely proportional to the aperture.

On the achromat, what happens to the airy disc because of unfocused color? I presume the airy disc size is inversely proportional to aperture, but where does the unfocussed color go?


Quote:

I use two scopes. One is a 100mm F13 vintage achro Carton objecive and the other is a modern (Skywatcher) 8" F5 newt.

For visual use the Carton blows my socks off. The contrast & detail is awesome! The newt has diffraction spikes that irritates me no end.

All I can say is that you will have to wrench it from my dead hands...





That is a good quality achromat - I saw one of these at a get together and enjoyed peeking through it. A good 4" achromat / apo is great to own and use, and that one is a keeper.


Quote:

Conrady for the win. An f/15 4-incher is still a colorful kaleidoscope, which wouldn't bode well for an f/15 5-incher on the color correction front.
- Jim





I will say, even with the color being terrible for a 6" f/12, I definitely noticed more detail on Jupiter with it than a 4" f/15 Achro. Not saying I like the powerful violet/indigo halo that a 6" achromat chucks out, but I will give it some kudos for showing detail despite the psychedelic "purple haze". Should play that song next time I look through it - not sure Jimmy was singing about CA in telescopes though .


Quote:

"A Newtonian with a 25% CO has much less effect."

At least from the CO. There are other features of the Newtonian that interfere with contrast - spider arms, imperfect baffling/blackening in some designs, etc. The CO is only one contrast robbing culprit, and probably the single biggest, but not the only.

Regards,

Jim




You are right, there are a lot of contrast robbing fiends for the Newtonian design. Of them all, I am pretty sure that the CO is an area of lesser concern (as long as it is below 20% or so). I reckon mirror smoothness and figure are major players here. A good 7" MAK has a huge obstruction typically 25 - 30% and the one I looked through (a Questar) definitely showed planets as contrasty and crisp. It actually kicked the orthoscopic eyepiece off of my 8" f/6 DOB with its smaller obstruction at 19%. An EQ mounted 8" f/6 CAVE I have performs much better, even with a larger obstruction at 23%. I am sure the big difference is the optical quality.

Those folks that champion the so-called premium Newtonian find that their scopes work so well at the eyepiece because they do - they are optically sound and mechanically proficient. The low scatter, smooth, well figured and cooled mirror is to Newtonians what the Chromacor was to the achromat. It turns mush into beauty.

Cannot beat good quality optics really - it is a prerequisite for any scope design - whether a Newt or APO or MAK. If any scope is built right, it will show right.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Ed Holland
Carpal Tunnel


Reged: 06/16/10

Loc: San Jose, CA and Oxford, UK
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: SpooPoker]
      #6493734 - 04/28/14 12:07 PM

Telescope designs eh? what a bumpy playing field.

Size, cost, degree of optical perfection all vary by orders of magnitude, and that is just for the more common designs.

Value - well that is determined by each individual owner according to their needs and enjoyment.

I sometimes wonder how often comments made about 'scope design have led someone to focus on some negative aspect of their telescope (CA might well be a good example) and then become dissatisfied with it? Peer pressure if you will.

Whatever you own - I hope you enjoy viewing


Post Extras: Print Post   Remind Me!   Notify Moderator  
csrlice12
Postmaster
*****

Reged: 05/22/12

Loc: Denver, CO
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Ed Holland]
      #6493769 - 04/28/14 12:21 PM



Post Extras: Print Post   Remind Me!   Notify Moderator  
javven
super member


Reged: 03/16/08

Loc: TX Metro-Mess
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: csrlice12]
      #6494083 - 04/28/14 03:09 PM

Discussions about equipment blow my mind. Even "The sheer physics are mind-boggling" just doesn't quite say it.

If you're -experienced- then these discussions are great.
If you're -new- find some local star parties and spend a month or two going to them. You'll get to look through telescopes probably from a hundred to likely several thousand dollars and it may surprise you. I'll never forget my first Tak experience. I'm thinking 'What's with this little 100mm thing...' and later find out it only costs a few months of my pay to own.

Great thing about star parties - WHO CARES. Look for yourself, under the skies where you live and decide what it is that you like to look at and want to continue to study. Bump that against "I might do that down the line" and make your decision, remembering that in the end it's hard to beat aperture especially if you're talking several inches at the same price point.

clear skies


Post Extras: Print Post   Remind Me!   Notify Moderator  
SpooPoker
sage
*****

Reged: 06/04/13

Loc: North Bay CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: javven]
      #6495038 - 04/29/14 12:19 AM

The thing about equipment is it is not cheap and it is very much part of the forte with astronomy. For me it is a matter of right choices, learning the subject as best as possible, and using money wisely to purchase the right tool for the job. Whether the tool is a Newtonian, Refractor or whatever else is not important, it is knowing the limitations and thus usage potential that will define a purchase. I, for one, do not wish to own more than around 6 or so scopes, and I am sure many here fall in the same category. Part of equipment discussion is territorial, i.e. the refractor guys vs newtonian guys. Whatever the case, I care for the details on what makes them tick and do not have a huge preference one over the other.

The trouble with information is sorting the wheat from the chaff. Emotions get involved, bias, and so on, making it difficult to learn anything. Some folks say a 6" APO will better a 20" DOB or the hubble space telescope on planets due to those scopes having obstructions, others suggest obstructions matter less in the face of aperture and thus a decent 7" MAK or 8" Newt will do as good a job depending on how the focal ratio and secondaries are fiddled with. There are opinions on two edges of the extreme, a middling ground seems to be illusive.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: SpooPoker]
      #6495245 - 04/29/14 06:55 AM

Quote:

Part of equipment discussion is territorial, i.e. the refractor guys vs newtonian guys.




Truth be told, I find it hard to think of any serious observer in my acquaintance who doesn't own -- or at least hasn't owned in the past -- both a refractor and a Newtonian.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Dave Lee
sage


Reged: 02/14/13

Loc: Pinehurst, NC USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Tony Flanders]
      #6495312 - 04/29/14 08:32 AM

Quote:

Quote:

Part of equipment discussion is territorial, i.e. the refractor guys vs newtonian guys.




Truth be told, I find it hard to think of any serious observer in my acquaintance who doesn't own -- or at least hasn't owned in the past -- both a refractor and a Newtonian.




FWIW, I have a total of around 10 years of (visual only) experience and have owned one Mak, three SCT's, and one refractor. Never owned a Newtonian (Dob or otherwise).

No particular reason or bias here - just never happened.

dave


Post Extras: Print Post   Remind Me!   Notify Moderator  
Mark9473
Postmaster
*****

Reged: 07/21/05

Loc: 51°N 4°E
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Dave Lee]
      #6495356 - 04/29/14 09:10 AM

Guess you (and I) won't make it to Tony's circle of acquaintances.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Dave Lee]
      #6495417 - 04/29/14 09:47 AM

Quote:

Quote:

Truth be told, I find it hard to think of any serious observer in my acquaintance who doesn't own -- or at least hasn't owned in the past -- both a refractor and a Newtonian.




FWIW, I have a total of around 10 years of (visual only) experience and have owned one Mak, three SCT's, and one refractor. Never owned a Newtonian (Dob or otherwise).




Yes, it certainly happens. But Newtonians and achromatic refractors being the two oldest effective designs -- and also the simplest -- either one or both makes its way into just about every stargazer's life.

The division of labor between them is blindingly clear. Refractors are clearly superior in small apertures and Newtonians are clearly superior in large apertures. There is some overlap, but it's pretty small.

There are some pretty nice 3-inch Newtonians, but it's really stretching the technology to its lower limit. And since they cost barely less than 3-inch achromats, why bother unless you're truly poor?

Conversely, there are some relatively affordable 6-inch achromats, but they're a whole lot clunkier than 6-inch Newtonians -- and suffer from tons of false color as well. So while 6-inch achromats have their devoted followers, they're unlikely to ever constitute a large fraction of the market for this aperture class.

By the time you hit 8 inches -- a fairly modest aperture for Newts and SCTs -- refractors have pretty much fallen by the wayside.

Most stargazers own at least one small scope and one large one. The small scope is extremely likely to be a refractor. The large one might be either a Newt or a catadioptric.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: SpooPoker]
      #6495428 - 04/29/14 09:54 AM

Quote:

Ouch, that is one heck of an error. What happens to the airy disc in a colorful achromat?




It is a large error but one must remember that would probably assume an even distribution of light across the visual spectrum as well as an uniform sensitivity of the eye across the visual spectrum. In reality, the eye's sensitivity is greater at the center and the light is not necessarily evenly distributed...

Another factor to be aware of is that chromatic aberration is measured in relation to the size of the Airy disk. That is why larger scopes have more chromatic aberration for the same focal ratio.

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Tony Flanders]
      #6495438 - 04/29/14 10:01 AM

Quote:

Yes, it certainly happens. But Newtonians and achromatic refractors being the two oldest effective designs -- and also the simplest -- either one or both makes its way into just about every stargazer's life.

The division of labor between them is blindingly clear. Refractors are clearly superior in small apertures and Newtonians are clearly superior in large apertures. There is some overlap, but it's pretty small.




I generally lump refractors in one group and reflectors/Catadioptric's in the second group. Refractors make the best small scopes, Cats and Reflectors make the best large scopes. There is some overlap because of ergonomics and cost but optically the advantages of a refractor are most valuable in the smaller apertures and their liabilities increase dramatically with increasing aperture. Cats and refractors.. it works the other way around.

