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Equipment Discussions >> Refractors

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Dubliner
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Reged: 05/01/12

Loc: Dublin, Ireland
Apochromatic or Achromatic does it really matter?
      #5210453 - 05/07/12 03:10 PM

Hello all,
Don't know if I'm in the right place for this question but I'll plough ahead regardless!
I know the basic differences between these lens types and you get what you pay for as as Apochromatic are multiples of the cost of an Achro scope.. But one of the main benifits
of Apros is their ability to eliminate (almost) false colour. So when it comes to imaging as most photos I see are in mono then surely there is no false colour and thus no need for such expensive optics? A 200$ scope would be as good as a $2000 scope? I speak only here of mono photos.
I must be misunderstanding something here and their is a big hole my reasoning?


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Thomas Karpf
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Reged: 02/09/09

Loc: Newington, CT
Re: Apochromatic or Achromatic does it really matter? new [Re: Dubliner]
      #5210512 - 05/07/12 03:57 PM

What sort of 'mono' photos are you planning on taking?

Imagine the light of a single star refracted through a lens. Let's consider three very specific wavelengths (deep red, green, and deep violet). The scope is focused so the green is in focus.

With an achromat, you would see a green dot in the middle, and a single ring around the star composed of red and violet. Focus on the red, and you have two concentric rings around the red dot, first the green and then the violet.

With an apochromat, those all three colors focus on that single dot.

If you image using three specific filters, you need to make sure that you focus correctly for EACH wavelength one at a time. If you shoot it all at the same time on a 'black and white' sensor, you would see rings with the achromat, and none with the apochromat.

Does that make sense???


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hfjacinto
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Reged: 01/12/09

Loc: Land of clouds and LP
Re: Apochromatic or Achromatic does it really matter? new [Re: Thomas Karpf]
      #5210515 - 05/07/12 04:01 PM

Tom pretty much states it in the above.

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gillmj24
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Re: Apochromatic or Achromatic does it really matter? new [Re: hfjacinto]
      #5210529 - 05/07/12 04:06 PM

$2000 scopes are generally corrected to a much higher level for other aberrations than $200 scopes, so you are paying for more performance in other aspects, not just less color.

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Dubliner
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Reged: 05/01/12

Loc: Dublin, Ireland
Re: Apochromatic or Achromatic does it really matter? new [Re: gillmj24]
      #5210639 - 05/07/12 05:08 PM

Thanks all,
I was only speaking about single shot mono cameras - without filters.
So if I have got this straight then those colours red , green, violet are not focused exactly in achromat,that is why we see colour fringes. If I take a mono photo these colour fringes are not removed by virtue of the fact I am shooting in b&w...the image will not be perfectly sharp by still having this fringing albeit now in monochrome.
Ok, maybe I was just trying to console myself with a cheaper scope!


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spaulmac
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Reged: 03/31/10

Loc: Louisville, KY
Re: Apochromatic or Achromatic does it really matter? new [Re: gillmj24]
      #5210647 - 05/07/12 05:13 PM

A mono camera still "sees" all colors, but only records the b&w component of each color. As per Thomas' explanation, even a mono imager in an achromat would record a fuzzy image.

One instance I am aware of in which an achromatic lens might provide an acceptably sharp image is if some form of narrow band filtration were used before the imager. This can be the case for solar telescopes, such as Hydrogen Alpha models, which could use less well corrected objectives since they only have to focus a very narrow band of light.


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Jon Isaacs
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Re: Apochromatic or Achromatic does it really matter? new [Re: Dubliner]
      #5210659 - 05/07/12 05:27 PM

Quote:

Ok, maybe I was just trying to console myself with a cheaper scope!




You asked a good question... for visual use, achromats can provide very nice views and certainly offer a good value for your money. Apochromats provide about as perfect a view as is possible for those willing to pay for the perfection.

Jon

Edited by Jon Isaacs (05/07/12 05:28 PM)


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spaulmac
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Re: Apochromatic or Achromatic does it really matter? new [Re: Jon Isaacs]
      #5210673 - 05/07/12 05:39 PM

I'll second Jon's statement on the value of achromats for visual use. Until recently, I was still quite happily using as my primary scope the same Borg achromat I purchased 10 years ago.

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watcher
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Re: Apochromatic or Achromatic does it really matter? new [Re: spaulmac]
      #5211265 - 05/07/12 11:29 PM

I have seen some VERY nice photos shown at CN taken with Orion ST80's. if the optics are decent, it will just take more time and effort but it can be done.

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Al Miller
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Re: Apochromatic or Achromatic does it really matter? new [Re: Dubliner]
      #5211677 - 05/08/12 09:39 AM

Quote:

So when it comes to imaging as most photos I see are in mono then surely there is no false colour and thus no need for such expensive optics? A 200$ scope would be as good as a $2000 scope? I speak only here of mono photos.




I did some experiments with yellow and green filters recently (I intend to do more IF I ever get the time!). I found the Baader 495nm pass filter (Yellow) particularly useful even with color (OSC) imaging. It cuts the blue/violet halos around brighter stars and sharpens the image while not cutting the blues from the object much at all. On monochrome images stars are considerable sharper, and resolved. Check out the link to my previous post on this as it contains a comparative image of M42 and a UV scan of the filter showing the passed spectrum. This filter was used on my Orion ST-120 that produces a significant halo if no filter is used. Of course your $200 scope wont become a $2000+ scope but, it will take images of very good quality (and save you some $$$). If anything, it's a good start to imaging while you save for a higher quality scope.

Yellow Filters


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jrbarnett
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Re: Apochromatic or Achromatic does it really matter? new [Re: Dubliner]
      #5211770 - 05/08/12 10:42 AM

Excellent question. As with all excellent questions, the answer is "it depends". More precisely it depends on you, your preferences and tolerances, and the kinds of targets you like to observe most.

In general, an apochromat will show less false color than an achromat. Note, however, that precisely what constitutes an "apochromat" isn't settled, and many scopes that are dubbed "apochromatic" by their makers or branders, nonetheless show false color under certain circumstances (much like an achromat does).

Here are a few rules of thumb that may help you figure out if an achromat would be "good enough" for your preferences and tolerances:

First, if you plan on imaging with the scope, even if your eye doesn't see false color (defocused light of particular wavelengths haloing brighter targets) the more stringent electronic eye of the CCD chip likely will. Imagers typically rank freedom from false color high on their "wish list" for a refractor.

Second, in any refractor that is going to display visual false color, it will do so to a larger extent at higher rather than lower magnification. If you spend a lot of time at higher magnification (e.g., you spend a lot of time observing the planets and the Moon), you will likely see more false color than if you spend more time at lower magnification.

Third, for a given aperture, irrespective of design (apochromat or achromat) the propensity for false color drops as focal ratio grows. A 4" f/5 FPL-51 "apochromatic" triplet would be more likely to show false color than a 4" f/9 FPL-51 "apochromatic" triplet, all else being equal.

Fourth, false color is generally more apparent on brighter targets than dimmer. Planets, the Moon and second magnitude or brighter stars are much more likely to show false color than dimmer stars and DSOs.

Fifth, not everyone perceives color in the same way. I have a 105mm f/14.4 achromat that, to my eye, shows a very large amount of false color at magnifications above ~110x on brighter targets. Others who own this same model profess that it is visually color free. It's important to calibrate your own eyes' color sensitivity (by trying different refractors and experiencing false color first hand).

The right answer for me (but maybe not for you) is that quality is king. I would choose the refractor with the superior optical figure over the one with a more average quality figure, irrespective of whether the better quality optic was apochromatic or achromatic by design. So for me, apochromatic vs. achromatic matters only a little bit in the grand scheme of things.

Regards,

Jim


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clintwhitman
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Re: Apochromatic or Achromatic does it really matter? new [Re: jrbarnett]
      #5211827 - 05/08/12 11:15 AM

Very well put Jim,
It seems my eyes like to see color problems more than most. The other thing I have seen over the years. Objectives that are not collimated correctly and focusers that are not square can produce false color issues, especially in large diameter refractors of either type.
Clint


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BigC
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Re: Apochromatic or Achromatic does it really matter? new [Re: jrbarnett]
      #5211856 - 05/08/12 11:31 AM

In my casual experiments this past week with common filters from Celestron and Zhumell whilst viewing with a Meade 102 f7.7 achromat ,I found the darker filters regardless of color seemed to sharpen the Moon a bit compared with paler filters .I touched up focus every time the EP and filter was swapped.Sans filters i see a bright yellow or purple fringe at the edge of the Moon at higher powers although don't notice false colors on the face.The Moon may not be the best test subject since one can filter the image much more than the dimmer light from a typical DSO people want to image.

Hopefully soon I will find time to try imaging with my DSI Pro and color filters and achro.


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frolinmod
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Re: Apochromatic or Achromatic does it really matter? new [Re: BigC]
      #5211926 - 05/08/12 12:10 PM

When using an achromat,

The problem if you're using a B&W camera without color filters is that you're recording all colors at once, each color will focus differently and you'll get blobs for stars.

If you're using color filters, then each one will have a different focus position and need to be focused differently than the others. You then combine them and everything is in focus. Well, not quite! Each of the color filters does have some overlap with the others, so each one will still catch some unfocused light. And then there is the luminance filter which is (almost!) the same as no filter at all above. Once again, blobs for stars.

When using an APO, all the colors focus closer together (or very close) and you get tighter stars. That's why you want an APO for imaging.


