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Achro Vs Apo

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#1 timps

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Posted 22 March 2013 - 03:14 AM

I was wondering if a large aperture long focus achro would give just as detailed planetary images as a smaller aperture apo. I had my first look through an apo the other night (tak TOA130). Yes the image was sharp, CA free and brighter than my 120mm Chinese achro, but the view didn't "blow me away" as I was expecting. The Tak obviously showed a little more detail and didn't require as much affort to see it but is that worth the $5,500 extra?
Could I match the detail shown in the TOA130 with a 152mm f12 - f15 Achro or maybe an 8" achro like Istar produce?

#2 orion69

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Posted 22 March 2013 - 03:29 AM

I'm only guessing here, but I would say that 8" Istar f12-f15 would visually blow away TOA130 for planetary (or any other 130mm APO).

#3 Jon Isaacs

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Posted 22 March 2013 - 03:48 AM

I'm only guessing here, but I would say that 8" Istar f12-f15 would visually blow away TOA130 for planetary (or any other 130mm APO).


What would "blow you away" is the scope that was somewhere between 8 and 10 feet long, the mount required to handle the scope and the wide range of eyepieces heights, and it would still only be an 8 inch scope.

Jon

#4 bherv

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Posted 22 March 2013 - 04:28 AM

A 12" f/5 Dob will show you more than any of those scopes and at a lower price.
Barry

#5 beanerds

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Posted 22 March 2013 - 06:40 AM

Good 'Q' Timps , all I can say is , is my 63mm f11.4 Zeiss telementor has worse CA than my 60mm f5.9 Takahashi FS60C .
so thats f11.4 vrs f5.9 .

840mm Zeiss achromat and 355mm Takahashi Fluorite .
Apo Vrs. ACHRO .

Personally I like the more natural colours of the moon and planets thru the Zeiss , more CA for sure .

The Tak FS60C APO is better , brighter views , smaller Aeire discs , easier to use , bla ,,,
But ...
The TakahashiFS60C is so good on everything , but she starts looking ,,, clinical ? where the Achro of the Zeiss is more natural , it aint just me seeing this .

Long throw Achromats for luna, planetary views are better .

Not an easy call , Achro's are more natural .
Brian.

#6 Jon Isaacs

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Posted 22 March 2013 - 06:51 AM

Not an easy call , Achro's are more natural .


In terms of rendering the spectrum of colors "naturally", accurately, Newtonians are the standard. In my admittedly limited experience, apo's are closer than achromats to the natural, accurate rendering of the Newtonian. If you like a little tint, there are a number of filters available. :ubetcha:

Jon

#7 Jim Curry

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Posted 22 March 2013 - 07:32 AM

A 6" f/12 or f/15 Istar may not "blow away" the 130 but it will provide a far more satisfactory view which can only be appreciated after an evenings use. There is always the bogeyman of secondary color as an argument against the achro but do not be afraid. And no, I haven't looked through a 130. Aperture and a smooth polish to the achro will result in higher resolution. An 8" f/12 will be a complete hawg wrastle for portability.

The detractors of these long f ratio achros have short memories. Achros participated in pushing back the frontiers of astronomical science up to and including the present times. What have apo's contributed? :gramps:

Jim

#8 orion69

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Posted 22 March 2013 - 07:46 AM

Not an easy call , Achro's are more natural .


You are kidding, right? ;)

#9 t.r.

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Posted 22 March 2013 - 07:54 AM

Here is what I was told by Barry Greiner of D&G Optical (a top US achromat manufacturer)which I think is a good rule of thumb and latter confirmed by my own field experiences...an achromat that is one inch larger than an apochromat will show as much planetary detail as the smaller BUT with chromatic aberration (CA,the purple blur) that may be bothersome to some people. This applies up to about 8 inches of aperture, where finally the CA becomes problematic in reasonable focal lengths. Filters reduce this CA to a level some can live with. Barry told me before the advent of the special "minus violet" filters, the filter choice was a simple color filter No.8 Light Yellow. I have one of these for my 80mm F/5 and it does indeed improve the view for high power planetary viewing adding another 50x that I can use productively.