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
Mark9473
Postmaster
*****

Reged: 07/21/05

Loc: 51°N 4°E
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6495458 - 04/29/14 10:14 AM

BillP nailed it in a recent post, IMHO:

Quote:

Refractors are just not picky about things...like a loyal dog they are always there and ready to please. Dobs are like cats...they'll warm up or listen only when they are good and ready. SCTs....don't know what kind of animal is that problematic




Post Extras: Print Post   Remind Me!   Notify Moderator  
Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6495507 - 04/29/14 10:49 AM

Quote:

Quote:

Ouch, that is one heck of an error. What happens to the airy disc in a colorful achromat?




It is a large error but one must remember that would probably assume an even distribution of light across the visual spectrum as well as an uniform sensitivity of the eye across the visual spectrum. In reality, the eye's sensitivity is greater at the center and the light is not necessarily evenly distributed...




Indeed! It's worth remembering that the Airy disk does in fact have colored fringes -- even in a perfectly color-free telescope. The Airy disk in red light is almost twice the size of the Airy disk in violet light. So if you could get a really good color photo of an Airy disk, it would look like a rainbow.

But as far as I know, nobody ever sees those colored fringes. That's partly because the light source is rarely bright enough to stimulate color vision and partly because the eye's sensitivity peaks so strongly at a fairly narrow range of wavelengths.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Tony Flanders]
      #6495540 - 04/29/14 11:03 AM

Quote:

Indeed! It's worth remembering that the Airy disk does in fact have colored fringes -- even in a perfectly color-free telescope. The Airy disk in red light is almost twice the size of the Airy disk in violet light. So if you could get a really good color photo of an Airy disk, it would look like a rainbow.

But as far as I know, nobody ever sees those colored fringes. That's partly because the light source is rarely bright enough to stimulate color vision and partly because the eye's sensitivity peaks so strongly at a fairly narrow range of wavelengths.




Tony:

Another factor to consider is that the human eye is not free of chromatic aberration but we learn early on to correct for it.. or so they say.

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
Mr. Mike
Pooh-Bah
*****

Reged: 11/08/05

Loc: Churchville, NY
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Tony Flanders]
      #6495557 - 04/29/14 11:10 AM

Quote:



Yes, it certainly happens. But Newtonians and achromatic refractors being the two oldest effective designs -- and also the simplest -- either one or both makes its way into just about every stargazer's life.

The division of labor between them is blindingly clear. Refractors are clearly superior in small apertures and Newtonians are clearly superior in large apertures. There is some overlap, but it's pretty small.

There are some pretty nice 3-inch Newtonians, but it's really stretching the technology to its lower limit. And since they cost barely less than 3-inch achromats, why bother unless you're truly poor?

Conversely, there are some relatively affordable 6-inch achromats, but they're a whole lot clunkier than 6-inch Newtonians -- and suffer from tons of false color as well. So while 6-inch achromats have their devoted followers, they're unlikely to ever constitute a large fraction of the market for this aperture class.

By the time you hit 8 inches -- a fairly modest aperture for Newts and SCTs -- refractors have pretty much fallen by the wayside.

Most stargazers own at least one small scope and one large one. The small scope is extremely likely to be a refractor. The large one might be either a Newt or a catadioptric.




Tony - perfect summation. Refractors over 6" arent even available let alone viable! Imagine the girth of a 10" refractor? That'd be comical.... you'd need a crane for a mount.

IMO, with smaller sizes as you said the refractors really shine versus the other types of scopes. More net light gathering & no obstructions. Once you get larger..yeah... Id have me a light bucket too


Post Extras: Print Post   Remind Me!   Notify Moderator  
orion61

*****

Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Mark9473]
      #6495601 - 04/29/14 11:30 AM

Quote:

BillP nailed it in a recent post, IMHO:

Quote:

Refractors are just not picky about things...like a loyal dog they are always there and ready to please. Dobs are like cats...they'll warm up or listen only when they are good and ready. SCTs....don't know what kind of animal is that problematic






BOY what a bunch of BALONEY!!
People that say things like that have either never looked through a Schmidt, or at least one built since the 90's.
All telescopes that are properly fabricated will show good images.
Cheap Achros suffer from bad QA.. just like my C6-R. I have had 3 of them, ranging from just acceptable to excellent.
I also have several Schmidt Cassigrains, The optical quality and contrast is night and day compared to scopes produced from the 70's through 80's. Old orange tube Celestrons are nearly good tho.
They are vastly easier to transport and use, also Astrophotography is made so much easier than other scopes
it is hard to explain.
Yes your 4" APO will out perform an 8" SCT, IF the SCT is an old Dynamax, or Meade built before the later 80's..
I have had APO's Dobs up to 18" and every type of SCT.
Modern Celestron C6 SCT's are fantastic, small scopes, contrast and Brightness is unbelievable! It easily performs to the level of my RV6 Newtonian.
Bottom line is you get what you pay for.


Post Extras: Print Post   Remind Me!   Notify Moderator  
schang
scholastic sledgehammer


Reged: 04/24/13

Loc: columbia, sc
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: orion61]
      #6495798 - 04/29/14 12:57 PM

Quote:

Quote:

BillP nailed it in a recent post, IMHO:

Quote:

Refractors are just not picky about things...like a loyal dog they are always there and ready to please.






BOY what a bunch of BALONEY!!
People that say things like that have either never looked through a Schmidt, or at least one built since the 90's.
All telescopes that are properly fabricated will show good images.
Cheap Achros suffer from bad QA.. just like my C6-R. I have had 3 of them, ranging from just acceptable to excellent.

Bottom line is you get what you pay for.



How convenient is this universal conclusion for this subject!


Post Extras: Print Post   Remind Me!   Notify Moderator  
Alan French
Night Owl
*****

Reged: 01/28/05

Loc: Upstate NY
Re: Achromats & Apochromats - Cutting Past The Hype *DELETED* new [Re: Tony Flanders]
      #6495906 - 04/29/14 01:42 PM

Post deleted by Alan French

Edited by Alan French (04/29/14 01:45 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
rsimpkins
super member


Reged: 04/11/14

Loc: Lehi, UT
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Alan French]
      #6496016 - 04/29/14 02:39 PM

I'm new here and very much a beginner. Had I known when I made the first post the discussion would become eclipsed by a debate over telescope types and poor seeing conditions in your garage, I would have never started it.

My apologies to everyone who has had to slew through this thread. I rather think we've seen the darker side of amature astronomy instead of its brighter points. The discussion has clearly lost focus. Insulting your fellow astronomer is certainly an aberration in and of itself.

Are there any more astronomy puns I can use? In my geek circles we would normally invoke Godwin's Law at this point. How does Nazi Germany relate to amature astronomy? http://en.wikipedia.org/wiki/Godwin's_law

I don't mean any offense, but I think the community needs to know how this beginner feels: In the future I will think carefully before posting anything in this forum again. It is clear many of you take it seriously. Very seriously. That's great! However, in a "beginner" forum please keep in mind that some of us are just here for fun. Not for debates on how clean a garage can get or how many telescopes "real" astronomers should own. It really lowers the fun factor and is quite demotivating.

If there is a forum mod in here, please consider locking this thread. It needs to stop growing needlessly.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Abhat
sage
*****

Reged: 12/14/13

Loc: Middletown, MD
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6496107 - 04/29/14 03:39 PM

I was a beginner not so long ago and I love these discussions. The amount of knowledge that flows through is mind blowing. What I learnt here in 6 months could have taken me 6 years to learn on my own.

I never felt intimidated by these heavy duty technical discussion even as a beginner. No forum is perfect but this is the best one out there.

Edited by Abhat (04/29/14 03:41 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
SpooPoker
sage
*****

Reged: 06/04/13

Loc: North Bay CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6496125 - 04/29/14 03:48 PM

I agree but it is important to note that people do care, which is why discussions and thread derails happen. Equipment is part of astronomy, since without it our knowledge of the firmament would be no better than that of our ancient ancestors whom first pondered the heavens.

Not sure anyone insulted anyone here, disagreeing with someone does not insinuate an insult in my opinion. The forum has pretty strict rules regarding mindless insults or derogatory statements aimed at belittling another for no other purpose than self gratification.

Despite the tangents to discussion, there is plenty a beginner can learn from this thread sifting through the details. The thread started on the achromat and apo is very valid, since both designs feature prominently on the market - as do other telescopes like DOB's, SCT's and so on.

In summary, from the thread:

Achromats are excellent instruments in the smaller aperture, larger aperture it becomes tough to control the secondary spectrum / color without resorting to very long focal lengths. Shorter focal lengths give nice wide fields and pretty views, but are inhibited by colors not focusing in the same place. APO's overcome this and thus are more versatile and show more detail. They are rightfully desirable in their aperture class - particularly for astrophotography and to a lesser degree, visual. The APO would be seen as a natural evolution over the achromat and it is the more ideal refractor of choice for most astronomical work. That they are very expensive, prohibitively so for most astronomers, makes them unattainable. Thus the achromat, even in sizes 4" - 6" is a natural "refractor" choice despite some limitations due to the design. This then leads to the other aspect of other telescopic systems - i.e. reflectors, catadioptric and so on....

Astronomers will try out different scope designs - and the achromat, apo and reflector scopes do end up in many hands simultaneously since both do different jobs exceedingly well. Most folks take a bite out of the various scope design pie at one point or another.