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aa6ww
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Re: Apochromatic or Achromatic does it really matter? new [Re: Dubliner]
      #5212378 - 05/08/12 04:22 PM

Quote:

Hello all,
Don't know if I'm in the right place for this question but I'll plough ahead regardless!
I know the basic differences between these lens types and you get what you pay for as as Apochromatic are multiples of the cost of an Achro scope.. But one of the main benifits
of Apros is their ability to eliminate (almost) false colour. So when it comes to imaging as most photos I see are in mono then surely there is no false colour and thus no need for such expensive optics? A 200$ scope would be as good as a $2000 scope? I speak only here of mono photos.
I must be misunderstanding something here and their is a big hole my reasoning?




I've got plenty of refractors for a variety of difference uses and moods and sky conditions. My overall favorite however is my Celestron Omni 1500 F/5. Favorite in that I find myself wanting to take it out more and more, more so than even my largest Refractor or SCT's, even on dark nights where a larger scope would give me more deep space performance. The Scope is about the same length as my TSA-102, and easily mounts on my GP-DX, so despite it being so short, it really packs a big wallop on performance. These latest generations out of China have no spherical aberration at all, so star patterns are tac sharp right out to the edges, even with the latest generation of 100 deg field of view Ethos and ES eyepieces, and my 41 Pan.
It packs considerably more punch than my TOA-130 for most what I view, and does a nice job even on bright objects like Venus and Jupiter with an MV filter as well as splits stars well. Globulars and open clusters are beautiful, especially under dark clear sky's, and even a friend I observe with, with his NP-127 is impressed how how sharp stars are throughout the entire field of view.
There are times when I want more aperture, or more planetary performance, but I have those options also, with different scopes,. For crisp planetary view, my TOA naturally wallops the Achro Doublet, on just about every deep space object I can think of, aperture still rules and the 6" Achro is my preferred scope to bring out. Its also excellent with my SM-90 Cornoado Filter with my BF-15.
Pound for pound my 6" F/5 beats out my other scopes as my favorite scope this season.

...Ralph


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Fomalhaut
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Reged: 08/16/08

Loc: Switzerland
Re: Apochromatic or Achromatic does it really matter? new [Re: aa6ww]
      #5213220 - 05/09/12 05:36 AM

We tested a 150/750 Skywatcher Achro under 6.5m skies against my fluorite-triplet (below) and the Skywatcher was not only (brutally) outdone on Jupiter as target, but interestingly also (distinctably) on M13. Yes, the globular seemed twice as bright in the Skywatcher, especially when both instruments being slightly defocused, but in focus and at 70x - 90x the stars where so much less pinpoint in the achro than in the Apo that the latter one showed better definition (=> more perceptible single stars) also on this low-contrast-object.

By the way that's a thing many observers seem not to be aware of: GCs behave as low-contrast objects when it comes down to discern feeble stars at visual threshold within the contrast-lowering haze generated by a GC's many other stars below visual threshold...

The big relative advantage of an apo versus an achro: virtually each photon goes where it belongs to, thus not haunting the image by contrast-lowering haze.

IMO, a decent short focus-refractor is quite acceptable at low magnifications (exit-pupil ~4mm and above), but when it comes down to resolution on low-contrast detail, even a 30% smaller apo will best it under critical scrutiny, and not just on planets, but also on certain DSOs.

Chris


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Starhawk
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Re: Apochromatic or Achromatic does it really matter? new [Re: Fomalhaut]
      #5213403 - 05/09/12 09:40 AM

Yes, it matters. 130 mm with f/6.3 and no color with a sharp image is a planetary thru DSO observing, one shot color imaging, all in one dream scope. But that requires APO prescriptions.

-Rich


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oldmapman
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Reged: 08/05/11

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Re: Apochromatic or Achromatic does it really matter? new [Re: Starhawk]
      #5213415 - 05/09/12 09:48 AM

YES

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skyjim
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Re: Apochromatic or Achromatic does it really matter? new [Re: Fomalhaut]
      #5214165 - 05/09/12 04:53 PM

THats the wrong achro to test against, that skywatcher is like a color machine, somethiong like a good C6R or the AT152/CT152 would be a better sample of an achro to do that test with, these scope are way better than the Skywatcher 150 F5.
Jim


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ken hubal
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Re: Apochromatic or Achromatic does it really matter? new [Re: skyjim]
      #5214187 - 05/09/12 05:17 PM

Having owned a large number of apo's and achros, a well corrected long focus achro is well suited for serious visual planetary observing. For visual work, an apo is overkill.

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coutleef
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Re: Apochromatic or Achromatic does it really matter? new [Re: ken hubal]
      #5214198 - 05/09/12 05:26 PM

Quote:

Having owned a large number of apo's and achros, a well corrected long focus achro is well suited for serious visual planetary observing. For visual work, an apo is overkill.




i like using a fast apo for visual as it allows me to have large FOV and wide views a long achro could not give as well as nice high power views.


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gnowellsct
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Re: Apochromatic or Achromatic does it really matter? new [Re: coutleef]
      #5214200 - 05/09/12 05:30 PM

Incidentally the choice is not either-or. The intermediate state between apo and achro is ED doublet. These exist in various formulations, including the FS tak series (FS102, FS128, FS152).

I definitely think that the color correction of an ED doublet is worth the price. In fact, am thinking about getting ED binoculars, but sometimes I just wait for the feeling to go away.

Greg N


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Refractor6
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Re: Apochromatic or Achromatic does it really matter? new [Re: coutleef]
      #5214206 - 05/09/12 05:36 PM

Quote:

Quote:

Having owned a large number of apo's and achros, a well corrected long focus achro is well suited for serious visual planetary observing. For visual work, an apo is overkill.




i like using a fast apo for visual as it allows me to have large FOV and wide views a long achro could not give as well as nice high power views.





Bingo!...we have a winner!

Due to light pollution conditions around my place having a 120 f/7.5 apo for viewing the "brighter" targets at high powers at night or for going down to low powers for daytime use on a shorter tube easy to view through rock solid package has been a real pleasure.


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skyjim
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Re: Apochromatic or Achromatic does it really matter? new [Re: ken hubal]
      #5214245 - 05/09/12 06:04 PM

Agree a 6" F12 achro like the D&G would be real nice but I jjust dont have the mount for that scope as of yet, I went threw a few F8 and under achros to finally find one that had what I would consider decent optics, the current scope seems to hit it and its an F5.9, slighly better correction than the CR150 I had back 10 years ago and the CA is way better controlled. I still want the 6" F12 but maybe someday but have been more than pleased with the AT152, even on lunar the amount of CA on the limb is not all that bad, craters and mountain shadows are black and white, no blueish haylows and thats without any filters in line plus saturn has looked real well. It takes a slight back seat to my 7" mac but not by allot and on deep sky wide feilds its stunning. I have had a few apo's and ED doublets up to 5" but the 6" class is just a different veiw IMO.
Jim


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ken hubal
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Re: Apochromatic or Achromatic does it really matter? new [Re: skyjim]
      #5214315 - 05/09/12 06:56 PM

I've found that deep sky objects appear with better contrast in a long achro than in the much overhyped apo! The ONLY reason for an apo is to help keep the tube length manageable while maintaining decent color correction. Depth of focus which is important for close binary and planetary observation is sorely lacking in the fast apos.

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Refractor6
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Re: Apochromatic or Achromatic does it really matter? new [Re: ken hubal]
      #5214333 - 05/09/12 07:08 PM

Not so sure about that Ken? I've already had some truly wonderful views of tight doubles right up to 450 power combined with some stunning planetary/lunar/sunspot views with an ED doublet f/7.5 120mm scope.

And yes I too have owned LOTS of scopes including some fine long f/ratio achros in the past for comparison in regards to the views at the ep.


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ken hubal
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Re: Apochromatic or Achromatic does it really matter? new [Re: Refractor6]
      #5214377 - 05/09/12 07:33 PM

I'm sure!! I have yet to see one apo that can perform admirably as a "do everything scope"! The arguement now becomes one of personal subjectivity. As for your observation through a 120mm ED doublet, I too have had the same type of refractor and have since returned to classic long focus achros because they simply perform better, espescially for splitting close binaries. They also don't require the use of exotic eyepiece designs with six or more elements of contrast-reducing air to glass surfaces. The much overhyped apos are good for astrophotography, which I've spent much time with but, as I said previously, are overkill for visual. I'll go with a larger reflector for serious A.P. anytime over the smaller apos. I have yet to view through any apo that did anything better than my long focus achros! I've owned apos from Takahashi, A.P., William Optics and others and was simply unimpressed by their performance to cost ratio! The continued market hype behind apos is total, complete and utter nonsense!
CHEEERS!


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Refractor6
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Re: Apochromatic or Achromatic does it really matter? new [Re: ken hubal]
      #5214387 - 05/09/12 07:38 PM

Well as a pure visual observer too using nothing more complex than a well coated and well figured ED doublet we'll have to agree to disagree then on this matter Ken

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mikey cee
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Re: Apochromatic or Achromatic does it really matter? new [Re: ken hubal]
      #5214794 - 05/10/12 12:54 AM Attachment (53 downloads)

Ken I agree with you! It's all hogwash. Mars tonight thru my Istar 10" f/11 R30 at 815x looks exactly like Mars did in 2003 thru all those f/6 apos. Mike

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jmiele
Patron Saint?
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Re: Apochromatic or Achromatic does it really matter? new [Re: mikey cee]
      #5215207 - 05/10/12 10:37 AM

815x! I'll be over tonight.
Joe


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buddyjesus
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Re: Apochromatic or Achromatic does it really matter? new [Re: jmiele]
      #5215361 - 05/10/12 11:58 AM

cool joe, you can put your cot next to mine in his observatory. I am moving in. haha

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ValeryD
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Re: Apochromatic or Achromatic does it really matter? new [Re: ken hubal]
      #5215380 - 05/10/12 12:03 PM

Quote:


1. I have yet to view through any apo that did anything better than my long focus achros!

2. I've owned apos from Takahashi, A.P., William Optics and others and was simply unimpressed by their performance to cost ratio!

