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Are Achros Sharp Planetary Scopes

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#1 HCR32

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Posted 01 March 2020 - 08:13 PM

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.
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#2 Kunama

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Posted 01 March 2020 - 08:17 PM

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.

I'll tell you in a couple of months when the planets get with the plan......

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#3 coopman

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Posted 01 March 2020 - 08:20 PM

The problem is that the CA affects their ability to show fine planetary detail, so you can't dismiss it.
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#4 SeattleScott

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Posted 01 March 2020 - 08:21 PM

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

Edited by SeattleScott, 01 March 2020 - 08:22 PM.

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#5 coopman

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Posted 01 March 2020 - 08:29 PM

Also, the CA gets worse as you increase the magnification. 



#6 Shorty Barlow

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Posted 01 March 2020 - 08:39 PM

Yeah, the CA is the main limiting factor I reckon. 

 

med_gallery_249298_5346_82396.jpg

 

My ST102 isn't bad on the Moon, Jupiter and Saturn with a Baader Fringe Killer/Neodymium stack.


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#7 Tyson M

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Posted 01 March 2020 - 08:40 PM

I have been wondering this myself. 

 

I think I am going off the deep end in like 5 years and try to build an observatory with very large Istar 9.8" f11 R30 lens.  Order the lens sooner first just to make sure I got it, then build the observatory, source a tube and focuser, find a suitable mount ect.

 

I am hoping it to be my deep sky/planetary all-rounder. Maybe stop it down and/or use binoviewers


Edited by Tyson M, 01 March 2020 - 09:01 PM.

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#8 John Fitzgerald

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Posted 01 March 2020 - 08:41 PM

A friend has a 6" f/15 Jaegers, and it's excellent on planets.


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#9 Sky Muse

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Posted 01 March 2020 - 08:54 PM

Achromats have been around commercially since about 1750.  They've changed little if any since, and they were always longer.  Shorter, faster achromats made their debut in the 1980s or later.  

 

With an achromat, what you see is what you get: if it has a long tube, it will exhibit less false-colour; the longer the better.  If it has a short tube, it will exihibit a good deal of false-colour, particularly on brighter objects, like the planets.  False-colour blurs, smears the images.

 

This 90mm f/10 achromat is good for the planets...

 

100818a.jpg

 

This 80mm f/6 achromat is not as good for the planets...

 

Comet 46P-Wirtenan - 121618b.jpg

 

You may be drawn to the shorter achromats, but you'll be sacrificing optical performance for ergonomics.

 

The performance of a given achromat is determined by optical-physics, not by brand or price; if the doublet if well-figured across the board.


Edited by Sky Muse, 01 March 2020 - 09:09 PM.

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#10 drd715

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Posted 01 March 2020 - 09:29 PM

Probably F-12 in a 120 and F-15 in a 150 achro would be fair, but with ed glass and Lanthanum mate currently as as better combination you could really get a sharper image.

Problem is no one makes a long ED in those diameters. D&G made achros, but not currently available. There is the 102ED altair astro/ TS102ED, but 102 is a bit small in resolution diameter. Planets could use 3000mm fl but not so good in a refractor (except maybe folded).

Diameter and super long FL work well for bright planets. The problem with super long fl and high power is tracking and mount consideration. For practical use a 6 inch diameter F-12 is about as big as possible without having a permanent dome observatory.

In the real world I think the LZOS 130 - F9.25 would be most manageable, but it is a triple and very expensive.

So do you/ I sell off all our scopes to fund the LZOS 130 triplet or settle for a nice altair astro 102mm ED. $800 versus $8000.

I think someone needs to come up with a 130mm ED F-11 doublet FPL-53/ Lanthanum with a big supior focuser (3.7 inch hint Markus) under 2.5k$ - I could go for that.

Even a 140 F-10 ED doublet best glass. Still in the 1400/1430mm fl.

Dreams.

Sent from my SM-N950U using Tapatalk


Edited by drd715, 01 March 2020 - 09:36 PM.


#11 coopman

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Posted 01 March 2020 - 09:36 PM

I'd love to try this one:
https://www.landseas...ed-focuser.html
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#12 fishhuntmike

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Posted 01 March 2020 - 09:48 PM

I have been wondering this myself. 

 

I think I am going off the deep end in like 5 years and try to build an observatory with very large Istar 9.8" f11 R30 lens.  Order the lens sooner first just to make sure I got it, then build the observatory, source a tube and focuser, find a suitable mount ect.