Other equipment also enters the fray because the 6" APO, as wonderful as it can be, is still a 6" scope. An 8" APO is not readily available on the market, a 10" APO an even more rare specimen. Achromats in the 8" plus category are possibly even more rare on the open market, available as only custom builds from companies like D&G and / or Istar. Mounting any 6" plus refractor is a major factor - ALT AZ or EQ mounts that can handle such rigs are heavy, bulky, and can cost more than the telescope itself. This is where other designs come into play, at least ergonomically. The performance comparisons between different designs fall into a separate category, and ultimately, could be considered gratuitous banter or a simple thread detail. Interesting to me personally, but probably moot point given any quality telescope will show its stuff.


Post Extras: Print Post   Remind Me!   Notify Moderator  
GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6496357 - 04/29/14 05:26 PM

I think free flowing discussions can have a lot of benefit to learning. But your point on the beginners forum may be correct. Long threads are ones that hit a controversial topic. Achromats vs Apochromats is a pretty controversial topic in telescope land

Post Extras: Print Post   Remind Me!   Notify Moderator  
Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: GOLGO13]
      #6497510 - 04/30/14 06:55 AM

Quote:

Achromats vs Apochromats is a pretty controversial topic in telescope land.




Odd, why should it be controversial? Achromats are cheaper and apochromats work better. Who could disagree with that?


Post Extras: Print Post   Remind Me!   Notify Moderator  
Dave Lee
sage


Reged: 02/14/13

Loc: Pinehurst, NC USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Tony Flanders]
      #6497552 - 04/30/14 07:50 AM

Quote:

Quote:

Achromats vs Apochromats is a pretty controversial topic in telescope land.




Odd, why should it be controversial? Achromats are cheaper and apochromats work better. Who could disagree with that?




But there is this 'question of degree' issue. While 'work better' is (in principle) quite quantifiable, the visual significance (as in quantification) is less clear. Targets have differing amounts of visual information in the unfocused areas, neither type of scope is perfectly color corrected, and most importantly not all 'colors are the same' when it comes to visual perception.

Plenty of fodder for dispute by internet discussion forum standards

dave


Post Extras: Print Post   Remind Me!   Notify Moderator  
csrlice12
Postmaster
*****

Reged: 05/22/12

Loc: Denver, CO
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Dave Lee]
      #6497611 - 04/30/14 08:52 AM

Don't want CA of any kind.....get a reflector.....

Post Extras: Print Post   Remind Me!   Notify Moderator  
Mark Costello
Post Laureate
*****

Reged: 03/08/05

Loc: Matthews, NC, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6497672 - 04/30/14 09:24 AM

Hello, rsimpkins. You're right, the thread you started got side-tracked into a debate on how good or bad achros are. I probably should have stayed out; but reading stuff like "achros are dead or no good" gets to me.

Here is your original post:

"I was at a star party recently and I got to look through two refractors made by Explore Scientific. One was a ES127CF 5" f/7.5 ED triplet refractor. The other was a AR127 5" f/6.5 achromatic doublet refractor. Both were pointed at Jupiter in semi-*BLEEP* seeing that was keeping both scopes at lower powers. In the doublet I noticed a deep violet color fringing effect dancing around Jupiter that, quite frankly, was rather annoying (at least to me). The triplet was rock solid and looked great. Really, really great.

I've read that acromats are prone to this violet color effect, something that apochromats apparently fix. What's the actual non-BS take on this? If one wants to avoid the violet blues, do they have to step up to a more expensive triplet? Or is it possible to get no-color views through the "right" achromat in the "right" configuration?

I know the answer is probably really complex. I've read a few articles on this subject that break out all these complex graphs and complicated scientific explanations. I'm searching for a simpler "usually right" answer. If someone ponied up the extra $$$$ to get an apochromat, do they get views that generally avoid the violet effect?

It would really be lame to spend $2500+ on an apochromat only to find out that the purple star eater is still there. Might as well buy a much cheaper achromat and learn to live with it. Thoughts?"


Obviously, an achro is not for you. As to the ES 127ED, the word here and elsewhere is that it's a good scope for visual use and doesn't show any purple haze on the planets. I have no personal experience with it; hopefully people who do will chime in. Also, other amateurs might come in and recommend other apos or ED refractors in the price range of the ES127ED....

Take care,


Post Extras: Print Post   Remind Me!   Notify Moderator  
Alan French
Night Owl
*****

Reged: 01/28/05

Loc: Upstate NY
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Tony Flanders]
      #6497678 - 04/30/14 09:24 AM

Quote:

Quote:

Achromats vs Apochromats is a pretty controversial topic in telescope land.




Odd, why should it be controversial? Achromats are cheaper and apochromats work better. Who could disagree with that?




Absolutely agree.

Not only do they work better, but they allow for much shorter focal lengths. The color in a 4"f/15 achromat is fairly obvious, while a 4" apochromat of less than half the focal length is essentially color free.

Such shorter instruments translate into better portability, and a much more versatile instrument. A 4" f/6 can provide wide field views of up to 4.3 degrees of sky and some of the best high power views for the aperture.

A ~90mm apochromat makes a marvelous "crossover" scope, suitable for observing the night sky, birds, and other creatures. A small, fast achromat shows obvious and intrusive color at higher powers on a bright, sunny day.

Clear skies, Alan


Post Extras: Print Post   Remind Me!   Notify Moderator  
Alan French
Night Owl
*****

Reged: 01/28/05

Loc: Upstate NY
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6497699 - 04/30/14 09:41 AM

Quote:

(in part)

I've read that acromats are prone to this violet color effect, something that apochromats apparently fix. What's the actual non-BS take on this? If one wants to avoid the violet blues, do they have to step up to a more expensive triplet? Or is it possible to get no-color views through the "right" achromat in the "right" configuration?






The simple answer to your question is that all achromats have "secondary color," the purple halo due to the out of focus red and blue ends of the spectrum. It is fairly innocuous in a 3" f/15, but increases as you move up in aperture. It also gets worse as the focal ratio decreases.

The only way to cure it is to buy an apochromat, or a Newtonian (the least expensive fix). Apochromats use either a fluorite element or a fluor-crown (fluorite containing glass) to better match the mating glass and reduce secondary color. Using three elements in the lens allows for better control of color and other aberrations, and somewhat faster focal ratios with fine images. Either a doublet or a triplet apochromat can work extremely well. There are also Petzvel designs, which have two widely separated doublets (with fluorite or fluor-crown elements).

Using two widely spaced doublets allows the focal plane to be flat, an advantage for photographers and low power visual observers. Objectives with closely spaced elements have curved focal planes.

Clear skies, Alan


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon_Doh
scholastic sledgehammer


Reged: 09/16/11

Loc: On a receiver's back
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Alan French]
      #6497719 - 04/30/14 09:53 AM

People do tend to have opinions about their equipment and not just opinions, but strong ones. But, those opinions are pretty much based on each person's individual experiences - with their equipment observing under conditions where they live. And therein lies the problem with why our opinions regarding the same type of telescope may vary sharply. I live under humid skies and refractors do better for me than SCT's. But, if I were observing under dry Arizona skies my experience would be different.

Then too there are differences between instruments due to quality control variances. I've posted before about getting lucky with an achro I once owned that was virtually CA free. Yet I'm not insensitive to CA because I've noticed it even in some APO's. So I may have a good achro and you may have one that blinds you with CA and we're going to have a difference of opinions about achros. Same with SCT's and reflectors. I've seen SCT's where the image they put up was mushy regardless of how long it cooled down or how well it was collimated. And I've looked through some where the image they put up would knock your socks off. The first time I saw Saturn through my Meade ACF that I had just collimated I was stunned. It looked like a photo out of the astronomy books. A friend of mine bought a C8 and we never could get it collimated. The images it produced were simply terrible. But based on that experience I would never say SCT's aren't capable of putting up sharp images nor would I say Celestron's are bad. I just recognize that there can be big quality variances from unit to unit with Chinese manufactured telescopes.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Alan French
Night Owl
*****

Reged: 01/28/05

Loc: Upstate NY
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon_Doh]
      #6497763 - 04/30/14 10:20 AM

An achromat can not be free of secondary color. The secondary color is an inherent property of the glasses used. If you know the glasses, you can quickly calculate it.

The designer can only control which colors come to the same focus, and the optician can only correct spherical aberration at a specific wavelength.

However, the appearance of the secondary color depends on exactly what wavelengths were brought to a common focus. Most achromats bring the blue F line (486nm) and the red C line (656nm) to the same focus.

Lenses with differing choices of which colors to bring to a common focus show secondary color differently. Its appearance also depends on a individual's color sensitivity. We recently heard a talk on planetary nebulae, and the speaker mentioned a lab they just did. Some participants could see the Balmer emission line at 410nm (violet). Others could not.

I've also noticed that the processing the visual image by the retina (which does a lot of work) and the brain is very adaptive. The color error of a 4" f/8 achromat that resided here for a while became much less intrusive with time behind the eyepiece. The obvious blue tint of a Solar Skreen white light filter is absent from my observing eye, yet intrusive through my non-observing eye.

Clear skies, Alan


Post Extras: Print Post   Remind Me!   Notify Moderator  
Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon_Doh]
      #6497783 - 04/30/14 10:31 AM

Quote:

People do tend to have opinions about their equipment and not just opinions, but strong ones. But, those opinions are pretty much based on each person's individual experiences - with their equipment observing under conditions where they live.




Maybe, for most amateurs. But the people in my office at Sky & Telescope review telescopes for a living. Dennis di Cicco has probably built more telescopes than most people on Cloudy Nights have seen in their lives. And Dennis has used ten times more telescopes than he has built.