3. The continued market hype behind apos is total, complete and utter nonsense!
CHEEERS!




1. Any well executed 7" F/8 fluorite doublet will do any astro-work much better than any your achromat of the same aperture.

2. The key words are "performance to cost ratio". The same can be said about Chevy vs BMW vs Ferrari. You get what you pay for. Nothing new under the moon.

3. Just only your personal opinion on this question + opinions of thouse, who split your opinion on 2.


Valery.


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Jared
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Re: Apochromatic or Achromatic does it really matter? new [Re: ken hubal]
      #5215568 - 05/10/12 01:46 PM

Quote:

I've found that deep sky objects appear with better contrast in a long achro than in the much overhyped apo! The ONLY reason for an apo is to help keep the tube length manageable while maintaining decent color correction. Depth of focus which is important for close binary and planetary observation is sorely lacking in the fast apos.



I agree that there is no perfect scope, but a shorter tube is hardly the ONLY reason for an apochromat. In addition to a shorter tube, you get a scope that is usable for deep sky astrophotography, especially wide field astrophotography, as well as a scope that provides wonderful wide field views visually. At most apertures, you also get better color correction than is achievable with a reasonable focal ratio achromat. As far as depth of focus goes, I believe a two speed focuser pretty much eliminates that advantage. I know there are many that feel slower scopes have more stable views--don't want to open that can of worms. Suffice it to say that there is legitimate disagreement on that score.

Do long focus scopes (achromats or apochromats) have advantages? Certainly. Optical aberrations are minimized, fields are flatter, longer eye relief eyepieces can be used for planetary viewing, and, at the very least, the longer tube length gets the aperture above some of the ground-level seeing "muck". Do short focus apochromats have advantages beyond a shorter, more manageable tube? Again, I would say certainly. I listed several above. If you prefer the slower scope, more power to you, but there is more to an apochromat than just a short tube.


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skyjim
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Re: Apochromatic or Achromatic does it really matter? new [Re: ValeryD]
      #5215837 - 05/10/12 04:09 PM

Oh no here we go again, I thought pushing your products is for the Venders forum Valery!

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Jan Owen
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Re: Apochromatic or Achromatic does it really matter? new [Re: skyjim]
      #5215851 - 05/10/12 04:18 PM

...on the other hand, Valery's right...

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jrbarnett
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Re: Apochromatic or Achromatic does it really matter? new [Re: ValeryD]
      #5215853 - 05/10/12 04:20 PM

Bah! What do you know, Valery? You're only a respected optical designer with dozens of game-changing innovations under your belt!


- Jim

Edited by LLEEGE (05/11/12 12:52 PM)


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skyjim
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Re: Apochromatic or Achromatic does it really matter? new [Re: jrbarnett]
      #5216059 - 05/10/12 06:36 PM

This is really funny, I was only stating that he is pushing his refractor in a post, that was it, nothing to do with his optical expertice at all.

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PJ Anway
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Re: Apochromatic or Achromatic does it really matter? new [Re: Dubliner]
      #5216112 - 05/10/12 07:12 PM Attachment (32 downloads)

I had a Zeiss AS100 refractor for many years and thought it delivered outstanding images. Several years ago I got an offer to buy a Showa SD100 apo refractor. I decided to go ahead, purchase and compare the two. Both are 100mm f/10's.

Though the Zeiss AS is considered to be somewhat better than a normal achromat, using a leading "short-flint" element; compared to the Showa, it showed noticeable color; at least more than I had ever noticed before. I still have the Showa. Sometimes you have to compare to really see the difference.


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watcher
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Re: Apochromatic or Achromatic does it really matter? new [Re: PJ Anway]
      #5216208 - 05/10/12 08:24 PM

Quote:

I had a Zeiss AS100 refractor for many years and thought it delivered outstanding images. Several years ago I got an offer to buy a Showa SD100 apo refractor. I decided to go ahead, purchase and compare the two. Both are 100mm f/10's.

Though the Zeiss AS is considered to be somewhat better than a normal achromat, using a leading "short-flint" element; compared to the Showa, it showed noticeable color; at least more than I had ever noticed before. I still have the Showa. Sometimes you have to compare to really see the difference.




Patient says to the doctor: "Doc it hurts when I do this." Doctor says to the patient: " Don't do that!"


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PJ Anway
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Re: Apochromatic or Achromatic does it really matter? new [Re: watcher]
      #5216287 - 05/10/12 09:07 PM

Good one Joe!

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maknewtnut
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Re: Apochromatic or Achromatic does it really matter? new [Re: Jared]
      #5216438 - 05/11/12 12:11 AM

Jared and others...if one or a few choose to bring up tube length as an issue, let's discuss that. Take a good look at the pic of the 10" f/11. Can you even see the ground? No.

Any person considering a refractor NEEDS to consider focal length. Why? Because a vast majority of amateur astronomers will never even consider the sort of mount that is required to utilize these telescopes.

I know this is the refractor forum, and that the discussion revolves around the strengths and weakness of achromats and apochromats. Still, when looking at what is required to utilize a 10" f/11 refractor, all of a sudden a 10" Newtonian seems far more appealing....and no chromatic abberation to boot.

CA is an attribute of considerable contention to many. Juptier is not purple, and therefore should not appear awash in purple through the eyepiece to many. At 250mm, f/11 is far too fast to avoid considerable levels of CA. At that aperture one might have to get to f/18-20 or slower to even play on the same field as a 10" triplet at f/9.

Is tube length an issue. Absolutely!


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tmbuser6
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Re: Apochromatic or Achromatic does it really matter? new [Re: maknewtnut]
      #5216472 - 05/11/12 12:42 AM

"At that aperture one might have to get to f/18-20 or slower to even play on the same field as a 10" triplet at f/9."

You are being generous Mark. To equal the correction of a 10" triplet at f9, an achromat would have to be f/40 or a bit longer. I've used a 13" Clark refractor and a 10" f/12 D&G extensively to be bought for a local public observatory I spearheaded for the community years ago. FINE instruments, GRAND views. But views of bright objects like the Moon or Jupiter were still awash in violet haze like there was a black light on inside the tube. That is simply wasted light not given to the image and smears the contrast from being even better than what it is. Still, an apo of that size is unspeakably expensive. Sometimes one must resign to inevitability and give in to using a Wratten #11 or something. One can do a lot, lot worse, and few things in this life are as good as viewing through BIG GLASS.

Wayne


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Re: Apochromatic or Achromatic does it really matter? new [Re: maknewtnut]
      #5216616 - 05/11/12 06:45 AM

Quote:

I know this is the refractor forum, and that the discussion revolves around the strengths and weakness of achromats and apochromats. Still, when looking at what is required to utilize a 10" f/11 refractor, all of a sudden a 10" Newtonian seems far more appealing....and no chromatic abberation to boot.




Or a 12.5 inch or a 16 inch Newtonian on a Dob mount... that 110inch focal length requires a serious mount.

Jon


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plyscope
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Re: Apochromatic or Achromatic does it really matter? new [Re: Jon Isaacs]
      #5216649 - 05/11/12 07:41 AM

This is an interesting review by Phil Barker of New Zealand comparing a 102mm f9 fluorite doublet with a 5" f15 achromat. Two fine telescopes with different pros and cons.

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skyjim
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Re: Apochromatic or Achromatic does it really matter? new [Re: plyscope]
      #5216767 - 05/11/12 09:30 AM

I read threw this post and its like the same old story that goes round and round by the same old guys here on which is better and why, then the experts chime in and give you the brutal details of why achro just dont cut the bar. I forgot the newt lovers chime in as well. Some here have allot invested in there heard of scopes, have had many samples pass threw there hands, some happy with what the now own and some never happy then there are the die hard achro guys that from what I can see are ATM'ers that place many hours and time into there prise larger achro, hey these guy I have to give credit twards cause instead of wipping out a credit card they have year of hard work going into there scope and to me thats a labor of love for this hobby. Then there's the vendors that chime in, I thought they had there own forum but I could be wrong. It seems to me like there are some here that are just plain insulting in there delivery of replys and you guys know who you are but the bottom line is whatever one has for a scope if they use it and like its veiws they should be happy and remember this is only a hobby and the guys who take this hobby to a semi pro level dont even post in most of these forums, they use what they have or can afford and do there work, most of those folks dont even care which is better cause there not scopeaholicks like some on these forums. What realy matters is that you enjoy the veiws even if there is some CA and good well figured achro can give up some pleasing veiws, maybe not 100% perfect but if you have deep pockets that 99% can be gotten from the APO camp and there are a whole lot of scopes in between.

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Re: Apochromatic or Achromatic does it really matter? new [Re: skyjim]
      #5217006 - 05/11/12 12:03 PM

Good summation.

I think that second to looking at the sky,beating dead horses is a main interest.

Actually it is a toss-up with some if bragging about their gear isn't more appealing than using it.

Edited by BigC (05/11/12 12:05 PM)


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avarakin
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Re: Apochromatic or Achromatic does it really matter? new [Re: Dubliner]
      #5222739 - 05/14/12 08:48 PM

Quote:

Hello all,
Don't know if I'm in the right place for this question but I'll plough ahead regardless!
I know the basic differences between these lens types and you get what you pay for as as Apochromatic are multiples of the cost of an Achro scope.. But one of the main benifits
of Apros is their ability to eliminate (almost) false colour. So when it comes to imaging as most photos I see are in mono then surely there is no false colour and thus no need for such expensive optics? A 200$ scope would be as good as a $2000 scope? I speak only here of mono photos.
I must be misunderstanding something here and their is a big hole my reasoning?