What folks really get for their money when getting an apo is a very short, portable and fully corrected optic that can be used for better imaging and wonderful visual. A visual only user may indeed be completely happy with an achromat of short or long focus, simply depending on how much the chromatic aberration bothers them on a personal level that really can only be determined through experience! All the charts, reports and testimonials aren't going to be able to tell you if an achromat will work for you...ONLY YOUR EYES will determine that. If you weren't "blown away" by the TOA130 view compared to the chinese 120...it should tell you something! ;) However, don't expect the same response from someone else looking through the same two scope you did! :bow:

#10 SteveSMS

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Posted 22 March 2013 - 08:02 AM

I don't mean this to be offensive, but have you considered the size, weight, and cost of a mount capable of supporting a long focus 6" or 8" refractor? You owe it to yourself to find someone with a 8" or larger dob that is thermally managed and collimated that is willing to point it at Jupiter for you. My guess is that you will be "blown away."

#11 Mark Costello

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Posted 22 March 2013 - 08:17 AM

I'm only guessing here, but I would say that 8" Istar f12-f15 would visually blow away TOA130 for planetary (or any other 130mm APO).


What would "blow you away" is the scope that was somewhere between 8 and 10 feet long, the mount required to handle the scope and the wide range of eyepieces heights, and it would still only be an 8 inch scope.

Jon



I believe myself to be a refracto-fanatic but lookiing at these larger refractors like an 8" make me feel like :crutch: :crutch:. My 5" achro sets up easily enough but is about as large as I'd want a refractor to be. Any larger scope I get will work mostly or completely with mirrors. :lol:

#12 Jim Curry

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Posted 22 March 2013 - 08:19 AM

I use my 6" f/12 on a G11 with extension. It's fine for visual but I consider it at its limit. Adding another 18" to that OTA? I dunno...

Jim

#13 hottr6

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Posted 22 March 2013 - 08:50 AM

...have you considered the size, weight, and cost of a mount capable of supporting a long focus 6" or 8" refractor?

Anyone who has the funding to consider a TOA130 or an 8" achro will most likely have the funds for an appropriate mount, and if space is available, a small observatory. I don't see anyone that deep into the hobby who would consider an OTA as the only component of a system.

Otherwise, the question is purely rhetorical.

#14 dan_h

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Posted 22 March 2013 - 09:01 AM

The detractors of these long f ratio achros have short memories. Achros participated in pushing back the frontiers of astronomical science up to and including the present times. What have apo's contributed? :gramps:

Jim


Perhaps a good question to ponder but not a valid argument to assert the value of an achro over an apo.

Look what Columbus did with a small sailing ship. And almost all of the great railroads of the world were opened under steam locomotives. The heyday of radio came with the invention of the vacuum tube and televison was founded on old monochrome CRTs. There are many, many, many technolgies that have had their day and have now been relegated to the museums. The fact that these technologies were once the greatest tools available, doesn't make them the best today.

dan

#15 SteveSMS

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Posted 22 March 2013 - 09:10 AM

Astronomy is not the only hobby that people don't have the "FULL" funding to enjoy. I don't doubt for one minute that there are OTAs out there that can't be used due to the owner not being able to afford a proper mount. It's the same as hobbies like boats or cars where folks bite off way more than they can actually chew and things just sit around unused or get sold for a loss.

#16 orion69

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Posted 22 March 2013 - 09:49 AM

OP question was not how heavy or large 8" achro refractor is, or what mount should one buy to support it.

Btw, I own 152mm achro and it's too big and too heavy for me and that's one reason I used it only few times (other is CA).

#17 watcher

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Posted 22 March 2013 - 09:54 AM

Why is it that any time someone mouths the words "long focus refractor", the conversation degrades to the size and mount requirements, and why Dobs are a better choice,because their far less expensive, and why APO's are so superior because they're so much more expensive? I am just as happy with a long achro's views. There might be a minor discrepancy that allows a bit more to be seen with an APO of slightly smaller aperture, but well figured optics always delight. Whether it's a 60 or 100mm Carton, or a 6 or 8" D&G, Most will be happy with what a long achro can do in comparison to the similar aperture of ANY other type of scope. Want to talk about mounting issues or bang for the buck of aperture, let's do a thread about that if someone is asking about a decision to purchase, not for a discussion about performance.

#18 ValeryD

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Posted 22 March 2013 - 10:54 AM

Here is what I was told by Barry Greiner of D&G Optical (a top US achromat manufacturer)which I think is a good rule of thumb and latter confirmed by my own field experiences...an achromat that is one inch larger than an apochromat will show as much planetary detail as the smaller BUT with chromatic aberration (CA,the purple blur) that may be bothersome to some people.