 

I am hoping it to be my deep sky/planetary all-rounder. Maybe stop it down and/or use binoviewers

Sweet!!!!   I have the 220 f15 and 228 f7.7 just waiting for me to retire this fall.  Hopefully the f15 will be great stopped down a little on planets and i know it will be a killer on the moon.  Im going to start with the 228 first to replace my wood Berry style 6" f15 which is great on the moon and ok on planets.  I figure the 228 will simply be more versatile on deep sky stuff and can quickly stop it down to almost 5" f15 for great planet views if needed but use my existing tripod that i spent too many hours making.  The OTA will be cake to make.  I need to build a shop before considering the 220 f15 build which will also be alt-az but probably will be aluminum for the OTA.


Edited by fishhuntmike, 01 March 2020 - 09:49 PM.

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#13 drd715

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Posted 01 March 2020 - 09:48 PM

I'd love to try this one:
https://www.landseas...ed-focuser.html

Yes it is the best bargain out there.  Wish it was 120mm +.  Still I keep coming back to this cutie and saying I would like that. But it is about the same length as my 152ed f-8. I  bet it would be a fun visual scope.



#14 coopman

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Posted 01 March 2020 - 09:50 PM

Of course, triplets and ED doublet lenses can have very good color correction and tend to be quite good for planetary observing.  A lot depends on the type of glass used to make one or more elements of the lens.  I have had a couple of low focal ratio refractors with non-ED doublet objectives and they were not very good for planetary observing for the reasons that I have mentioned above.  I have never had a triplet objective scope, but they can show some CA as well, depending on the glass types used. A triplet does not guarantee that it will be color free.  I have several ED doublets and am very happy with their visual performance.  


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#15 Tyson M

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Posted 01 March 2020 - 09:54 PM

Sweet!!!!   I have the 220 f15 and 228 f7.7 just waiting for me to retire this fall.  Hopefully the f15 will be great stopped down a little on planets and i know it will be a killer on the moon.  Im going to start with the 228 first to replace my wood Berry style 6" f15 which is great on the moon and ok on planets.  I figure the 228 will simply be more versatile on deep sky stuff and can quickly stop it down to almost 5" f15 for great planet views if needed bit use my existing tripod that i spent too many hours making.  The OTA will be cake to make.  I need to build a shop before considering the 220 f15 build which will also be alt-az but probably will be aluminum for the OTA.

My ideas are still very much preliminary, but I have the land for the observatory and will have the budget for it soon.

 

I recall you saying you had a few large istar lenes.  You (and I if I follow the plan through), will likely have various design hurdles with the project to overcome but that's what makes it fun.  And the pay off is huge- an extremely large refractor experience. 

 

I will likely build a berry style mount but may bite the bullet  and pony up for an AP mount some day.



#16 coopman

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Posted 01 March 2020 - 09:54 PM

If you have never looked through a good ED doublet or triplet refractor, I urge you to do so.  You will love it. 


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#17 SteveG

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Posted 01 March 2020 - 10:05 PM

I had a 5” f9 Achro for a while. It didn’t perform well on planets. My ED 100 f9 does really well on planets. YMMV


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#18 photomagica

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Posted 01 March 2020 - 10:29 PM

As noted several times already, a not-too-fast achromat will give very satisfying planetary views. I've used both a 6"f15 achromat and an 8" f12.7 and on good nights both would deliver just about all that could be expected from the aperture. False color does reduce contrast a bit. One of the Baader filters may help. Before they existed I used to like a medium yellow filter on the 6" for the moon and some planetary and double star views. I find sometimes the Baader filters help an little and with other telescopes a lot. I like the semi-Apo filter but it seems to depend on the residual chromatic aberration and one's eyes so YMMV.

Before you buy go to star parties and try. You may find that a bit small apo will match what you can see with an achro. That said, a large aperture, long focal length achro on a REALLY SOLID mount is a very, very satisfying instrument.


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#19 Bomber Bob

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Posted 01 March 2020 - 10:29 PM

Yes, a well-made achromatic is a fine planetary instrument.

 

1950s Edmund 4" F15:

 

Edmund 4 - Saturn 20170707V05AS11.jpg

 

1970s Dakin 4" F10:

 

Dakin 4 - Jupiter (GRS) 20170609V04AS11.jpg

 

1960s Astro Optical 76mm F13:

 

Galactic 76 - Saturn 20170608V04AS11.jpg

 

1950s Unitron 75mm F15:

 

Unitron 142 - Jupiter (GRS) 20180607V04A64R05.jpg

 

1960s Hiyoshi 60mm F15:

 

M4380-Mars-20140426EP06A01CP16.jpg

 

Several of these images are from when I got my first digital imager, and was learning how to use the gear.  IOW:  I saw more at the eyepiece than I could capture.


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#20 Tropobob

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Posted 01 March 2020 - 10:33 PM

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.

Some of the better brands also have a range of budget scopes. These are generally best avoided if looking for a scope to perform well on planets. The same applies to anything less than F7 in an achro up to 70mm, more like F10 or more for anything 80mm or beyond. 