Going back to original question:
Most of the time "mono" photos you see on Astrobin or Astrophotogallery are taken in Hydrogen Alpha (Ha) wavelength using narrowband Ha filters. For such images achro or apo does not matter because light hitting the sensor has the same wavelength, so one can focus even achro precisely and get perfect star shapes.

It is also possible to take several narrow band images of same object using other wavelengths, like same Ha and OIII and SII and combine them into a false color image. In this case focus will also be perfect because each wavelength can be focused separately.

One can also take a real mono picture with a mono CCD and in this case APO will produce a better image than Acro, but I dont think this technique is very popular.

So answer is: it depends on what you want to do.
I personally like the narrowband techniques I described above because they allow to cut through light pollution, so in this case apo vs achro does not matter.

As far as general statement: "200$ scope would be as good as a $2000 scope?" - it is possible if $200 scope is a reflector or Schmidt Newtonian, although I guess this is a wrong forum to post such an opinion Of course $2000 scope will have much better mechanical components(especially focuser) and fit and finish, but optically they would be very similar.

Alex


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brianb11213
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Re: Apochromatic or Achromatic does it really matter? new [Re: avarakin]
      #5223078 - 05/15/12 05:46 AM

Quote:

Most of the time "mono" photos you see on Astrobin or Astrophotogallery are taken in Hydrogen Alpha (Ha) wavelength using narrowband Ha filters. For such images achro or apo does not matter because light hitting the sensor has the same wavelength, so one can focus even achro precisely and get perfect star shapes.



A singlet lens would do just fine for monochromatic imaging. You'd have to refocus when switching filters whereas with a parfocal set & a reflecting scope, or a good apo, you might get away without.

Of course, with extra surfaces (four instead of two for a air spaced achromat, six in an air spaced or oil filled apochromatic triplet) there is opportunity for a designer to correct aberrations other than chromatic rather better than can be done with a singlet lens, and usually there is a compromise between complete correction of chromatic & spherical aberration ("on axis") with off axis aberrations (coma, astigmatism & field curvature). Every optical system is a compromise to some extent, & extra surfaces introduce more light scatter, making a very simple optical system critical for some applications e.g. a Lyot coronagraph despite the efficiency of modern lens coatings.

So far as ordinary visual astronomy is concerned, an achromatic doublet will be adequate, provided that the focal length is kept reasonably long. A triplet apo design allows a shorter focal length with colour correction as good or better than an doublet with a longer focal length (even when using special glass) & is consequently easier to handle as well as having a larger field.


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Re: Apochromatic or Achromatic does it really matter? new [Re: maknewtnut]
      #5223310 - 05/15/12 10:33 AM Attachment (47 downloads)

Mark you are dead on about needing a big mount. But as far as objectionable CA goes you couldn't be further from the truth. My lens must have one heck of a figure plus the R30 rating I've been told by Istar actually performs closer to a 35% reduction in CA. Sure there is CA there but nowhere near what I was expecting. I'd bet if I put a cardboard 8" aperture stop on there it would perform so well I wouldn't believe my eyes. Mike

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buddyjesus
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Re: Apochromatic or Achromatic does it really matter? new [Re: mikey cee]
      #5223444 - 05/15/12 12:12 PM

beautiful scope mikey

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bobhen
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Re: Apochromatic or Achromatic does it really matter? new [Re: mikey cee]
      #5223650 - 05/15/12 02:27 PM

Quote:

Mark you are dead on about needing a big mount. But as far as objectionable CA goes you couldn't be further from the truth. My lens must have one heck of a figure plus the R30 rating I've been told by Istar actually performs closer to a 35% reduction in CA. Sure there is CA there but nowhere near what I was expecting. I'd bet if I put a cardboard 8" aperture stop on there it would perform so well I wouldn't believe my eyes. Mike




The quality of the optical figure has nothing to do with CA.

There is also a post on the Yahoo refractor forum from a noted optical design (not Roland) where he states that Istar objectives are purchased from DKD in China and that R30 does not reflect a 30% reduction in CA. But that these lenses are designed to just shift the correction curve towards the Blue end of the spectrum. And that some improvement will be seen in the blue but there will be a worsening in the red-orange part of the spectrum. In other words, the amount of CA is the same its just shifted to another part of the spectrum.

And, that for planetary work, it is actually better to shift the correction towards the red end of the spectrum.

Nothing wrong with a nicely figured achromat but Question: if these lenses cost more than a standard achromat are they really worth the increase in cost over a standard design if the actual CA is the same?

Bob


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Re: Apochromatic or Achromatic does it really matter? new [Re: bobhen]
      #5223701 - 05/15/12 02:55 PM

"In other words, the amount of CA is the same its just shifted to another part of the spectrum"...where your eye is a lot less sensitive anyway.

A scope that reduces the amount of false color you can actually see is worth something. Apochromats aren't apochromatic. There isn't a refractor in existence that crosses every single visible wavelength at a single point. It's all a question of degree. How far apart are the crossings, and what wavelengths cross at or near the same focal point? "Apochromat" and "achromat" are just labels. What matters is what your eye or your CCD camera *sees*. I'd say the R30 strategy has as much promise and value as the correction strategy employed in the Takahashi TOAs. It's not a new strategy, by the way. The recent crop of 102mm f/7 doublets from WO, Orion, Stellarvue and others, also shifted color correction so blue and green crossed near the same point making red the odd man out.

Regards,

Jim


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bobhen
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Re: Apochromatic or Achromatic does it really matter? new [Re: jrbarnett]
      #5223771 - 05/15/12 03:32 PM

Quote:

"In other words, the amount of CA is the same its just shifted to another part of the spectrum"...where your eye is a lot less sensitive anyway.

A scope that reduces the amount of false color you can actually see is worth something. Apochromats aren't apochromatic. There isn't a refractor in existence that crosses every single visible wavelength at a single point. It's all a question of degree. How far apart are the crossings, and what wavelengths cross at or near the same focal point? "Apochromat" and "achromat" are just labels. What matters is what your eye or your CCD camera *sees*. I'd say the R30 strategy has as much promise and value as the correction strategy employed in the Takahashi TOAs. It's not a new strategy, by the way. The recent crop of 102mm f/7 doublets from WO, Orion, Stellarvue and others, also shifted color correction so blue and green crossed near the same point making red the odd man out.

Regards,

Jim




Whether you can see CA is somewhat irrelevant, its the lost information in the out of focus part of the spectrum that never reaches the eye that is important - whether you see that lost information as false out-of-focus-color or not.

So - if CA is the same in these lenses as standard Achromatic lenses visible, not visible, in the red, or in the blue would not the damage to the image in the eyepiece be the same?

Bob


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BillP
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Re: Apochromatic or Achromatic does it really matter? new [Re: jrbarnett]
      #5223778 - 05/15/12 03:36 PM

Quote:

It's not a new strategy, by the way.




I believe I read that Zeiss used to do this also. So a very old strategy.

FWIW, by looking at this chart, the human eye is very much more sensitive to blue+violet, compared to just red. Jupiter, Venus, Mercury, Moon, Uranus, Neptune should all be better visually I would think when the spectrum is shifted for better correction towards the blue. Mars and Saturn being the only ones where advantageous for a shift towards the red I would think (and maybe just Mars as Saturn is stronger in yellow-orange). I had a red-shifted achromat and this is how it played out for me. Never had a blue-shifted one though.


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ValeryD
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Re: Apochromatic or Achromatic does it really matter? new [Re: BillP]
      #5224079 - 05/15/12 07:37 PM

Quote:

the human eye is very much more sensitive to blue+violet, compared to just red. Jupiter, Venus, Mercury, Moon, Uranus, Neptune should all be better visually I would think when the spectrum is shifted for better correction towards the blue. Mars and Saturn being the only ones where advantageous for a shift towards the red I would think (and maybe just Mars as Saturn is stronger in yellow-orange). I had a red-shifted achromat and this is how it played out for me. Never had a blue-shifted one though.




This is true ONLY at VERY low illumination, when an eye can't really see colors - night vision.
When observing planets, they create at the eye's retina almost the same illumination level, as a day light. So, the color sensitivity curve is about the same as in a day light. And in this case better to have a red shifted achromat. AS Zeaiss semi-apos are not only semi-apo, they also somewhat red shifted - much better for planets.

Also, Saturn and Mars both are much more valuable for most planetary observers, than Venus, Mercury, Uranus, Neptune
together.

In any case, the color correction shift in achromat is an easiest deal - two radii change. Material and labor cost are ecaxtly the same as in any another achromat.


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MRNUTTY
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Re: Apochromatic or Achromatic does it really matter? new [Re: jrbarnett]
      #5224245 - 05/15/12 10:01 PM

Quote:

"the recent crop of 102mm f/7 doublets from WO, Orion, Stellarvue and others, also shifted color correction so blue and green crossed near the same point making red the odd man out.




Beautiful, I'm almost entirely blind to red. Finally it comes as an advantage.


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mikey cee
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Re: Apochromatic or Achromatic does it really matter? new [Re: ValeryD]
      #5224254 - 05/15/12 10:07 PM

Valery....What you say is exactly how my correspondance with Istar's Master Optician Zdenek went. As long as it "looks" less to me at a fraction of an apo I could care less. I'm as happy as a clam and that's really all that matters. To each his own.