This may be true for 2" apo v 3" achro, for 3" and 4". But sure not for 6" and 7" and more so not for 7" vs 8".

My 5" excellent APO consistently showed more delicate details on Jupiter than 150mm F/10 achromat (ideally made, collimator from the test bench).


Valery.

#19 Jim Curry

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Posted 22 March 2013 - 10:54 AM

Ahh Dan,

You didn't address my question. I never suggested an achro is THE cutting edge of anything only that they still contribute to science and my question suggests that apo's don't. Correct me if I'm wrong, but apo's are instruments solely in the hands of amatuer astronomers for visual and photo hobby (play)endevours. It was just a few years ago, 1980ish, that an antique 9" f/13 achro (deep in the allegedly no-no wasteland of purple haze ;)) was used to DISCOVER the rotation of Uranus wihin a percent or two as well as DISCOVER the phenomena of spokes in Saturns rings. To roughly quote O'Meara, "there was always a lot of blue around the images, but the resolution was incredibly sharp and contrast was very good." It only took a several billion dollar program to visit the scenes and confirm.

Clear skies,
Jim
(all in good fun)

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#20 JKoelman

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Posted 22 March 2013 - 12:04 PM

I never suggested an achro is THE cutting edge of anything only that they still contribute to science and my question suggests that apo's don't.


Exoplanet hunter KELT-North sports a 71mm f/2.8 APO.

#21 Eddgie

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Posted 22 March 2013 - 12:16 PM

Could I match the detail shown in the TOA130 with a 152mm f12 - f15 Achro or maybe an 8" achro like Istar produce?



You were not blown away by a 5" APO? Then a 6" achromat is not going to blow you away either.

In fact, it is unlikely that even a 6" APO will "blow you away." The step up is subtle, even if it is to a 6" APO.

While not a Tak, I have owned 4", 5", and 6" APOs.

None of them would be my first choice for serious planetary observing.

Consider a 10" f/6 reflector with premium mirrors, Even this might not blow you away, but it will give a very meaningful improvement over where you are now.

Until refractors get rather large (8") it is hard to match the view you can get from a 10" or 12" reflector with high quality mirrors.

If better planetary views are what you seek and want to see a meaningful improvement, you won't get it with 6" f/15 achromat.

Go a lot bigger, or go home.

#22 TG

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Posted 22 March 2013 - 01:12 PM

One thing that almost never gets mentioned for planetary observing is a tracking mount. Being able to relax and take in the details is essential to capturing those "blown away" moments. I've used a very smooth dob but tracking is a chore and limits you to about 250x. Now some people claim to track manually at powers far higher than that but not being most people I sometimes wish I could put my 6" Mak-Newt back on an EQ mount.

For this reason, I'd rather go with a large SCT (say a C9.25/C11/C14) which my mount can handle rather than a large newt which it can't and which would need a dedicated and probably pricey tracking platform.

Tanveer.

#23 Jim Curry

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Posted 22 March 2013 - 02:07 PM

Bingo! I'm not surprised someone would correct me.

Thanks, Johannes

#24 Levine

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Posted 22 March 2013 - 02:55 PM

Hmmm...

One of my favorite instruments is my Cotosky 210mm f/6 Fraunhofer doublet.
It is "only" 48" long, but light enough to readily transport and mount. Better for deep-sky scanning, but when coupled with a minus-violet filter for the four objects in the known universe that will throw up some serious CA, the planetary images are not awful.
The FS-128 may be sharper overall, but the additional 3" of aperture offered by the Achro, in addition to the resulting brighter, larger image, provides some decent detail, too.

#25 Tank

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Posted 22 March 2013 - 03:25 PM

I would take a smaller APO anyday over a larger Achro.
CA becomes intrusive and degrades the image in great seeing.
One reason that the 130 TOA didnt blow you away was most likely seeing conditions!!!
Actually to tell you the truth if the seeing conditions were bad the larger scope would even make the view more unpleasant and washed out!
Seeing conditions are most misunderstood you can have a AP178 and a 80APO in really poor seeing the smaller scope the image will be more pleasing!
Bottom line APOs are great instuments and i honestly say you cant compare a APO to a ACHRO!






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