Likewise, Alan French is a well-known telescope maker, and he judges telescopes for the Stellafane competition. So he's seen a scope or two -- or a dozen, a hundred, a thousand -- in his lifetime.

Doesn't stop people from having opinions. But it does give them a lot of perspective. In general, the more you know, the less strident your opinions are likely to be.

Tony Flanders
Associate Editor, Sky & Telescope


Post Extras: Print Post   Remind Me!   Notify Moderator  
GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Tony Flanders]
      #6497814 - 04/30/14 10:52 AM

All I am saying is this topic often comes up in the refractor forum, and often has long threads. I agree with what you say of course. I have owned both types (and enjoyed both types).

It's not as controversial as reflector vs refractor types of threads. But it's certainly debated quite a bit. Mostly cost vs performance tradeoffs, use of filters, focal ratio, etc.

I would not hesitate to recommend a beginner get a achromat as a first scope. I started with a 70mm F5 and then a 102mm F10. The 102mm was a great scope despite the purple haze.


Post Extras: Print Post   Remind Me!   Notify Moderator  
bremms
Carpal Tunnel
*****

Reged: 08/31/12

Loc: SC
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Alan French]
      #6497825 - 04/30/14 10:57 AM

I've been reading this thread for a while now. My most used scope is a Jaegers 6" F10 Achromat. It has a color, no doubt there. It also has a no perceptible SA, no zones and smooth surfaces. I've used a couple 5" APOs (Tak, AP) they have a little more contrast, however the 6" F10 goes just asdeep and shows a little more fine detail. I'd rather have a 5" APO, but I put my scope together for under $600 with a used AP focuser, and machined all the cells. Is a 5" APO worth 5-15x the price? Not for me.
For me it's cost. I'd love a 120-150mm APO. Can't justify it though.


Post Extras: Print Post   Remind Me!   Notify Moderator  
alnitak22
sage


Reged: 02/12/11

Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Tony Flanders]
      #6497830 - 04/30/14 10:58 AM

Quote:

Quote:

People do tend to have opinions about their equipment and not just opinions, but strong ones. But, those opinions are pretty much based on each person's individual experiences - with their equipment observing under conditions where they live.




Maybe, for most amateurs. But the people in my office at Sky & Telescope review telescopes for a living. Dennis di Cicco has probably built more telescopes than most people on Cloudy Nights have seen in their lives. And Dennis has used ten times more telescopes than he has built.

Likewise, Alan French is a well-known telescope maker, and he judges telescopes for the Stellafane competition. So he's seen a scope or two -- or a dozen, a hundred, a thousand -- in his lifetime.

Doesn't stop people from having opinions. But it does give them a lot of perspective. In general, the more you know, the less strident your opinions are likely to be.


Tony Flanders
Associate Editor, Sky & Telescope




Well said!


Post Extras: Print Post   Remind Me!   Notify Moderator  
GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Tony Flanders]
      #6497857 - 04/30/14 11:09 AM

Just to make sure I wasn't imagining things I searched the refractor forum for the past few years for topics with achro vs apo threads. There are a ton of them and most of them spanning 100+ posts.

Maybe it's not a debated topic with professionals...but here on CN it is. And there is nothing wrong with that from my perspective. That may even help some folks new to telescopes choose the right scope for their situation.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Alan French
Night Owl
*****

Reged: 01/28/05

Loc: Upstate NY
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: GOLGO13]
      #6497873 - 04/30/14 11:19 AM

It does, however, seem that such debates are not appropriate for the Beginners Forum. This is a place for new folks to get questions answered. There are more suitable places to debate "apochromat versus achromat" and "refractor versus reflector," if you like beating dead horses to death, at least.

Clear skies, Alan


Post Extras: Print Post   Remind Me!   Notify Moderator  
GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Alan French]
      #6497878 - 04/30/14 11:24 AM

Quote:

It does, however, seem that such debates are not appropriate for the Beginners Forum. This is a place for new folks to get questions answered. There are more suitable places to debate "apochromat versus achromat" and "refractor versus reflector," if you like beating dead horses to death, at least.

Clear skies, Alan




That I completely agree with. Unless it was a beginner asking what's the difference between an achromat and an apochromat.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Alan French
Night Owl
*****

Reged: 01/28/05

Loc: Upstate NY
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6497900 - 04/30/14 11:34 AM

Quote:

(in part)

I've read that acromats are prone to this violet color effect, something that apochromats apparently fix. What's the actual non-BS take on this? If one wants to avoid the violet blues, do they have to step up to a more expensive triplet? Or is it possible to get no-color views through the "right" achromat in the "right" configuration?






This was the heart of the original question, which can be quite factually answered in just a few posts. Yet the subject line inspired one of the usual "versus" debates, which, I think, only confused the issue.

Clear skies, Alan


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon_Doh]
      #6497911 - 04/30/14 11:39 AM

Quote:

People do tend to have opinions about their equipment and not just opinions, but strong ones. But, those opinions are pretty much based on each person's individual experiences - with their equipment observing under conditions where they live.




An important part of the equation is simply that we love our equipment and often we have a limited range of experience, our viewpoint is limited by our experiences. As I see it, the goal here is to "cut past the hype" and help someone who has limited experience with telescopes have an understanding of the whats and whys... reasonable expectations are the goal. As much as possible, we need to step away from our own preferences, our likes and dislikes and rather try to put our own experiences in a more objective, general context.

I thought Rsimpkins' comparison of the two fast 5 inch refractors was quite perceptive and in agreement with my experiences:

"One was a ES127CF 5" f/7.5 ED triplet refractor. The other was a AR127 5" f/6.5 achromatic doublet refractor. Both were pointed at Jupiter in semi-*BLEEP* seeing that was keeping both scopes at lower powers. In the doublet I noticed a deep violet color fringing effect dancing around Jupiter that, quite frankly, was rather annoying (at least to me). The triplet was rock solid and looked great. Really, really great."

There is a lot to discuss but I think that is a pretty good place to start and finish..

Understanding a bit about the optical reasons for false color, how it scales with aperture and focal length, knowing chromatic aberration is not necessarily a deal killer, that as perfect as they seem, apochromats are still seriously limited by the their aperture, that some find that filters can help reduce the effective of the chromatic aberration... these are all good things to address and understand...

Myself, I probably have a little broader experience base than many, I have owned well more than 100 telescopes and currently have around 20. And too, I have strong preferences in my choice of equipment but those preferences are based on lessons learned from owning a great many telescopes of all types and sizes.. I know what is right for me but I also know it is not necessarily right for the other person.. .

With this thread in mind, the other night I decided to compare my 100mm F/6 Orion Astroview Achromat with my TeleVue NP-101 apochromat viewing Mars and Jupiter. I also used two filters, the typical red filter for Mars (I think it's a number 26) as well as an Orion V-Block filter for the achromat. The views of Mars were of particular interest. The achromat showed a noticeable red haze around Mars at best focus but the ice cap and the major features were visible, there was definitely something to see and study. Adding the V-block reduced the haze substantially but it did not seem to increase the detail seen. The red filter had a similar effect. By comparison, the apochromat provided a cleaner, more jewel-like view of Mars, no defocused red light, the ice cap and the major features were somewhat more easily seen but the difference was that there other, more subtle low contrast features visible in the apo that were not seen in achromat. They were not easily seen but they were there to be seen.


In my mind, there are two important thing about a high quality apochromat like the NP-101. One is that perfection of the view, of the picture in the eyepiece. This may or may not necessarily translate into seeing significantly more and certainly there are far more affordable ways to view the same level of detail and contrast.

The other is the versatility of an apo. A long focal length achromat of equal aperture can provide very similar high magnification views but it will be 5 feet long, quite unwieldy, and not well suited for those wonderful low power views that only a smaller, fast refractor can provide.

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
Mike4242
Pooh-Bah


Reged: 11/02/11

Loc: Memphis, TN
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6497960 - 04/30/14 12:07 PM

I recently added a post to my blog reviewing the ES 127ED. I also have a post about the ES AR152 achromat. There are several planetary and lunar images from each scope for comparison.

http://onetreeobservatory.wordpress.com/

Edited by Mike4242 (04/30/14 12:08 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: GOLGO13]
      #6498000 - 04/30/14 12:33 PM

Quote:

Maybe it's not a debated topic with professionals...but here on CN it is. And there is nothing wrong with that from my perspective.




I guess. But in the final analysis, what can you say?

Me: The false color in an achromat is objectionable.
Him: No it's not.
Me: Yes it is.
Him: No it's not.

As a rule, that's what all those fancy words and endless discussions boil down to. Either X degree of false color bothers you or it doesn't.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Alan French
Night Owl
*****

Reged: 01/28/05

Loc: Upstate NY
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Tony Flanders]
      #6498017 - 04/30/14 12:42 PM

Tony nicely summarizes much of the argument. It's a lot like arguing about the best car - the choice is very subjective and a personal one. It is often something that is not dictated by facts alone.

I'll note that back in the 1960s, achromats, even with their secondary color, were considered by many to be the ultimate telescope, especially for lunar and planetary work. It was widely noted that they should be f/15 for minimal secondary color, and that color got more obvious as one moved up in aperture.

Today, we have an even better option - the apochromat - in a much more manageable and versatile package.

