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Are Achros Sharp Planetary Scopes

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#26 SeattleScott

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Posted 02 March 2020 - 01:17 AM

The Moon isn’t bad for CA in a 4” F10, as long as it isn’t too full. Neither is Saturn or Mars. Jupiter is the only one that struggles a bit in a slow achro.

F7 is a different story.

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#27 Hesiod

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Posted 02 March 2020 - 06:48 AM

If have a well crafted objective, smooth, rightly spaced and well corrected for SA, can do nice planetary observations especially through colored filters.
My guess is that chances are higher if opt for a mid/slow model (my tal 100/1000 is rather nice)

#28 25585

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Posted 02 March 2020 - 07:14 AM

They can be quite good if they are slow. My A105M does very well on planets. I suppose it should for the price. Seems to me it would be rather pointless to make a high end fast achro so you don’t really see those, other than the recently discontinued NA140.

I also have owned an AR102. Nice scope but too fast to do well on planets.

Scott

I looking forward to trying my A102M on planets.

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#29 Sarkikos

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Posted 02 March 2020 - 07:17 AM

Are Achros Sharp Planetary Scopes?

 

Only if they are very slow.  Or you don't mind putting in a filter that makes the image yellow.

 

Mike


Edited by Sarkikos, 02 March 2020 - 07:20 AM.

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#30 MalVeauX

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Posted 02 March 2020 - 08:23 AM

Heya,

 

Well, I wouldn't call them sharp planetary scopes, since sharpness is a function of contrast and an achromatic doublet with even a little chromatic aberration will lack some contrast in an area where some wavelengths are not at focus.

 

That said, I still often enjoy viewing planets with my arhcomatic doublets; I have several. I generally use this 120mm F10 masked doublet (150mm F8 without the mask) and it handles things quite well and is incredibly convenient to view through. I usually try and use my 127mm Mak from the porch or my 200mm F6 Quartz Newt for planets. But sometimes I just like to look with the 120mm F10 and a pair of binos. Good contrast, fairly sharp, some CA.

 

I don't bother with filters, the filters do not correct focus of the light, the filters merely mask the CA color, so I'm not sure why anyone uses filters for viewing in the presence of CA other than somehow it helps them be at ease not seeing the purple-green fringe, even though its still there, just with a yellow hue to it with a filter.....

bombdrop.gif

 

(120mm F10.... that's an ED80 on its back for size reference)

 

Solarsetup_02232020.jpg

 

Very best,


Edited by MalVeauX, 02 March 2020 - 08:24 AM.

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#31 Jon Isaacs

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Posted 02 March 2020 - 08:40 AM

Heya,

 

Well, I wouldn't call them sharp planetary scopes, since sharpness is a function of contrast and an achromatic doublet with even a little chromatic aberration will lack some contrast in an area where some wavelengths are not at focus.

 

That said, I still often enjoy viewing planets with my arhcomatic doublets; I have several. I generally use this 120mm F10 masked doublet (150mm F8 without the mask) and it handles things quite well and is incredibly convenient to view through. I usually try and use my 127mm Mak from the porch or my 200mm F6 Quartz Newt for planets. But sometimes I just like to look with the 120mm F10 and a pair of binos. Good contrast, fairly sharp, some CA.

 

I don't bother with filters, the filters do not correct focus of the light, the filters merely mask the CA color, so I'm not sure why anyone uses filters for viewing in the presence of CA other than somehow it helps them be at ease not seeing the purple-green fringe, even though its still there, just with a yellow hue to it with a filter.....

bombdrop.gif

 

(120mm F10.... that's an ED80 on its back for size reference)

 

 

 

Filters eliminate a certain amount of out of focus light, leaving a more focused image.

 

In this context, standard Wratten type planetary filters make more sense than a filter that tries to turn an achromat into an apo. Using a number 25 on Mars can be useful in an apo or Newt, it would be even more so in an achromart because the narrower band would be more tightly focused. 

 

Jon


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#32 GOLGO13

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Posted 02 March 2020 - 09:03 AM

I think it has to be at least F10 for an achromat (say 4 inches and below). I did test this out a few years back. I picked up a nice 102mm F11. It was a wonderful scope surprisingly. Fit and finish was great!

 

However, my 103s was better in every way when directly comparing them. And thus I gave up that experiment. However, That scope was really cool. And certainly would be fine for someone who didn't want to spend the extra cash on an apo. But it was really long!