Edited by mikey cee (05/16/12 02:10 AM)


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skyjim
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Re: Apochromatic or Achromatic does it really matter? new [Re: mikey cee]
      #5224417 - 05/16/12 12:01 AM

Mike, you are right on, but what I dont think Valery realizes is your scope started as an ATM project, you didnt buy it all together, yes some comapny made the lens but your scope is a labor of love and an excellent one at that but the APO Gods dont seem to understand that. Your scope looks and sounds excellent and I have seen most of your posts as you have built this scope, my hats off to you, excellent job!
Jim


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BillP
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Re: Apochromatic or Achromatic does it really matter? new [Re: ValeryD]
      #5225163 - 05/16/12 01:33 PM

Quote:

Quote:

the human eye is very much more sensitive to blue+violet, compared to just red. ...




This is true ONLY at VERY low illumination, when an eye can't really see colors - night vision...




Think you are mistaken. With Photopic vision (day adapted) the eye is more sensitive to violet+blue (410-500nm) as my original reference chart shows. With Scotopic vision (dark adapted) the eye has essentially no sensitivity to red (655-700nm). Here is a chart of both vision types overlayed - link. So just look at the amount of area under the two ranges (violet+blue = 410-500nm and red = 655-700nm). In either vision type there is more area under the violet-blue than red.

Edited by BillP (05/16/12 01:39 PM)


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Re: Apochromatic or Achromatic does it really matter? new [Re: BillP]
      #5269750 - 06/13/12 03:14 PM

Visually there's some difference between an Apochromat or Achromat refractor... putting scopes next to each other under the same conditions will show this in practice!
Going for an Apochromat makes sense if You're considering to try Your hand at some AP ... which most of us do ... sooner or later


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saemark30
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Re: Apochromatic or Achromatic does it really matter? new [Re: PJ Anway]
      #5269793 - 06/13/12 03:34 PM

What do you call a diffraction assisted lens code-named H-Bomb?

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ken hubal
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Re: Apochromatic or Achromatic does it really matter? new [Re: saemark30]
      #5269901 - 06/13/12 04:47 PM

I have yet to view through ANY apo that did anything better than my well corrected long focus achro! The continued market hype behind apos is nothing more than excellent comedy!

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Alan French
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Re: Apochromatic or Achromatic does it really matter? new [Re: ken hubal]
      #5270038 - 06/13/12 06:25 PM

Quote:

I have yet to view through ANY apo that did anything better than my well corrected long focus achro! The continued market hype behind apos is nothing more than excellent comedy!




You know, it's funny, Ken. It wasn't marketing hype that started folks buying scopes made by those folks in Rockford, Illinois - it was people seeing and using them under the night sky at various star parties and conventions.

Clear skies, Alan


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jmiele
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Re: Apochromatic or Achromatic does it really matter? new [Re: Alan French]
      #5270105 - 06/13/12 07:18 PM

While I agree with your logic Alan, I think the photographic benefits afforded us by Apo's was also a big contributed to their rise in popularity. There are many good long FL achromatic instruments out there as well. In the visible wavelengths anyway.

All that said, all my Apo's look best to me

Best, Joe


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ken svp120
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Re: Apochromatic or Achromatic does it really matter? new [Re: jmiele]
      #5270317 - 06/13/12 09:51 PM

I'm going to add my two cents by saying that a long achro might well be corrected as well as an apo but that the nice compact package of a modern apo makes such scope truly portable...you can take it to whatever dark skies you wish with very little transport worries and get phenomenal optical performance. Or, if permanently mounted, you can put it in a smaller facility. Yes, an apchromat definitely matters for more than one reason. Can you attain the same performance from an achromat...probably...but with the same functionality? I don't think so.

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watcher
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Re: Apochromatic or Achromatic does it really matter? new [Re: ken svp120]
      #5270338 - 06/13/12 10:03 PM

Portability and imaging have both led to the popularity of APOs. IMO if it were just the view that counted, they would never have amounted to more than the niche market that they have forced the long achro into. But the asteroid did hit, and the dinosaurs no longer rule the earth.

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Re: Apochromatic or Achromatic does it really matter? new [Re: watcher]
      #5270365 - 06/13/12 10:20 PM

I decided to split the difference and bought an ED doublet (most would call it a "semi-apo").

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Alan French
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Re: Apochromatic or Achromatic does it really matter? new [Re: Astropin]
      #5270372 - 06/13/12 10:26 PM

As far as long achromats go, the asteroid hit before the days of the apochromat. I think it would be fair to say that apochromats brought refractors back to life.

Clear skies, Alan

Edited by Alan French (06/13/12 10:33 PM)


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watcher
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Re: Apochromatic or Achromatic does it really matter? new [Re: Alan French]
      #5270401 - 06/13/12 10:45 PM

Oh yeah, I keep forgetting about those mirrored things taking over way back when. I tend to hang out here where the refractors still rule, and see my corner of the universe as "all there is".

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Maurice
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Re: Apochromatic or Achromatic does it really matter? new [Re: Jon Isaacs]
      #6076361 - 09/12/13 05:06 AM

Hi all, I know this is an old thread but maybe you can help me out.
Currently I have an WO 80 ED scope. I'm really satisfied with it, but after using it a couple of years now I'm in the "need" for a larger refractor to be able to distinqush one nabula from the other in light poluted skies.

I don't do AP, so an ED looks perfect for my needs. I also want a refractor, I love the views they provide.
This one is on my wish list: http://www.teleskop-express.de/shop/product_info.php/language/de/info/p4688_T...

But recently I came across a 6" achromat: http://www.teleskop-express.de/shop/product_info.php?products_id=2229#ebericht

I know this scope will give me some CA, but looking at the picture made with this scope (see user reports) I'm really impressed with the quality.

What do you think that suits my needs best (again, only visual observing), a 120 ED for 1700 euro or a 152 achromat for "only" 800 euro?


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Niklo
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Re: Apochromatic or Achromatic does it really matter? new [Re: Maurice]
      #6076384 - 09/12/13 06:13 AM

Quote:

Hi all, I know this is an old thread but maybe you can help me out.
Currently I have an WO 80 ED scope. I'm really satisfied with it, but after using it a couple of years now I'm in the "need" for a larger refractor to be able to distinqush one nabula from the other in light poluted skies.

I don't do AP, so an ED looks perfect for my needs. I also want a refractor, I love the views they provide.
This one is on my wish list: http://www.teleskop-express.de/shop/product_info.php/language/de/info/p4688_T...

But recently I came across a 6" achromat: http://www.teleskop-express.de/shop/product_info.php?products_id=2229#ebericht

I know this scope will give me some CA, but looking at the picture made with this scope (see user reports) I'm really impressed with the quality.

What do you think that suits my needs best (again, only visual observing), a 120 ED for 1700 euro or a 152 achromat for "only" 800 euro?



Hi Maurice,
the 6" achromat shows much details on the moon but it's probably taken with a green filter. In the green light the 6" is probably better than a 5" ED in green light but without filter you'll see color fringe in the 6" and then the 5" ED should be *better*.
The 6" achromat is probably mainly for deep sky with lower magnification, or for watching the moon or sun with filters, and not a ideal *planet refractor*. Probably it'll work with filters on planets, too, but I don't know if it's good enough for you (I have to say, that I never watched through this 6").
Clear skies,
Roland


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Sasa
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Re: Apochromatic or Achromatic does it really matter? new [Re: Maurice]
      #6076415 - 09/12/13 06:52 AM

Hi Maurice,

I had the two telescopes in hand (not exactly TS 120ED but Skywatcher ED120/900, my guess is that it houses the same optics). It is very hard to recommend one, it really depends on you preference.

The 120mm ED scope is very universal, it is capable of nice low power views but it is also very good on planets and observing at high magnifications.

But if your main target are just nebulae, as you write, TS 152/950mm Individiual is also very good choice. A friend of mine has it and we observed together one night. No planets or Moon, just DSO. I was however surprised by good quality of the optics. You could tell on globular clusters at power of about 180x that the stars were not that crisp as in my 100mm ED refractor, but the view was still very good - and how knows how much of this was just due to possibly worse seeing. The 150mm lens was also showing much more stars than my 100mm lens of course. This is in contrast with Skywatcher 120/600mm achromat that I was playing with couple of years ago. This one was not pleasing to my eyes on globulars already at power of about 80-100x. The Skywatcher was just a telescope for low power views. TS Individual is doing much better in this respect and works on DSO very well even at quite high powers.

So I would say, hard choice. If I were in your place I would probably choose ED120. Especially from light polluted sites, you can enjoy the planets and Moon as well in this scope even without filters.

Alexander


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Re: Apochromatic or Achromatic does it really matter? new [Re: Maurice]
      #6076579 - 09/12/13 09:14 AM

Hi there Maurice. Since your experience is with an ED refractor and you're considering a larger ED or even larger achromatic refractor (achro), let me suggest that you look at a couple of your favorite heavenly objects with an achro before making your choice. I have and regularly use a 5"F6.5 achro (it's my only scope) on the moon, a few planets, and a lot of deep sky objects (DSOs). I "tune out" the chromatic aberration but if I look for it, I can see it on the moon (only at the edge), the planets, and brighter stars. It doesn't bother me, but many people don't like it and you might not want to put up with it.

All the best in making your choice.


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Jeff B
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Re: Apochromatic or Achromatic does it really matter? new [Re: Maurice]
      #6076675 - 09/12/13 10:10 AM

Maurice:

If you have a mounting that can handle it, I can recommend a 6" f10 achromat as a great compromise between size, CA, spherochromatism, light grasp and large field of view.