Clear skies, Alan


Post Extras: Print Post   Remind Me!   Notify Moderator  
bremms
Carpal Tunnel
*****

Reged: 08/31/12

Loc: SC
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Alan French]
      #6498086 - 04/30/14 01:15 PM

At a price. I've used an ES ar152 and a Celestron CR6. The ES152 has a good bit of secondary color. What one would expect from an F6.5. The CR6 a little less. My Jaegers 6" F10
has even less but it still has a lot of CA. CA bothers some and not others. The 6" F10 Jaegers is at the limit for me as an all around scope. It is amazing you can get a C6r for about $400 used. Will it show more than a $400 APO.. UHH yea if you can find a lousy 60-80mm APO for $400.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: bremms]
      #6498150 - 04/30/14 01:44 PM

Quote:

At a price. I've used an ES ar152 and a Celestron CR6. The ES152 has a good bit of secondary color. What one would expect from an F6.5. The CR6 a little less. My Jaegers 6" F10
has even less but it still has a lot of CA. CA bothers some and not others. The 6" F10 Jaegers is at the limit for me as an all around scope. It is amazing you can get a C6r for about $400 used. Will it show more than a $400 APO.. UHH yea if you can find a lousy 60-80mm APO for $400.




On the used market, $400 will buy you a Orion ED-100.

But it will also buy you an 10 inch or maybe even a 12 inch Dob, both of which will provide, clean, more detailed, color free views of the planets as well as going deeper than is possible with a 6 inch anything.

Myself, an apo is not a bargain unless one is photographing birds at long distances or something similar. An apo refractor is like a fine eyepiece, it is just a pleasure to use...

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
csrlice12
Postmaster
*****

Reged: 05/22/12

Loc: Denver, CO
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6498168 - 04/30/14 01:54 PM

To those of us who grew up in the 60's, Purple Haze had an entirely different meaning.......

Post Extras: Print Post   Remind Me!   Notify Moderator  
Ed Holland
Carpal Tunnel


Reged: 06/16/10

Loc: San Jose, CA and Oxford, UK
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: csrlice12]
      #6498223 - 04/30/14 02:23 PM

I think the debate over telescope designs and their merits is fine. However, since this is the beginner forum, it would be a shame if any aspect of the conversation inadvertently intimidated or otherwise put someone off owning an instrument and seeing the sky. Or coloured [sic] their judgements in a negative way about something they do use.

I didn't get into astronomy at first (despite a latent interest) because of the cost of equipment, the apparent limitations of what I could afford and a sense that it was a bit elitist. I'm better off now, older if not wiser, and choose to run this hobby in a frugal way, and accept the compromises that brings.

Mars was a cracking sight two nights ago in the 5" refractor.


Post Extras: Print Post   Remind Me!   Notify Moderator  
schang
scholastic sledgehammer


Reged: 04/24/13

Loc: columbia, sc
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Ed Holland]
      #6498540 - 04/30/14 04:53 PM

Quote:

I think the debate over telescope designs and their merits is fine. However, since this is the beginner forum, it would be a shame if any aspect of the conversation inadvertently intimidated or otherwise put someone off owning an instrument and seeing the sky. Or coloured [sic] their judgements in a negative way about something they do use.

I didn't get into astronomy at first (despite a latent interest) because of the cost of equipment, the apparent limitations of what I could afford and a sense that it was a bit elitist. I'm better off now, older if not wiser, and choose to run this hobby in a frugal way, and accept the compromises that brings.

Mars was a cracking sight two nights ago in the 5" refractor.



Same experience a few nights ago on my C102 f/9.8 on Mars. Like you, I did not own a scope till 2013, despite my latent interest in astronomy back in 1980. That is a long "latent" time due to work and family. As a newbie, I found that these discussions actually helped me in a way that I could not do it on my own. While these opinions and options may intimidate and put off equipment purchasing for a newbie, however, I think that should be the purposes of this forum, to provide info so that newbies can choose one that best suits him/her. I'd hate to buy a scope and found that I do not like it because of this and that, and had to sell it later simply because I did not know better. Sometimes, putting off buying decision is the best approach just so one can learn a little more and distill your thoughts about what you truly need.

As a result, I have not regretted one bit of my first two scopes bought roughly at the same time, a 10" Dob and a C90 Mak. They were what I need, and still are. They did not break my bank or cost me an arm and leg. I felt that astronomy hobby has never been a hobby for the elitists. I still remember back then when people ground their own mirrors, partly because they love the hobby, but to some extent, the equipment was quite expensive then by today's standards. Now a day, we still have a lot CNers doing this DIY thing, even though they can afford stuff.

Life is a compromise, things are relative, and resource is limited. If we understood these truly, then for everything we do, we should have a clearer state of mind.


Post Extras: Print Post   Remind Me!   Notify Moderator  
LDW47
scholastic sledgehammer


Reged: 03/04/12

Loc: North Bay,Ontario,Canada
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Alan French]
      #6498716 - 04/30/14 06:28 PM

Quote:

Tony nicely summarizes much of the argument. It's a lot like arguing about the best car - the choice is very subjective and a personal one. It is often something that is not dictated by facts alone.

I'll note that back in the 1960s, achromats, even with their secondary color, were considered by many to be the ultimate telescope, especially for lunar and planetary work. It was widely noted that they should be f/15 for minimal secondary color, and that color got more obvious as one moved up in aperture.

Today, we have an even better option - the apochromat - in a much more manageable and versatile package.

Clear skies, Alan


The arguments still stand as many don't want to spend $$$$ on an Apo for a little bit of color on the brighter objects, that many times is very, very minimal and at times are virtually non existent at least with my ST Achro's and mine aren't anything special.

Post Extras: Print Post   Remind Me!   Notify Moderator  
LDW47
scholastic sledgehammer


Reged: 03/04/12

Loc: North Bay,Ontario,Canada
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Ed Holland]
      #6498766 - 04/30/14 06:48 PM

Quote:

I think the debate over telescope designs and their merits is fine. However, since this is the beginner forum, it would be a shame if any aspect of the conversation inadvertently intimidated or otherwise put someone off owning an instrument and seeing the sky. Or coloured [sic] their judgements in a negative way about something they do use.

I didn't get into astronomy at first (despite a latent interest) because of the cost of equipment, the apparent limitations of what I could afford and a sense that it was a bit elitist. I'm better off now, older if not wiser, and choose to run this hobby in a frugal way, and accept the compromises that brings.

Mars was a cracking sight two nights ago in the 5" refractor.


The only intimidation to a beginner is people shooting down some pretty decent Achro's that provide pretty decent views by implying that very high priced Apo's are the one and only, but that only really applies when seeing is at it's best which is few and far between and then only on certain objects. We should impress upon most beginners to start out with lower costs and work in to the better equipment, if they even want to, after they have decided whether this great hobby is in fact their bag. Remember a Chevy will get you there the same as a Caddy but for a lot less $$ ! Many perfectionists are losing the concept of the word ' beginner ' and it's financial implications, for some money is no object right from the word go but I think that is the exception and not the rule ?

Post Extras: Print Post   Remind Me!   Notify Moderator  
Alan French
Night Owl
*****

Reged: 01/28/05

Loc: Upstate NY
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: LDW47]
      #6498780 - 04/30/14 06:56 PM

Quote:

Quote:

Tony nicely summarizes much of the argument. It's a lot like arguing about the best car - the choice is very subjective and a personal one. It is often something that is not dictated by facts alone.

I'll note that back in the 1960s, achromats, even with their secondary color, were considered by many to be the ultimate telescope, especially for lunar and planetary work. It was widely noted that they should be f/15 for minimal secondary color, and that color got more obvious as one moved up in aperture.

Today, we have an even better option - the apochromat - in a much more manageable and versatile package.

Clear skies, Alan


The arguments still stand as many don't want to spend $$$$ on an Apo for a little bit of color on the brighter objects, that many times is very, very minimal and at times are virtually non existent at least with my ST Achro's and mine aren't anything special.




I agree. Secondary color is unnoticed on most objects in the night sky, especially in achromats of modest aperture. It is only evident, and intrusive to some folks, on the brighter celestial sights - the Moon and Jupiter make it most obvious.

The most cost effective instrument, though, remains the Newtonian reflector.

Clear skies, Alan


Post Extras: Print Post   Remind Me!   Notify Moderator  
Doc Bob
professor emeritus
*****

Reged: 02/27/09

Loc: Maryland, USA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Alan French]
      #6498839 - 04/30/14 07:24 PM

Very interesting commentary . . . I owned an ES AR 127 for the last 3 years; used a Baader SemiAPO filter and have had wonderful views of all things bright and a variety of DSO's! Color fringing was never a problem for me (filter helped) . . . but last week I traded up to the ES ED127 Triplet APO scope . . . blown away by the views! I never thought that there would be that much of a difference (ignorant me!). The one recommendation I can make is to attend any star parties in your area - most of us are happy to share views, and experience the variety of telescopes available. What you like is what you should stick with - it all depends upon what you like to observe!

Sorry for any rant and the crummy weather on the east coast secondary to my purchase!! The curse is real!!!

Good viewing,
Bob


Post Extras: Print Post   Remind Me!   Notify Moderator  
LDW47
scholastic sledgehammer


Reged: 03/04/12

Loc: North Bay,Ontario,Canada
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Alan French]
      #6498857 - 04/30/14 07:34 PM

Quote:

Quote:

Quote:

Tony nicely summarizes much of the argument. It's a lot like arguing about the best car - the choice is very subjective and a personal one. It is often something that is not dictated by facts alone.