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#21 Bomber Bob

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Posted 01 March 2020 - 10:58 PM

D&G made some outstanding achromatics decades ago.  I ordered my 5" F10 in 1988 -- shortly after they ran their first ads in S&T.  Took about 8 months to get it.  Barry made it as CA-free as possible, and it wowed lots of folks at star parties -- Mars, Jupiter, Saturn at 400x and razor sharp.  But... it was a bit heavier than my APM 152ED; and, great as it was, it had more color than this F8 APO.  My Dakin 4" F10 has obvious false color, but the lens is so well made that it shows more fine detail than I expected.  Lots of factors affect high-power visual performance than just achro vs. APO, which is why I've kept some of my better examples of the old-fashioned kind.


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#22 JKAstro

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Posted 01 March 2020 - 11:07 PM

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.

I have a 4 inch Vixen achromat which is an old favorite of mine I can't part with.  Love those pinpoint stars.  In fact I just broke down and did something I've been telling myself not to do for years: I ordered a $300 Moonlight for it so I can use 2 inch eyepieces and my 2 inch prism diagonal.  I could have bought a used 4 inch AstroTech ED for $400 on classifieds this weekend.  But this wasn't about what made sense, it is about an old friend.  Anyway...

 

I also own a 4 inch triplet APO which does everything better than the Vixen except it takes longer to cool down.  Star colors are more true, and yes, planetary detail is better.  The same low contrast detail on Saturn and Jupiter might also be there in the Vixen, but with some of the blur from the out of focus light it is harder to see.

 

Not to say the Vixen is a dog on planets.  The Cassini division on Saturn is nice and sharp as are the shadows of Jupiter's moons as the cross the face.  But for the very fine low-contrast detail in Jupiter's clouds or Mars, the APO has it.

 

Now I would love to witness the views through a well made 6 inch F15.  But I wouldn't want to carry one.


Edited by JKAstro, 01 March 2020 - 11:09 PM.

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#23 Alan French

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Posted 01 March 2020 - 11:19 PM

Back in the days when the refractor choice was essentially limited to achromats, the typical long focus achromat was the preference and the dream of many lunar and planetary observers. The lack of central obstruction was considered a major advantage, the secondary color a tolerable problem at f/15 or longer. 

 

Today most people have voted, through their purchase decisions, for faster, easier to mount and manage apochromats. The availability of long focus, larger achromats is very limited, although used D&G achromats show up from time to time. 

 

Roland gives a nod to achromats in his CN article from 2005, "What is the Best Planetary Telescope?" 

 

See https://www.cloudyni...-telescope-r402

 

Of course the larger aperture, long focal length achromats best suited for planetary viewing are long, heavy, and require substantial mounts.

 

Clear skies, Alan


Edited by Alan French, 01 March 2020 - 11:20 PM.

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#24 Sketcher

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Posted 01 March 2020 - 11:53 PM

The question cannot be honestly answered with a simple "yes" or "no".  There are too many other variables to factor in.

 

What do you mean by "sharp"?  Do you want to talk about low-contrast detail or high-contrast detail?  (The distinction can make a difference in the answer.)  What kind of aperture do you have in mind?  What f-ratio?  What are your expectations?  What telescopes do you have experience with and what did you think of their planetary sharpness?  What was acceptable and what wasn't?

 

Some achromats can be quite nice planetary scopes (in some people's opinions), while others would be better suited for other purposes (in some people's opinions).

 

On the other hand, a telescope is a telescope; and any telescope will show you more than you'll see without it.  So if it's an achromat or nothing -- by all means, get the achromat.

 

Some people are far pickier than others when it comes to accepting this or that telescope for this purpose or for that purpose.

 

If you want to know about specifics -- a specific achromat, a specific planetary feature, perhaps compared to some other specific telescope, etc; Someone might be able to provide a more specific answer.  But for the question asked, as it was asked, one of the better answers might be:  "Yes for some, no for some, and maybe for some.

 

The question is a bit like asking:  "Are 22s accurate guns?"  Well, it depends -- on a lot of things.  Without having more in the way of specifics, the question has little meaning.


Edited by Sketcher, 01 March 2020 - 11:59 PM.

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#25 clearwaterdave

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Posted 02 March 2020 - 12:07 AM

You have gotten all the facts above.,I will just add that to me.,my achros gave fine sharp views of the planets.,( Jup.+Sat ).,.until I looked through something better.,

After that I found myself playing with the focuser more with the achro's.,trying to get it sharp.,

Then again.,there's only 2.,ok Mars.,3 planets that are more than a dot.,so buying a scope judged by it's planetary ability is limiting your choices for all the other goodies.,??maybe.,lol.,

  As Jon I. pointed out to me a few years ago.,you see the color because some of the light is not focused.,the light is the image.,cheers.


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