They display low visible levels of CA at low to medium powers and the F10 stop is very "eyepiece friendly". You can also stop them down to 4 or 5 inches for high power work with greatly reduced CA.

I've had one in some form or another for decades. Just a wonderful and easy to use scope.

Istar makes a good one or you can try to snag a used Jaegers.

Jeff


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beanerds
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Re: Apochromatic or Achromatic does it really matter? new [Re: Jeff B]
      #6077740 - 09/12/13 09:14 PM

Great discussions going on here , I am enjoying it .
Here is my 5c worth, it is this , a good achromat will show all that an APO will but with a bit of CA on the brighter objects , that's life .

I had a NG 127mm triplet last year and it was very good ( but heavy ) and I sold it to buy my Tak M210 , I missed the 127 so much that I grabbed an Istar 127mm f8 achromat and built a scope around that objective , ( see my 'viewing sessions with 127mm Istar achromat' thread here ) and it performs 98% as good as the 127mm triplet I take off 2% because of the small amount of CA , that's all , I do like its views .

Now , last Saturday night I took my Istar f8 along to our dark sky night for the first time and a big ( 20 inch ) dob owner came over for a look at Venus thru my achro and his first words was 'Is this thing a triplet ?' , 'No' I said only an achro doublet , woaw !! he said , 'will you bring this along next time and I will bring my 127mm TV APO along so we can do a side by side' .
I cant wait for that , it will be interesting and I will keep you all posted as to how it turns out .
That's very high praise , indeed for my lowely old 127mm Istar f8 achromat .

If you cant afford 3-6k for a 100-150mm APO , a well made achro will satisfy nicely if used within its limits .

ps. I do like that TS 150mm f950mm achro , nice clooking scope that would perform very well , I think .

Brian.


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Maurice
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Re: Apochromatic or Achromatic does it really matter? new [Re: beanerds]
      #6078207 - 09/13/13 04:20 AM

Thanks for all the good advise, really appreciated. But I'm a bit more confused now
Although the 152 achro seems a very good deal to me, I'm concerned about how good it will be as an allround scope, especially in light poluted skies and how easy or hard it is to handle.

Furthermore, the achromat is way havier than the 120 ED, so part of the money I'll save on the achromat needs to be spend on a heavier mount. I was considering an iOptron MiniTower (II or pro? That will be the next discussion) but I asume that's out of the question for the 152 achromat.

Hmmmmm.... Tough decision, luckely I have some time to think it over since I have to take care of my bank account first

Likely I will settle for the 120 ED, for now it seems to me the most practical and user-friendly scope of the two and coming from a 80mm I believe it will still be an noticeable step up. At least that is what I hope to achieve...

Boy o boy, I don't know anymore. Our hobby is all about making tough decisions

Btw, unfortunately I am unable to look through any of these scopes prior to purchase because they are not present on the star parties I visit and the shop that sells them is too far away from where I live to visit them.

Edited by Maurice (09/13/13 04:35 AM)


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Kunama
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Re: Apochromatic or Achromatic does it really matter? new [Re: Maurice]
      #6078233 - 09/13/13 05:29 AM

If you're considering AP in the future I would suggest you get a 120mm ED scope rather than the 150 achromat. The biggest difference you will see will be on bright targets like Saturn, Jupiter, Luna, etc. You will also have a slightly wider view for clusters etc. The mount requirement for the 120 will be EQ5 equivalent or bigger, the 150mm will need EQ6 or bigger.

The 120ED will be fine on the iOptron MiniTower Pro but your AP options will be limited to short exposures due to field rotation when using an AltAz mount.

I am currently doing visual only and use a 120mm F7.5 (900mm fl) on a manual T-Rex mount and find that to be a fantastic setup for me.
My previous scope was a 150mm F10 Istar which is an excellent scope but does require an EQ6 mount as a minimum. The smaller diameter of my 120 is more than compensated for by the reduced extraneous colour of the better optical design (mine is a Tak TSA120 Super Apochromat)

Good luck with your choice.


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beanerds
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Re: Apochromatic or Achromatic does it really matter? new [Re: Maurice]
      #6078234 - 09/13/13 05:31 AM

Yes Maurice , its a tough decision , I know but mate its your money .

Just to put into some sort of perspective down here is Australia , our 'Ice in Space' classifieds , our local astro web site and it has 2 x 120mm refractors currently for sale ,

#1 is an Orion 120mm f8.3 achro , ( great scope ! ) for $100 aud .

#2 is a no brand ( probably a North Group and another great scope ) 127mm f7.5 triplet for $1800 aud .

Take your pick ? , if I was just starting out the $100 achro would be awesome , that's what you originally asked ? $200 vrs $2000 ? , stick it on an Astro Tech Voyager alt/az for another $279 aud ( Brand new ) and you are away with a great scope .

The triplet will fit on the AT voyager ,,, just ! but it will be a pain to use because the triplet's are 2x the weight of the achro's and it will wobble horribly . ( I have owned both , see above ), so you would need a HEQ5 ? type mount or HD alt/az mount for an already $1800 scope ??? ,,, its your money mate , but for starting out I would personally ( If I needed another 127mm achro ) grab the $100 scope and AT mount for a total of $379 , and be very happy with that set up too.

Look 2nd hand , there are some awesome bargains out there , like these two I have just mentioned .

Brian.


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Niklo
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Re: Apochromatic or Achromatic does it really matter? new [Re: Kunama]
      #6078269 - 09/13/13 06:23 AM

Hi Maurice,
the 6" 900 mm is very short so I think that the EQ6 is not a must. An Celestron ADM mount could be sufficient (haven't tested it) the EQ5 maybe a little bit too weak.
A 6" f/10 has a much longer lever arm and will require a more powerful mount than a 6" 900 achromat.

For the EDs there are cheaper versions of Skywatcher Equinox or Evostar ED 120/900. That could be an alternative that works well even for very high magnifications with an EQ5.

Cheers,
Roland


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Jon_Doh
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Re: Apochromatic or Achromatic does it really matter? new [Re: Niklo]
      #6078429 - 09/13/13 09:41 AM

Maurice, I have a 152 achro and it does very well for nebulae. The CA is not bad at all on the moon. I see a very thin yellow line that disappears when I shift my eyes. The detail on the craters is excellent and free of CA. CA is worse on Jupiter but it can mostly be removed with a Baader Fringe Killer filter. This filter also helps focus the stars tighter and improves contrast on the planets. You should get one and screw it onto your diagonal.

The downside to the achro is that they are huge, not so heavy as bulky. Because of their length when viewing something like M57 which is right at zenith now you have to sit on the ground. The 120 may be somewhat better in terms of viewing angles, but basically that's the cost of a refractor over a dob or sct.


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gdd
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Re: Apochromatic or Achromatic does it really matter? new [Re: Jon_Doh]
      #6078651 - 09/13/13 12:27 PM

If cost is a stumbling block and you wish to take black and white photos (not necessarily mono) you can use a light yellow or violet minus filter on the achro and get some nice shots. Doing this you will be taking black and white photos in red and green light and will not have blue/violet bloat around the brighter stars.

Using such a filter for visual just depends on your tolerance for a slightly dimmed yellow cast on all views.

Gale


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Jon_Doh
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Re: Apochromatic or Achromatic does it really matter? new [Re: gdd]
      #6078810 - 09/13/13 02:01 PM

For astrophotography the best results with an achro are obtained by stacking a Baader Fringe filter with their Skyglow filter. You'll get white stars with no yellow cast or purple halos. This combo really works nicely on the moon and Jupiter too for visual.

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PeterR280
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Re: Apochromatic or Achromatic does it really matter? new [Re: Jon_Doh]
      #6078821 - 09/13/13 02:08 PM

I think you still get a greenish tint with both filters. You can always correct the color in photoshop if there is a tint.

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jrbarnett
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Re: Apochromatic or Achromatic does it really matter? new [Re: Dubliner]
      #6078859 - 09/13/13 02:36 PM

Here's why it matters. No, it's not about chromatic aberration, or field of view, or anything else achromat and apochromat fans tend to argue about. Apochromats are better because of *economics*. Wha?

Yeah, that's right. The economics of making and selling apochromats favor superior quality. While it's true that low dispersion glasses cost more than traditional optical glasses, but this is greatly over-emphasized. Increased glass costs are only a small component of the increased relative cost of an apochromat over a similar achromat. Instead, because apochromats (fairly or not) are in higher demand. This means that manufacturers and dealers of such designs enjoy much larger per unit margins. With a larger margin to play with, there's more money available to spend on materials and workmanship quality. No one can afford to put $800 worth of glass working labor into an achromat that sells for $600. A similar aperture apochromat that sells instead for $1700, could indeed - economically - receive $800 in materials and workmanship investment.

As a result, apochromats today tend to be better quality than like aperture achromats.

Quality is king. Optical quality helps you beat the seeing. Helps reveal fine detail. It's well established that the difference between a 1/8 wave optic and 1/4 wave optic is quite detectable visually at the eyepiece.



- Jim


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PeterR280
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Re: Apochromatic or Achromatic does it really matter? new [Re: jrbarnett]
      #6079006 - 09/13/13 04:07 PM

From what I am reading, FPL-53 glass raw material cost could be over $400 for a 4" blank.

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Bonco
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Re: Apochromatic or Achromatic does it really matter? new [Re: ken svp120]
      #6079053 - 09/13/13 04:37 PM Attachment (23 downloads)

Quote:

I'm going to add my two cents by saying that a long achro might well be corrected as well as an apo but that the nice compact package of a modern apo makes such scope truly portable...you can take it to whatever dark skies you wish with very little transport worries and get phenomenal optical performance. Or, if permanently mounted, you can put it in a smaller facility. Yes, an apchromat definitely matters for more than one reason. Can you attain the same performance from an achromat...probably...but with the same functionality? I don't think so.