I'll note that back in the 1960s, achromats, even with their secondary color, were considered by many to be the ultimate telescope, especially for lunar and planetary work. It was widely noted that they should be f/15 for minimal secondary color, and that color got more obvious as one moved up in aperture.

Today, we have an even better option - the apochromat - in a much more manageable and versatile package.

Clear skies, Alan


The arguments still stand as many don't want to spend $$$$ on an Apo for a little bit of color on the brighter objects, that many times is very, very minimal and at times are virtually non existent at least with my ST Achro's and mine aren't anything special.




I agree. Secondary color is unnoticed on most objects in the night sky, especially in achromats of modest aperture. It is only evident, and intrusive to some folks, on the brighter celestial sights - the Moon and Jupiter make it most obvious.

The most cost effective instrument, though, remains the Newtonian reflector.

Clear skies, Alan


I agree about the Newt / Dob but this post pertains to the Achro vs Apo so really the other types of scopes should not be part of the issue / discussion. This expansion occurs in many very specific / focused posts but in many cases maybe the poster already knows this aside type info and doesn't really care or it just adds to the confusion / means nothing.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Alan French
Night Owl
*****

Reged: 01/28/05

Loc: Upstate NY
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Doc Bob]
      #6498866 - 04/30/14 07:41 PM

Quote:

Very interesting commentary . . . I owned an ES AR 127 for the last 3 years; used a Baader SemiAPO filter and have had wonderful views of all things bright and a variety of DSO's! Color fringing was never a problem for me (filter helped) . . . but last week I traded up to the ES ED127 Triplet APO scope . . . blown away by the views! I never thought that there would be that much of a difference (ignorant me!). The one recommendation I can make is to attend any star parties in your area - most of us are happy to share views, and experience the variety of telescopes available. What you like is what you should stick with - it all depends upon what you like to observe!

Sorry for any rant and the crummy weather on the east coast secondary to my purchase!! The curse is real!!!

Good viewing,
Bob




Bob,

Another great point. There is absolutely nothing more beneficial than attending a star party or convention and seeing a variety of telescopes in person. Several decades ago this might have been a difficult task, but there are clubs all over, and almost every moonless weekend, at least in the warmer weather, sees a convention somewhere.

I suspect most folks could find a convention within driving distance, or a club close by.

Clear skies, Alan


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: LDW47]
      #6498894 - 04/30/14 07:54 PM

Quote:

I agree about the Newt / Dob but this post pertains to the Achro vs Apo so really the other types of scopes should not be part of the issue / discussion. This expansion occurs in many very specific / focused posts but in many cases maybe the poster already knows this aside type info and doesn't really care or it just adds to the confusion / means nothing.




This is the Beginners Forum, I think it is important to provide the full picture, the full context. The fact that a relatively inexpensive Newtonian can provide such excellent planetary views might "add to the confusion" but it a very real part of the picture and some mention is necessary.

Honestly, I would be very disappointed if someone were to read a thread like this one, spend $2500 on a 5 inch ED/apo and then setup next to someone with a $500 10 inch Dob and come to the realization that the $500 scope provided more detailed, clearer views of the planets. I don't want that to happen.

Doc Bob's recent post pretty much sums up the difference for me:

"Very interesting commentary . . . I owned an ES AR 127 for the last 3 years; used a Baader SemiAPO filter and have had wonderful views of all things bright and a variety of DSO's! Color fringing was never a problem for me (filter helped) . . . but last week I traded up to the ES ED127 Triplet APO scope . . . blown away by the views! I never thought that there would be that much of a difference (ignorant me!)."

That seems like a very real experience to me, it cuts through the hype and explains it in simple, understandable terms. A good quality achromat such as the ES127 can provide quite good views and quite satisfying views. But at the same time, the false color does detract from the image a telescope that puts essentially focuses all the colors to the same point, you see more.

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
LDW47
scholastic sledgehammer


Reged: 03/04/12

Loc: North Bay,Ontario,Canada
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6499031 - 04/30/14 08:58 PM

Quote:

Quote:

I agree about the Newt / Dob but this post pertains to the Achro vs Apo so really the other types of scopes should not be part of the issue / discussion. This expansion occurs in many very specific / focused posts but in many cases maybe the poster already knows this aside type info and doesn't really care or it just adds to the confusion / means nothing.




This is the Beginners Forum, I think it is important to provide the full picture, the full context. The fact that a relatively inexpensive Newtonian can provide such excellent planetary views might "add to the confusion" but it a very real part of the picture and some mention is necessary.

Honestly, I would be very disappointed if someone were to read a thread like this one, spend $2500 on a 5 inch ED/apo and then setup next to someone with a $500 10 inch Dob and come to the realization that the $500 scope provided more detailed, clearer views of the planets. I don't want that to happen.

Doc Bob's recent post pretty much sums up the difference for me:

"Very interesting commentary . . . I owned an ES AR 127 for the last 3 years; used a Baader SemiAPO filter and have had wonderful views of all things bright and a variety of DSO's! Color fringing was never a problem for me (filter helped) . . . but last week I traded up to the ES ED127 Triplet APO scope . . . blown away by the views! I never thought that there would be that much of a difference (ignorant me!)."

That seems like a very real experience to me, it cuts through the hype and explains it in simple, understandable terms. A good quality achromat such as the ES127 can provide quite good views and quite satisfying views. But at the same time, the false color does detract from the image a telescope that puts essentially focuses all the colors to the same point, you see more.

Jon


Maybe the poster is aware of the Newts / Dobs capabilities already so is not interested / concerned about them ? In fact they appear, in this post, to only be concerned about the Achro vs Apo issue so why throw in, in this case, superfluous, non applicable info ? As I said this happens all the time so no wonder some of these posts continue over multi pages and in the end completely diverge from the original issue. It all depends on the original post as to where it should go and where it should stay don't you wholeheartedly agree ? LOL !

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: LDW47]
      #6499046 - 04/30/14 09:05 PM

Quote:

Maybe the poster is aware of the Newts / Dobs capabilities already so is not interested / concerned about them ?




Maybe Rsimpkins was well aware of the capabilities of a Newtonian (MAKS and SCTS too) as a planetary scope but maybe he wasn't. And maybe others reading this thread are not aware of the bigger picture.

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
LDW47
scholastic sledgehammer


Reged: 03/04/12

Loc: North Bay,Ontario,Canada
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6499138 - 04/30/14 09:47 PM

Quote:

Quote:

Maybe the poster is aware of the Newts / Dobs capabilities already so is not interested / concerned about them ?




Maybe Rsimpkins was well aware of the capabilities of a Newtonian (MAKS and SCTS too) as a planetary scope but maybe he wasn't. And maybe others reading this thread are not aware of the bigger picture.

Jon


I guess I have lost / misunderstood the real meaning / focus of these issue specific posts ? And so it never ends ! My apologies !

Post Extras: Print Post   Remind Me!   Notify Moderator  
Kavenga
member


Reged: 02/25/12

Loc: SF Bay Area, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: LDW47]
      #6499323 - 04/30/14 11:13 PM

I have found this thread to be very informative and interesting. I am a beginner and this thread has enlightened me much. I currently have a 4.5" newt and was considering an ST-80 on the low end and a Barska Magnus 80ed on the high end if I can stretch my budget for a second (third) scope. I had a Tasco with a wobbly tripod and bad eyepieces as a kid.

I'd love a 10"+ newt; but, at this point a grab and go astro/terrestrial scope would be better for me. The light bucket will come...

There is a lot of food for thought in this tread. I even started looking at long achromatic telescopes in a more positive light.


Post Extras: Print Post   Remind Me!   Notify Moderator  
LDW47
scholastic sledgehammer


Reged: 03/04/12

Loc: North Bay,Ontario,Canada
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Kavenga]
      #6499396 - 04/30/14 11:57 PM

Quote:

I have found this thread to be very informative and interesting. I am a beginner and this thread has enlightened me much. I currently have a 4.5" newt and was considering an ST-80 on the low end and a Barska Magnus 80ed on the high end if I can stretch my budget for a second (third) scope. I had a Tasco with a wobbly tripod and bad eyepieces as a kid.

I'd love a 10"+ newt; but, at this point a grab and go astro/terrestrial scope would be better for me. The light bucket will come...

There is a lot of food for thought in this tread. I even started looking at long achromatic telescopes in a more positive light.


There are many, many beginners and experienced observers alike that have nothing but good things to say about the Orion or Sky Watcher ST80A, ST refractors performance and Grab & Go characteristics. I have a 102mm Antares ST and a SW 120mm ST refractors, both achro's and they to provide awesome, low power views on those great seeing nights. You surely don't have to spend a lot of $ to get some pretty decent views of the moon, planets and DSO's alike when night sky conditions are at their best. CA on the brighter objects can be compensated for through the use of reasonably priced filters.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: LDW47]
      #6499465 - 05/01/14 01:25 AM

Quote:

There are many, many beginners and experienced observers alike that have nothing but good things to say about the Orion or Sky Watcher ST80A, ST refractors performance and Grab & Go characteristics. I have a 102mm Antares ST and a SW 120mm ST refractors, both achro's and they to provide awesome, low power views on those great seeing nights. You surely don't have to spend a lot of $ to get some pretty decent views of the moon, planets and DSO's alike when night sky conditions are at their best. CA on the brighter objects can be compensated for through the use of reasonably priced filters.