 

DSC 0137

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#33 Sarkikos

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Posted 02 March 2020 - 09:06 AM

Currently, I observe with achros for low-power, wide-field, deep sky only.   And they are fast achros.  I enjoy observing deep sky with my f/5 and f/4.5 achros.  Yes, they have field curvature.  But a field flattener will correct for this.  There is no good way to correct for CA. 

 

So I don't view anything with achros that would make the CA obvious.  Jupiter?  Forgetaboutit.  To obtain halfway decent CA correction, you need a very slow achro, which means more weight, length and cumbersomeness.  I'm done with that.  The only slow achro I have left is an old Towa 60 f/15, which I never use.  The AT60ED is much more compact for grab-n-go and has a wider range of available magnifications.

 

For double stars, planets and the Moon I use ED/APOs, Newts or Cats.  My best - sharpest, brightest image, widest color range, most detail seen - telescope for planet/lunar is my 10" f/4.8 Dob.

 

Mike


Edited by Sarkikos, 02 March 2020 - 09:22 AM.

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#34 bobhen

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Posted 02 March 2020 - 09:18 AM

Many years ago I was at my club’s public star party. I set up my Astro-Physics 152 F9 triplet next to a 4” F15 Edmunds refractor and a 6” F15 Jaegers refractor we were all observing Jupiter. Because it has some low contrast features, Jupiter is a good target to use to judge optical quality and performance.

 

The 4” F15 Edmunds put up a pretty nice view – I was impressed. The 6” F15 Jaegers showed more color than I liked but both achromats did a good job. However, there was no comparison with the view in the AP 152 F9. There was no color and an obviously sharper view that translated into fine line and popping micro detail.

 

Note that my 1989 AP 152 was a pre ED scope. Today’s "high quality" apo triplets can be shorter and better color-corrected and are superb high power lunar/planetary and imaging telescopes.

 

Bob


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#35 LDW47

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Posted 02 March 2020 - 09:44 AM

If you are going to be strictly a moon / planet observer a long tube is a great choice but if you are going to be more versatile, more broad in your viewing experiences you had better stick with 80-100-127mm something in the f6’s range ! Your eggs will spread out better in your basket, lol ! As to views with the shorter scopes, filters can remove a lot of the color problems ! Clear Skies in the future observations !


Edited by LDW47, 02 March 2020 - 11:08 AM.


#36 Sarkikos

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Posted 02 March 2020 - 10:45 AM

A little bit loose ended let’s stick to observation made by the better branded achros and without criticizing their color performs how do they do in terms of sharpness on planetary objects visually.

Well, we really do need to criticize their color performance because chromatic aberration can substantially degrade sharpness on planets during visual observation.

 

Mike



#37 mikeDnight

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Posted 02 March 2020 - 10:50 AM

My Vixen F13 was a wonderful scope on the planet's and even on deep sky. And one evening in 2001 I saw a home made 5" F11 uncoated achromat destroy a 6" F8 Chinese achro. At my local astro club we have an 8.5" achromat that nothing beats on the planet's, no matter what the aperture. So yes, a good achromat can definitely be a terrific planet scope, but I think their magic lies in their longer focal length.


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#38 Shorty Barlow

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Posted 02 March 2020 - 11:08 AM

Well, we really do need to criticize their color performance because chromatic aberration can substantially degrade sharpness on planets during visual observation.

 

Mike

This is the crux of the matter I believe. My relatively inexpensive and slightly modified ST102 is primarily designed for rich field observing and basically just a bigger ST80. 

 

sml_gallery_249298_10069_26682.jpg

 

I rarely use it above 30x and often lower than that. It's the biggest refractor I have that is relatively quick and easy to set up (I have a physical disability) on my AZ5. As a consequence it gets used a lot as a grab and go on Moonless nights. As Jupiter and Saturn make a comeback I can also take a peek at them with it. The only way I can get a half decent image is to use a Barlow (effectively slowing the focal ratio) combined with various minus cyan filters. I don't own a slow achromat. I find the CA noticeably kicks in around just above 60x. I've often looked at a rising Moon or planets with the ST102 and even with a Barlow the CA degrades the sharpness of the image. Admittedly the doublet isn't the highest quality to begin with, but it's the CA that degrades the image. 


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#39 t.r.

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Posted 02 March 2020 - 11:13 AM

Go down to Color Correction and Visual Impressions...(pay attention to the comparison to reflectors)…

http://bobmay.astron.../Refrdesign.htm

Refractors do have a contrast advantage...CA and all! That’s how they got their reputation in the first place...long focus filtered achromats can best the planetary image put up by reflectors. Fact!

Edited by t.r., 02 March 2020 - 11:17 AM.