Here's a picture that illustrates your point. Televue 4 inch f/5 next to Antares 4 inch f/15. Both great telescopes and offer the best of both worlds. Wide field views in the f/5 are stunning. High power double star views in the f/15 are amazing. Take your pick, or buy both. Bill


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Kunama
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Reged: 10/22/12

Re: Apochromatic or Achromatic does it really matter? new [Re: Bonco]
      #6079102 - 09/13/13 05:12 PM

Very nice comparison Bonco !
Here is my version:
Istar Perseus AT150mm F10 on c1865 Gaunt Mount versus Takahashi TSA120 F7.5 on Vixen GPDII



oh by the way Jim, I think you got the info the wrong way around:

"Instead, because apochromats (fairly or not) are in higher demand. This means that manufacturers and dealers of such designs enjoy much larger per unit margins. With a larger margin to play with, there's more money available to spend on materials and workmanship quality."

I think the demand was a result of the high quality, not the cause of it !

In all seriousness, when it comes to visual on nebulae and other faint objects, APERTURE RULES !!! Go for an Istar Perseus AT150, one of the nicest modern achromats I have seen.


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Mark Costello
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Re: Apochromatic or Achromatic does it really matter? new [Re: jrbarnett]
      #6079110 - 09/13/13 05:28 PM

Based on what I seen it can do, I'm of the opinion that my achromat can perform to its design limits as well as any aprochromat can perform to its design limit. This may be true of a lot of achromats out there.

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VNA
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Re: Apochromatic or Achromatic does it really matter? new [Re: Mark Costello]
      #6079116 - 09/13/13 05:36 PM

Apochromatic or Achromatic does it really matter?

Yes it matters a great deal in the pocket book!

No one has really answered it other than proclaiming virtues of one or the other!

Is it worth 10 times more than an achromatic?

Is the view 10 times better?

(Law of diminishing returns)


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PeterR280
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Re: Apochromatic or Achromatic does it really matter? new [Re: VNA]
      #6079125 - 09/13/13 05:42 PM

The same can be said about size. Looka at the price differential between 100, 130, 150 and 175 mm. The resolution improvement is linear. Light gatherin does increase with the square of aperture. Cost seems to be logarithmic.

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Jon Isaacs
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Re: Apochromatic or Achromatic does it really matter? new [Re: VNA]
      #6079135 - 09/13/13 05:47 PM

Quote:

Apochromatic or Achromatic does it really matter?

Yes it matters a great deal in the pocket book!

No one has really answered it other than proclaiming virtues of one or the other!

Is it worth 10 times more than an achromatic?

Is the view 10 times better?

(Law of diminishing returns)




Your eyes are free. There is not telescope that can be justified in terms of how much better the view is. If one is looking for performance per dollar, a mirror is the way to go...

Jon


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Kunama
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Re: Apochromatic or Achromatic does it really matter? new [Re: VNA]
      #6079184 - 09/13/13 06:20 PM

Quote:

Apochromatic or Achromatic does it really matter?
Yes it matters a great deal in the pocket book!
No one has really answered it other than proclaiming virtues of one or the other!
Is it worth 10 times more than an achromatic?
Is the view 10 times better?
(Law of diminishing returns)




Of course the view is not 10x better, in fact on some targets there is almost no difference in the view, but then you point the scope at a bright cluster, Saturn, Jupiter or the Moon and you see the difference.

If the difference is worth the extra $$$ depends on the individual.

Like anything else, to get a small improvement in performance you have to spend quite a bit more.


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jrbarnett
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Re: Apochromatic or Achromatic does it really matter? new [Re: PeterR280]
      #6079609 - 09/13/13 11:25 PM

I doubt it given that Synta was selling complete 4" FPL-53 doublets for $450 under several different brands (Sky Watcher and Celestron). Of course, Ohara blanks come in different quality levels too, at widely varied costs.

Regards,

Jim


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Mike Clemens
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Re: Apochromatic or Achromatic does it really matter? new [Re: jrbarnett]
      #6079769 - 09/14/13 03:10 AM

When I first started, I owned a 6" achromat and then picked up a 4" APO. I almost never looked through the achromat again. The APO view was so insanely aesthetic in comparison.

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Maurice
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Re: Apochromatic or Achromatic does it really matter? new [Re: Jon_Doh]
      #6079811 - 09/14/13 04:40 AM

Thanks again for all the help gentlemen, this forum is really great!
Thanks to all your input I will be able to make a better choice.

To answer some of your questions: my current setup is a 80mm WO Zenithstar II ED mounted on a Voyager alt/az. I'm not into AP, but I do sketch the objects that I'm looking at, hence my wish for an alt/az with tracking ability. This little scope performs beautifully on the moon and star clusters, especially in combination with my UWAN16 eyepiece.

This shorttube however is not that useful on planets and nabulae due to the small aperture and short focal length. That's why I'm looking for a second scope, not to replace the shorttube but as an addition to it.

All your input makes me wondering, is the best addition to the shorttube not simply a "slow" refractor with an larger objective? So instead of the 152/900mm it looks to me I'm better off with for instance a 130/1200mm scope. The larger focal length also helps in reducing CA.

As an example my 80mm next to this one: http://www.teleskop-express.de/shop/product_info.php/info/p680_ELITE-127-Refr...

Makes sense or is the 120/900 ED a better option (regardless the price)?


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gdd
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Loc: N Seattle suburb, WA
Re: Apochromatic or Achromatic does it really matter? new [Re: Maurice]
      #6080061 - 09/14/13 09:47 AM

Quote:

All your input makes me wondering, is the best addition to the shorttube not simply a "slow" refractor with an larger objective? So instead of the 152/900mm it looks to me I'm better off with for instance a 130/1200mm scope. The larger focal length also helps in reducing CA.





Adding an AP CCDT67 reducer would convert the 130/1200mm to a 130/800mm.

Gale


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Jon_Doh
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Re: Apochromatic or Achromatic does it really matter? new [Re: gdd]
      #6080133 - 09/14/13 10:32 AM

There have been some folks who have tested an AR152 against the smaller aperture 127ED and reported that the smaller scope put up better views even on dimmer deep space subjects. I suspect this is due to the superior optics and the way the light is focused. This is something Jim may know about and can comment on.

I'm Just a former dumb football player and all this physics stuff goes over my head. But give me a receiver coming out of a crossing pattern on a single four wideout spread and I'll stuff him


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Mike4242
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Re: Apochromatic or Achromatic does it really matter? new [Re: Jon_Doh]
      #6080160 - 09/14/13 10:51 AM

I think this might be the review you had in mind:

http://www.cloudynights.com/ubbthreads/showflat.php/Number/5369924


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Jon_Doh
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Re: Apochromatic or Achromatic does it really matter? new [Re: Mike4242]
      #6080334 - 09/14/13 12:43 PM

Yes that is the review. DrWho posted it on another forum too. What is your take on this Mike? Have you had a chance to compare the achro with an apo? I'm wondering after your post about the difference the filter made on M13 whether the views between the 127ED and AR152 might not be closer.

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Jon_Doh
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Re: Apochromatic or Achromatic does it really matter? *DELETED* new [Re: Mike4242]
      #6080336 - 09/14/13 12:43 PM

Post deleted by Jon_Doh

Duplicate

Edited by Jon_Doh (09/14/13 02:21 PM)


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Mike4242
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Re: Apochromatic or Achromatic does it really matter? new [Re: Jon_Doh]
      #6080358 - 09/14/13 01:00 PM

I've done a few comparisons with a 120mm Eon, but not enough to really draw a conclusive opinion. I'm very interested in this right now because I'm trying to decide between buying a an Atlas Pro mount for the AR152 or a 120 ED and an Advanced VX. I'm really more interested in the lighter weight than the color correction, but if the color correction can make the 120 ED just as good as the AR152 on deep sky objects, then the move to the 120 ED would be worth the weight savings. However, if I'm losing deep sky performance by going to the smaller aperture, then I would rather get the mount. I had a C9.25 in the running for a couple of days, but decided against it because all of my eyepieces and accessories are more suited for a refractor.

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REC
Post Laureate
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Reged: 10/20/10

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Re: Apochromatic or Achromatic does it really matter? new [Re: Mike4242]
      #6080507 - 09/14/13 02:23 PM

Very nice and informative post and lots of threads.

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Jon_Doh
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Reged: 09/16/11

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Re: Apochromatic or Achromatic does it really matter? new [Re: Mike4242]
      #6080514 - 09/14/13 02:27 PM

Have you considered the 127ED? A true 5 inch triplet that supposedly does well on deep space according to some reviews. Right now I have the AR152 mounted on an AVX and it handles the big scope just fine.

I'm where you are right now trying to decide if the extra aperture is worth the bigger size and weight. And if a smaller ED/APO would do just as well on DSO's I would go that route in a minute. DrWho compared the two scopes under light polluted skies. I would like to see what the achro does with a filter since that supposedly corrects some of the noise caused by misfocusing the light.


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Mike4242
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Reged: 11/02/11

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Re: Apochromatic or Achromatic does it really matter? new [Re: Jon_Doh]
      #6080533 - 09/14/13 02:36 PM

I have considered the ES 127ED and might actually end up going that route. It seems that it can hard to catch the 127 essential edition in stock anywhere and to me carbon fiber is not worth an extra $1000. I'll probably be pulling the trigger on either the scope or the mount within the next few weeks.