Well... This is what this thread is about. I say a lot of good things about ST-80s, about 102mm F/5's and 100mm F/6 achromats.. They are rugged, affordable scopes that do a good job at low magnifications, a decent job in the mid ranges, and the chromatic aberration is most problematic at higher magnifications, observing the planets, splitting challenging double stars. Realistically, one should not expect for an F/5 achromat such as these to provide the same detailed views of the planets, split the same doubles, that an ED or apo scope would.

I own an ST-80, I actually own 2. They are what they are, if someone is looking small compact scope and has a specific interest in viewing the planets, I would not recommend an ST-80 or any F/5 achromat, filters or no filters, this is not their strength..

This is a fine line to walk. On one hand, I am one who believes that you use what you have and that whatever you have (or I have). If I happen to be out enjoying my ST-80, I will point it at Jupiter, at Saturn, at Mars, a Rigel, at Delta Cygni.. I have yet to split Rigel with a 80mm or 100mm fast archromat, I have yet to split Delta Cygni with the same scopes.. These are relatively easy in an 80mm ED/apo.

"Don't let what you can't do interfere with what you can do."

But I also think it is important share that information and experiences so someone who has a limited amount of experience can have realistic expectations, an idea of what they are buying and what to expect.

I point my ST-80 at Jupiter and Mars and see what I can see. There is no doubt I see more when I point my 80mm apo at Jupiter and Mars.. that's just how it is..

Jon


Post Extras: Print Post   Remind Me!   Notify Moderator  
alrosm
professor emeritus


Reged: 07/27/10

Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6499528 - 05/01/14 02:15 AM

You did the right thing when you went to a star party, judge for yourself and know what you really like, in fact, take your time and to try to go to more star parties to see many more refractors before you finally decide what refractor you want to buy.

Post Extras: Print Post   Remind Me!   Notify Moderator  
areyoukiddingme
sage
*****

Reged: 11/18/12

Re: Achromats & Apochromats - Cutting Past The Hype new [Re: alrosm]
      #6499572 - 05/01/14 03:41 AM

This hobby is all about trade offs, so I am all for addressing what the different scopes can do. It took me awhile (3-4 years ago) when I was beginning to realize this. A thread that brings up these trade-offs would have been a real eye opener to me. . . So I am glad to hear that the Dobs have been mentioned!

Post Extras: Print Post   Remind Me!   Notify Moderator  
LDW47
scholastic sledgehammer


Reged: 03/04/12

Loc: North Bay,Ontario,Canada
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Jon Isaacs]
      #6499706 - 05/01/14 07:58 AM

Quote:

Quote:

There are many, many beginners and experienced observers alike that have nothing but good things to say about the Orion or Sky Watcher ST80A, ST refractors performance and Grab & Go characteristics. I have a 102mm Antares ST and a SW 120mm ST refractors, both achro's and they to provide awesome, low power views on those great seeing nights. You surely don't have to spend a lot of $ to get some pretty decent views of the moon, planets and DSO's alike when night sky conditions are at their best. CA on the brighter objects can be compensated for through the use of reasonably priced filters.




Well... This is what this thread is about. I say a lot of good things about ST-80s, about 102mm F/5's and 100mm F/6 achromats.. They are rugged, affordable scopes that do a good job at low magnifications, a decent job in the mid ranges, and the chromatic aberration is most problematic at higher magnifications, observing the planets, splitting challenging double stars. Realistically, one should not expect for an F/5 achromat such as these to provide the same detailed views of the planets, split the same doubles, that an ED or apo scope would.

I own an ST-80, I actually own 2. They are what they are, if someone is looking small compact scope and has a specific interest in viewing the planets, I would not recommend an ST-80 or any F/5 achromat, filters or no filters, this is not their strength..

This is a fine line to walk. On one hand, I am one who believes that you use what you have and that whatever you have (or I have). If I happen to be out enjoying my ST-80, I will point it at Jupiter, at Saturn, at Mars, a Rigel, at Delta Cygni.. I have yet to split Rigel with a 80mm or 100mm fast archromat, I have yet to split Delta Cygni with the same scopes.. These are relatively easy in an 80mm ED/apo.

"Don't let what you can't do interfere with what you can do."

But I also think it is important share that information and experiences so someone who has a limited amount of experience can have realistic expectations, an idea of what they are buying and what to expect.

I point my ST-80 at Jupiter and Mars and see what I can see. There is no doubt I see more when I point my 80mm apo at Jupiter and Mars.. that's just how it is..

Jon


You are absolutely correct but why do we always skirt around / keep hidden in the background the huge, huge difference in price between the very capable Achro and a more capable Apo. You mention other times buying a used Apo, first many, especially beginners, may not want to take the chance with a used scope, secondly in many areas of the country good used scopes are scarce and the ones that do come up are snatched up pretty fast and thirdly most of them are advertised at prices almost new and in most cases does not include a decent mount that will cost many hundreds of $ more to get a decent one. For most new people entering this great hobby it is / would be pretty intimadating in itself dealing with a " buyer beware " situation when you don't really know what it's all about. In my opinion and mine only the huge price difference is as important as the additional benefits of the Apo that only really counts when sky conditions are at their best. This can be few and far between especially lately for many. To many long time experts that own a few of the higher priced scopes they are looking at / answering many of these beginner posts in their own mind set and many times cost is not a big factor, let's be honest but for a beginner it may be everything and may defer getting into this hobby if they get the impression that it is only worthwhile if you spend big $. So maybe we should put / stress this wide cost differential right up front vs in many cases benefits that don't mean that much to a beginner that just wants to look up into the night sky, right from the start of these great discussions as it is a big, big factor ? I mean, as with most of us, half of the fun / interest is buying, learning, knowing what you want / need and upgrading / accumulateing as we work along this hobby. Just my thoughts from past observations and I don't think I am too far off but no offence meant ?

Edited by LDW47 (05/01/14 08:36 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
rsimpkins
super member


Reged: 04/11/14

Loc: Lehi, UT
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: LDW47]
      #6500522 - 05/01/14 03:12 PM

Beginners are like snowflakes. Each one is different. A few more ideas came to my mind...

I have lots of really basic and stupid questions to ask and don't know which items are controversial. I recently learned that I am walking through a field of landmines without a metal detector. Whoops! Some questions are difficult to answer on my own. Cloudy Nights seems like the perfect place to get some of those questions answered. Independent of my personal feelings, this is a public forum. That means we all have some responsibility to those that follow us. The public and beginners would both be better served if the focus wasn't on informing the public in a general sense and instead focused on the needs of the snowflake: The actual beginner.

So what does a snowflake need? Each snowflake is different, and so will need different things. Have you noticed? No one has asked me why I'm interested in these types of telescopes. Hardly anyone has sought additional clarification. No one bothered to ask what my budget is, or if I've considered newtonians, or anything. No one bothered to figure out what kind of snowflake I am so they could best help. I came here looking for mentorship and guidance. Instead I ended up sidelined in the discussion as the heavy-weight astronomy gurus duked it out. This is lunar-cy (gee I love the puns in this hobby).

Maybe I can help make the community even better than it is. Perhaps one approach might be to make each thread a conversation with the beginner(s). If there are guru-level disagreements, take them to PM or a specialized forum. Work out the expert response and then update the beginners with what was agreed on by the gurus.

Alan French's "simple answer to your question" post was exactly what I was looking for. It was short, sweet, and directional. It put me on the right path to discover more about achromats and apochromats. Better would be if he pointed me to additional beginner level information or books (which he did in PM). Even better would be if he asked additional clarifying questions about why I'm interested in these two types of telescopes to begin with. An acro and apo weren't the only scopes at the star party I was at. No one asked: "What else did you look through at the star party? What did you see? What did you think?" Why didn't anyone ask me?

That is the single biggest piece of feedback I can give you all. Help beginners get engaged. Snowflakes can be fragile and melt easily. When you ramp up the technical knowledge you can easily lose people. That said, if a beginner shows up with an uncommonly deep technical knowledge then feel free to pepper that thread with all the jargon you know. Perhaps they are more of a snowball and less a snowflake. I am not easily scared away, but my first impression was that this forum wasn't as helpful as I hoped it would be.

It is much better to improve things by making a community better rather than just complaining. Can I help put together a "How To Help Beginners" sticky thread that encapsulates an approach experts can take to help beginners? It would be easy to log off and go do something else. I'm not going to do that because I think there is something special about the CN community. I think they can rise to the occasion.


Post Extras: Print Post   Remind Me!   Notify Moderator  
aa6ww
scholastic sledgehammer
*****

Reged: 10/23/11

Loc: Sacramento, Calif.
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: alnitak22]
      #6500533 - 05/01/14 03:19 PM

People that think chromatic aberration is all that maters in a refractor spend way way way way too much time in these forums and not enough time out under dark skies.

Learn the skies and whats out there, instead of acting like a 10 year old pointing your scope at only the brightest stars in the sky, and amazingly, the night sky becomes a beautiful play ground to enjoy, regardless of what type of scope you have in front of your face.

...Ralph
... Ralph


Post Extras: Print Post   Remind Me!   Notify Moderator  
REC
Post Laureate
*****

Reged: 10/20/10

Loc: NC
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6500555 - 05/01/14 03:29 PM

Yeah it's pretty amazing how a "newbie" question has 2,600 people reading it and 170 replies!

So in the end, have you decided what kind of scope your going to get and get out there under the stars?