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#40 GOLGO13

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Posted 02 March 2020 - 11:22 AM

Yesterday I was testing out my new 6 inch F5 on the Moon. It actually didn't do too bad with my 30mm Ultima. 

 

With the binoviewer and 16mm Brandons the CA was starting to show a bit.

 

I got out the 81s and wow...such a big difference. Of course the 6 inch F5 is not meant for that type of observing and that's not what I got it for.

 

The nice thing about Vixen's ED scopes are they are F7.7. So kind of a nice mix of portable and slightly longer focal length. They are great planetary scopes.


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#41 Sarkikos

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Posted 02 March 2020 - 11:30 AM

Go down to Color Correction and Visual Impressions...(pay attention to the comparison to reflectors)…

http://bobmay.astron.../Refrdesign.htm

Refractors do have a contrast advantage...CA and all! That’s how they got their reputation in the first place...long focus filtered achromats can best the planetary image put up by reflectors. Fact!

My experience with achromats showed a disadvantage for contrast.  I could see an obvious smearing of surface details for Jupiter through my 4" f/10 achromat.  I had two of them.  Smeary Jupiters through both.  I tried various VR and color filters.  Any filter which substantially reduced CA produced a yellow image, which reduced contrast for planets due to loss of color range.  And for double star observation, you lose color contrast between the stars.  A lose lose situation in both cases.

 

I wouldn't bother with even slower achros.  I'd just go for a more compact ED/APO, or even better, a Newt with larger aperture.

 

Mike


Edited by Sarkikos, 02 March 2020 - 11:33 AM.

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#42 Shorty Barlow

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Posted 02 March 2020 - 11:50 AM

Go down to Color Correction and Visual Impressions...(pay attention to the comparison to reflectors)…

http://bobmay.astron.../Refrdesign.htm

Refractors do have a contrast advantage...CA and all! That’s how they got their reputation in the first place...long focus filtered achromats can best the planetary image put up by reflectors. Fact!

Interesting link, thanks.



#43 Shorty Barlow

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Posted 02 March 2020 - 11:53 AM

My experience with achromats showed a disadvantage for contrast.  I could see an obvious smearing of surface details for Jupiter through my 4" f/10 achromat.  I had two of them.  Smeary Jupiters through both.  I tried various VR and color filters.  Any filter which substantially reduced CA produced a yellow image, which reduced contrast for planets due to loss of color range.  And for double star observation, you lose color contrast between the stars.  A lose lose situation in both cases.

 

I wouldn't bother with even slower achros.  I'd just go for a more compact ED/APO, or even better, a Newt with larger aperture.

 

Mike

I agree about double stars as well. It defeats the object to see them all with a yellow tint lol.


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#44 kmparsons

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Posted 02 March 2020 - 12:51 PM

My experience observing with 4" f/10 and f/12 achros is that they can give deeply satisfying views of the Moon and planets. I did not see any smearing or distortion. The views were razor-sharp. My much more expensive 4" triplet apo does outperform them, but not by what I would consider a large margin. Compared to my 3" triplet apo--also much more expensive than the 4" achros--the apo is color free, but the larger aperture of the achros more than compensates, IMO. The upshot, is that a well-made achro can give very satisfying planetary and lunar views for a price significantly less than a premium apo of smaller aperture. In balancing price vs. performance, therefore, you would do well to consider a long (or longish) achromat. 


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#45 shaesavage

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Posted 02 March 2020 - 01:03 PM

My Telementor II (f 13.3) and my Takahashi TS-65 (f 15.4) are outstanding considering their diminutive aperture. They never stop amazing me with the amount of detail you can see!

 

I used to own a Tasco 7TE-5 that blew my mind on Mars. Planetary detail doesn't slap you in the face the way it would in a 4" or 5" refractor....but it's there.


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#46 Sarkikos

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Posted 02 March 2020 - 01:21 PM

My experience observing with 4" f/10 and f/12 achros is that they can give deeply satisfying views of the Moon and planets. I did not see any smearing or distortion. The views were razor-sharp. My much more expensive 4" triplet apo does outperform them, but not by what I would consider a large margin. Compared to my 3" triplet apo--also much more expensive than the 4" achros--the apo is color free, but the larger aperture of the achros more than compensates, IMO. The upshot, is that a well-made achro can give very satisfying planetary and lunar views for a price significantly less than a premium apo of smaller aperture. In balancing price vs. performance, therefore, you would do well to consider a long (or longish) achromat. 

Not of Jupiter, in my experience.  Jupiter is the crucial test.

 

Mike



#47 k5apl

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Posted 02 March 2020 - 01:36 PM

Another $.02 for consideration.  I own a 130mm/f6 refractor, a 92mm/f6 refractor (both triplets) and a 102mm/f13

Achromatic doublet refractor.  Jupiter and star patterns have been compared by myself and other accomplished observers under very good skies.

 

The overwhelming comments when viewing through the Achro were "how sharp the image is" and "much less color than expected".  The "color" was the purple haze around Jupiter.  Their conclusion was that the old timers like

Walter Scott Houston didn't have it so bad after all.

 

I use the Triplets the majority of the time but will keep the Achro because it looks like a real telescope to many older

folks and newbies, and they can see that they can get a pretty darn good performer for less investment.    Its just

fun to use it and share it with others.

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#48 t.r.

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Posted 02 March 2020 - 01:40 PM

I have no problem with Jupiter in achros with a filter. There will be no new unseen planetary detail that suddenly pops into view in an apo or reflector of like size. The color hue imparted is only relevant to some, the critical detail/ resolution remains the same. But I digress...we have been round about it before...just please let others have their opinion and experience through...it doesn’t have to be countered.

#49 Sarkikos

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Posted 02 March 2020 - 01:45 PM

I have no problem with Jupiter in achros with a filter. There will be no new unseen planetary detail that suddenly pops into view in an apo or reflector of like size. The color hue imparted is only relevant to some, the critical detail/ resolution remains the same. But I digress...we have been round about it before...just please let others have their opinion and experience through...it doesn’t have to be countered.

scratchhead2.gif  

 

I will let others share their experience.  How am I going to stop them?  But that doesn't mean I'm not going to share mine!  grin.gif

 

I see more surface detail through my NP-101is than the 4" f/10 achros I used to own.  Unfair comparison?  No comparison is unfair.  Just the facts as I see them.

 

Mike


Edited by Sarkikos, 02 March 2020 - 01:46 PM.

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#50 Sketcher

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Posted 02 March 2020 - 01:58 PM

What can be seen in the way of planetary detail with an 80mm f/5 achromat (with a considerable amount of CA), without using any filters?

 

ST 80 Saturn   Sketcher
 
ST 80 Jupiter   Sketcher

 

Are those "sharp"?  Well, it kind of depends.  What do you want to compare the views to?  Are there smaller telescopes that can provide sharper views?  Yes, there are.  Does that matter?  --  Depends on who you talk to.

 

Can a person be happy with seeing that much (or that little) with an 80mm telescope?  Well, that's going to depend on the person.  Some are OK with that level of planetary detail.  Others are OK with it as long as they can also do plenty of other (than planetary) observing with the same telescope.  There are compromises no matter what telescope one is looking at.

 

OK, so let's look at a telescope that has a humongous amount of Chromatic Aberration (CA):  How about a 6-inch f/6.5 achromat?

 

Jupiter June 13 2018 AR152 200x Sketcher
 
Mars 6 inch F 6.5 achromatSketcher   text

 

Are those images sharp?  Well, they're better than what the 80mm f/5 achromat could show.  But once again, there are smaller (than 6-inch) telescopes that can provide sharper views.  On the other hand, there are also larger telescopes that can provide worse views!  There are no simple answers to the original question.

 

Even without using any filters, the 6-inch f/6.5 achromat can show Jupiter's Galilean satellites well enough to identify each individually by nothing more than their differing apparent diameters.  Or even by nothing more than their differing colors -- yes, by their colors -- yes, with a large, fast, achromat -- despite the huge amount of CA.  You see, CA has its impact on the visual image; but it doesn't impact all details in the same manner.

 

Yet, there are other telescopes, even smaller telescopes, that can do better -- much better on low-contrast details.  But on high-contrast details the larger achromat (even with its CA) will often come out on top.

 

I have a 5-inch apochromat that can show noticeably sharper (overall) planetary views than the 6-inch achromat mentioned above.  Does that make the 6-inch telescope "worthless" as a planetary telescope?  Well, that's going to depend on who you ask.  But my 5-inch apo cost about 4-times as much (in 1995 dollars) than the 6-inch did in (2015 perhaps?) dollars.  That's quite a price difference.

 

Do you buy a telescope to compare its performance with another telescope; or do you buy a telescope to see all that you can see with it?  These are important, even critical, questions.  How much planetary detail is enough?

 

Personally, I can be a happy observer using my achromat refractors -- even for planetary observation.  This, even when I have other telescopes that will show more.  But I'm probably not incorrect to say that most others don't share this perspective.

 

There are just so many things to take into consideration . . .

 

Confused enough yet?


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