I do hate the thought of spending $1600 on a scope and it be a step back from what I already have. Comments like the last 2 sentences from Neil English's article here really cause me to have some doubts. And Neil has looked through a lot of refractors both apo and achro:

http://neilenglish.net/further-adventures-with-filters/


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Jon_Doh
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Reged: 09/16/11

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Re: Apochromatic or Achromatic does it really matter? new [Re: Mike4242]
      #6080626 - 09/14/13 03:44 PM

The 127 Essentials no longer include a finder or diagonal. And Celestron mounts require a finder for alignment. So getting a 127 would cost closer to two grand. That's a big price difference for a little lighter and smaller scope. Maybe the answer is putting the right filter(s) on the achro and improving the views it gives.

Here are a couple more reviews about the achro that you may find interesting:
http://astroranch.wordpress.com/2013/02/25/explore-scientific-ar-152-achromat...
http://stargazerslounge.com/blog/1221/entry-1264-celestron-925-v-explore-scie...

And this one from our own Galaxyman who compared the AR152 with a six inch APO.

http://www.cloudynights.com/item.php?item_id=2051

The reviews do look favorable. I've found the CA to be very, very minimal and it doesn't bother me at all. In fact on the moon last night using a 6.7 ES 82 deg eyepiece I saw absolutely no CA in any of the craters. It was so minimal on the rim that when I shifted my head slightly it disappeared.

What did bother me was the ugly washed out, muddy view of M13 at medium magnification. But you indicated adding a filter really sharpened up the cluster and resolved the stars, correct? I know a lot of folks screw the Fringe filter onto their diagonal and leave it there all the time for the reason that it sharpens up stars.


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Mike4242
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Reged: 11/02/11

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Re: Apochromatic or Achromatic does it really matter? new [Re: Jon_Doh]
      #6080692 - 09/14/13 04:14 PM

Thanks for the links. Like you, the CA never really bothered me much, but after reading so many posts on the forum about smaller ED scopes performing just as well or better than larger achros, it makes you kind of curious. But I think you may be right -- it's not worth spending 2K just to find out. I'll most likely end up with a new mount.

BTW, I've noticed the same thing on the moon with ES 82 eyepieces. If you position your eye just right the CA seems to disappear.


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Jon_Doh
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Reged: 09/16/11

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Re: Apochromatic or Achromatic does it really matter? new [Re: Mike4242]
      #6080724 - 09/14/13 04:35 PM

I had read about people looking into the moon's craters and seeing green and purple halos because of the CA. That's why I wanted to crank up the magnification and when I did all I saw was more detail. In fact I even set up my 8 inch SCT with ACF optics nearby and looked at the moon with the same magnification to compare the view and thought the views looked the same. I had read that the CA was supposed to rob you of detail and contrast on the lunar surface but I did not find that to be the case at all.

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Maurice
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Re: Apochromatic or Achromatic does it really matter? new [Re: Jon_Doh]
      #6081513 - 09/15/13 04:43 AM

Quote:

What did bother me was the ugly washed out, muddy view of M13 at medium magnification. But you indicated adding a filter really sharpened up the cluster and resolved the stars, correct? I know a lot of folks screw the Fringe filter onto their diagonal and leave it there all the time for the reason that it sharpens up stars.





This is exactly what holds me back buying an achromat. I don't have the opportunity to look through a decent achro with Fringe filter so all I can do is read about it.
But M13 as an example; it looks beautiful in my 80mm ED, and resolves a lot of stars. All stars are shown as pin points. Will the view in a larger achro be an improvement at all?

Edited by Maurice (09/15/13 08:06 AM)


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beanerds
sage


Reged: 07/15/08

Loc: Darwin Australia
Re: Apochromatic or Achromatic does it really matter? new [Re: Maurice]
      #6081545 - 09/15/13 05:27 AM Attachment (14 downloads)

John Doh has obviously looked thru an Achro of the quality of my Istar 127mm f8 achromat ! , I don't see any 'Muddy ???'in mine either , even at 230x ( someone's word mate ) ?? , this is the sort of comment that make people like you Maurice think more than twice about, that's it's OK spending an obscene amount of money on an APO , when a good Achro will show the same ,,, it hurts me to see this , again and again here in these so called 'Refractor forums ' here in CN's ,, shame on you ! .
This is not 'APO' forums , if I am not mistaken ?.
Todays Achromats are top quality scopes and it really bugs me ( can you tell ? ) that some people bash them all the time ( un-educated ? , over ed-ucated ? ), because of a little CA , man I have seen CA in AP and Tak scopes at certain times over the years .
Brian.
ps. .
Its you money old mate and here is my home made 127mm Istar at the total cost of $1100 including mount , hope this helps ..

Edited by beanerds (09/15/13 05:45 AM)


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Maurice
member


Reged: 04/19/07

Loc: Netherlands
Re: Apochromatic or Achromatic does it really matter? new [Re: beanerds]
      #6081632 - 09/15/13 07:47 AM

Quote:

Its you money old mate and here is my home made 127mm Istar at the total cost of $1100 including mount , hope this helps ..




That is a beautiful scope for sure Brian!

Edited by Maurice (09/15/13 08:07 AM)


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Rutilus
Carpal Tunnel


Reged: 12/17/10

Re: Apochromatic or Achromatic does it really matter? new [Re: beanerds]
      #6081643 - 09/15/13 08:00 AM Attachment (13 downloads)

Yes- you don't have to spend vast amounts of money to get excellent eyepiece views. I picked-up a Carton 4" f/13 lens for a very good price
and built a tube around it.The total cost was less than my Tak 7x50 finder and bracket that I had on my TSA-102.

In tests along side my Tak and an FS-102, the Carton showed the same planetary and lunar detail. All three scopes went
about it in a different way, i.e. the TSA very clinical in its approach to objects, while the FS had a slighlty warmer tone.
The Carton, being an Achro shows some C.A., but the same detail is all there.
I sold the TSA to raise funds for other projects, one being an Istar 6" f/15 lens.
Here is a pic of the Carton, while the tube is longer than the Tak, I actually find the Carton easier to mount
than the now gone TSA. While only 4" the triplet lens in the Tak was quite nose heavy.

Edited by Rutilus (09/15/13 08:03 AM)


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Jon_Doh
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Reged: 09/16/11

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Re: Apochromatic or Achromatic does it really matter? new [Re: Rutilus]
      #6081763 - 09/15/13 09:55 AM

Regarding CA, I see much less CA on the moon with the 152 than I do with an SCT with high end optics. The CA in the 152 is hardly noticeable and disappears when I move my head slightly. The CA through the SCT is a distinct, defined yellow band around the moon. I see no CA through the SCT on bright stars, Jupiter or Venus - just the moon. Haven't seen any CA on stars with the 152 yet and haven't had a chance to look at Jupiter and Venus which may be a game changer.

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PowellAstro
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Reged: 10/14/09

Loc: Tennessee
Re: Apochromatic or Achromatic does it really matter? new [Re: Jon_Doh]
      #6081791 - 09/15/13 10:16 AM

I have the AR152 which I re-spaced the objective for SA and CA. It resolves tighter and brighter stars on m13 than my very good 8" SCT and much better than a 100mm ED refractor. It also out performs the 120mm ED that I have tested with it many times. Against the 120, the difference is not huge but the 152 is a little better.

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Jon_Doh
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Reged: 09/16/11

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Re: Apochromatic or Achromatic does it really matter? new [Re: PowellAstro]
      #6081807 - 09/15/13 10:27 AM

You could start a little side business upgrading 152's!

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Mike4242
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Reged: 11/02/11

Loc: Memphis, TN
Re: Apochromatic or Achromatic does it really matter? new [Re: Jon_Doh]
      #6082493 - 09/15/13 05:37 PM

Quote:

It also out performs the 120mm ED that I have tested with it many times. Against the 120, the difference is not huge but the 152 is a little better.




Thanks! Exactly what I was looking for.


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Fomalhaut
scholastic sledgehammer


Reged: 08/16/08

Loc: Switzerland
Re: Apochromatic or Achromatic does it really matter? new [Re: Mike4242]
      #6082593 - 09/15/13 06:35 PM

After having reached the end of the column there always seems to rise the same question: How to decrement and skip back on zero??!!

Such as:
-After having sold many 100 to 120 deg eyepieces => let's go back to selling "new" orthos!
-After having sold EDs and even APOs to everyone who could afford => let's celebrate the ordinary achromat as a further advancement and firmly hope there will be many believers! $$$

(=> Other examples certain to follow... This process is called marketing.)

Obvious goal: to dodge saturation of the market.

I'm not speaking of cheep(ly produced) Chinese ED-"Apos", but a real top-notch 4- to 6-inch APO will make any f/12 to f/15 Achro of comparable aperture eat nothing but dust, as sure as I have owned and used top examples of both kinds

Chris


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timps
sage


Reged: 02/24/13

Re: Apochromatic or Achromatic does it really matter? new [Re: Fomalhaut]
      #6082892 - 09/15/13 09:58 PM

I have had my Chinese made "Konus" 120mm Achro for 14 years now. I was considering a Tak TOA130 earlier in the year but after looking through one, found for the extra $5000, the difference visually was not worth it. For imaging though its a different story. CA in my Konus is only noticeable at higher magnifications. I achieve the sharpest and most detailed planetary views with my Televue 11mm Plossl. Just after I purchased it, I was able to use it along side a Meade 10" SCT in dark skies and the little Konus 4.7" always gave more detailed and sharper views of Jupiter and Saturn.

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