Post Extras: Print Post   Remind Me!   Notify Moderator  
GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6500571 - 05/01/14 03:38 PM

Rsimpkins,

I don't think your original post warrented questions about your budget, had you considered newts, etc. It was a pretty focused question toward achros vs apos. It even says "cutting past the hype" (making it sound like it's something which is hyped) and spoke to why if apos are so expensive why people use them. We could have asked your budget or you could have stated it in the posting. Of course if you budget is $200 for the tube, then achro is the only way to go. If $800 was it there are many options for both designs.

I think the first bit of the posts were pretty good. As it kept going and people were having other conversations you may have asked for the topic to be locked if you didn't like the direction.

I would suggest next time making your title and question more geared to what you are looking for. Most of us really are trying to help. But also realize this is a group of many folks from many backgrounds. Each of which has their own inter-personal communication skills. I find that folks into astronomy/telescopes are not always the best socialially.

Quite frankly you were already at a pretty good source for informaiton and finding out about different scopes (a Star party). I find Cloudynights is very much like a star party. And just like a star party you get good and bad advice. You just need to filter through it to find the good stuff.

All this being said, these types of discussions are not as common in the beginners forum and usually questions are answered pretty concise and fast. But achro vs apo is one of those topics that garner a lot of discussion.


Post Extras: Print Post   Remind Me!   Notify Moderator  
GOLGO13
Carpal Tunnel


Reged: 11/05/05

Loc: St. Louis area
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: GOLGO13]
      #6500612 - 05/01/14 03:56 PM

Based on your clarifying post. I really suggest getting the book Star Ware by Phillip Harrington. It's a bit of out date (2007) for some aspects of the book. Such as suggestions on specific equipment would not have new products in it. However, I find it's an excellent source for explaining all telescope designs and how to pick the one that is best for your situation. It's really good in my opinion and not boring to read as some of the telescope books can be. Or maybe it's not boring to me because I like the tech side of astronomy.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Ed Holland
Carpal Tunnel


Reged: 06/16/10

Loc: San Jose, CA and Oxford, UK
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6500622 - 05/01/14 04:03 PM

rsimpkins,

I think you made very good points about the perceptions of a beginner, how you would have preferred the thread to develop and feeling sidelined in your own discussion.

The APO vs Achro discussion, and others of a similar ilk, will continue ad-nauseum for the rest of time.

I hope you will be able to choose a telescope, enjoy it, and let it feed your interest in astronomy.

Cheers

Ed


Post Extras: Print Post   Remind Me!   Notify Moderator  
SpooPoker
sage
*****

Reged: 06/04/13

Loc: North Bay CA
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Ed Holland]
      #6500697 - 05/01/14 04:43 PM

For a true beginner choosing a first telescope, it is important a telescope is recommended for purchase that will show him/her a wide range of objects that look nice at the eyepiece. Nothing more is needed to start out with. As Jon suggested, beginners certainly do not need to get suckered into, based on popular opinion or gratuitous vainglory, purchasing a 4” or 5" APO. The 5" APO is a versatile and great instrument, but a beginners scope, a first purchase? Hummmm….

I saw a thread regarding eyepiece advice with a beginner looking for eyepieces to use with his scope, and the recommendations coming in for ultra-rare (and expensive) vintage pieces made me tear my hair out. It is important to help newbies in the hobby find their way around to nice practical equipment, not get suckered into some niche corner of amateur astronomy where a said person would not get out of bed to look at the sky unless his/her collection of TMB supermono's or ZAO-II’s are inserted one at a time into their 7” Premium APO. Those astronomers, while welcome to their views, would better serve beginners by staying in their niche corner.

People should be responsible and give beginners good pragmatic advice. I always have a deep fondness for reading Jon’s postings – he keeps extremely level and practical, particularly with beginners. Jon will have his personal preferences, but leaves them on his sleeve understanding that “what works for one may not work for another”.

A good Achromat will certainly deliver, it is not junk compared to an APO. The inability to focus all wavelengths in the focal plane affects contrast and detail, but it is worth pointing out the effect is not dealbreaking at all – it is a small issue, not a gargantuan one. It is also worth remembering that for the longest while, achromats were considered the best telescopes, the cream of a small crop (before APO’s hit the scene and before the time where Newtonians with good mirrors and coatings started to surface).

In fact, for a beginner, I would scrap the entire concept of purchasing a high-end small to small’ish aperture refractor as a first venture into the hobby. 6"- 8” DOB’s are really good starting places (which is how a Newtonian can enter a refractor 1 vs refractor 2 conversation). Despite some folks experiences with 4” achromats/apo’s revealing better planetary detail than a typical stock 6” f/8 DOB or 8” f/6 DOB, there is far more in the sky than just planets, of which, only three are show stoppers (and one of those planets is only available for good views for a two to three month window every two years)! The difference between DSO’s in the eyepiece at 8” vs 4” is too large to even mention. A gray smudge to a 4” literally comes alive with 6 – 8” of aperture. To a beginner, this is all important. Anyone who understands this concept can see how a DOB can enter into an achromat Vs apo discussion in the beginners forum. In another forum, it may be seen as trolling / fanboyism to derail a thread. Over here, in beginners section, it should be considered acceptable.


Post Extras: Print Post   Remind Me!   Notify Moderator  
LDW47
scholastic sledgehammer


Reged: 03/04/12

Loc: North Bay,Ontario,Canada
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: GOLGO13]
      #6500744 - 05/01/14 05:04 PM

Quote:

Rsimpkins,

I don't think your original post warrented questions about your budget, had you considered newts, etc. It was a pretty focused question toward achros vs apos. It even says "cutting past the hype" (making it sound like it's something which is hyped) and spoke to why if apos are so expensive why people use them. We could have asked your budget or you could have stated it in the posting. Of course if you budget is $200 for the tube, then achro is the only way to go. If $800 was it there are many options for both designs.

I think the first bit of the posts were pretty good. As it kept going and people were having other conversations you may have asked for the topic to be locked if you didn't like the direction.

I would suggest next time making your title and question more geared to what you are looking for. Most of us really are trying to help. But also realize this is a group of many folks from many backgrounds. Each of which has their own inter-personal communication skills. I find that folks into astronomy/telescopes are not always the best socialially.

Quite frankly you were already at a pretty good source for informaiton and finding out about different scopes (a Star party). I find Cloudynights is very much like a star party. And just like a star party you get good and bad advice. You just need to filter through it to find the good stuff.

All this being said, these types of discussions are not as common in the beginners forum and usually questions are answered pretty concise and fast. But achro vs apo is one of those topics that garner a lot of discussion.


I agree 100%, we can lend advice based on experience but can't read minds. I don't think you would get any better info at any of the forums I have belonged to. We see so many varied posts that it is hard to determine exactly what beginners are looking for so you being new feel free to take it upon yourself to be more specific / focused in your queries. You have to expect technical answers from the highly technical people as part of their guidance if they don't know your real needs because there is just so much to learn where do we start.I think you got some good basic food for thought and an understanding of how complex this great hobby can be as you delve deeper into it ! Keep on asking and there is some good literature out there for beginners and two of the best, most comprehensive books are Night Watch and Backyard Astronomers Guide both written by the same highly regarded author. They are almost a must for any beginner wanting to learn all aspects of amateur astronomy not just how to find what is up there.

Post Extras: Print Post   Remind Me!   Notify Moderator  
schang
scholastic sledgehammer


Reged: 04/24/13

Loc: columbia, sc
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: rsimpkins]
      #6500745 - 05/01/14 05:04 PM

Your points are well taken...though the subject title was a little vague and subtle, which could be an easy bait and trap setup for the feeding frenzy crowd known as amateur astronomers.

Now, hope it is not too late...

What is your primary interests in the night sky?

What is your budget?

Please be specific, because a vague answer will not serve you well...


Post Extras: Print Post   Remind Me!   Notify Moderator  
Jon_Doh
scholastic sledgehammer


Reged: 09/16/11

Loc: On a receiver's back
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: Doc Bob]
      #6501871 - 05/02/14 08:44 AM

Quote:

Very interesting commentary . . . I owned an ES AR 127 for the last 3 years; used a Baader SemiAPO filter and have had wonderful views of all things bright and a variety of DSO's! Color fringing was never a problem for me (filter helped) . . . but last week I traded up to the ES ED127 Triplet APO scope . . . blown away by the views! I never thought that there would be that much of a difference (ignorant me!). The one recommendation I can make is to attend any star parties in your area - most of us are happy to share views, and experience the variety of telescopes available. What you like is what you should stick with - it all depends upon what you like to observe!

Sorry for any rant and the crummy weather on the east coast secondary to my purchase!! The curse is real!!!

Good viewing,
Bob




So, you're the reason I can't get a clear night!

Congrats on the new scope. A 5" APO is a wonderful instrument isn't it?


Post Extras: Print Post   Remind Me!   Notify Moderator  
LDW47
scholastic sledgehammer


Reged: 03/04/12

Loc: North Bay,Ontario,Canada
Re: Achromats & Apochromats - Cutting Past The Hype new [Re: aa6ww]
      #6501915 - 05/02/14 09:20 AM

Quote:

People that think chromatic aberration is all that maters in a refractor spend way way way way too much time in these forums and not enough time out under dark skies.

Learn the skies and whats out there, instead of acting like a 10 year old pointing your scope at only the brightest stars in the sky, and amazingly, the night sky becomes a beautiful play ground to enjoy, regardless of what type of scope you have in front of your face.

...Ralph
... Ralph


You hit it right on ! This is the key every time.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | (show all)


Extra information
17 registered and 35 anonymous users are browsing this forum.

Moderator:  WOBentley, kkokkolis 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 3514

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics