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What happened to the big achromats?

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#1 billastro

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Posted 28 May 2023 - 05:04 PM

I finally decided to get a fast 5”-6” achromatic scope for visual use and I can’t find one anywhere. e.g. - Orion says the Explore Scientific AR152 won’t ship until November! What’s going on? Supply chain issues? Trade barriers? or just the shifting tides of popularity?



#2 aneeg

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Posted 28 May 2023 - 05:15 PM

Altair has their 152 achro in stock.

 

Arne



#3 Cbaxter

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Posted 28 May 2023 - 05:40 PM

ED doublets are so much cheaper than they used to be, even with recent inflation, that there may not be a worthwhile market for some of the old yard canon achromats. For the longest time I had and loved a C6-R 6" f8. I thought the CA was tolerable and didn't think it impacted DSO views much or at all. I know better now. They just don't handle magnification well at all and the best views it ever gave me were still soft compared to even the cheapest ED scope I've owned. Achromats do provide a cheap path to low-power wide-field views, but so can a cheap small apature ED refractor and with less CA. My first ED scope was a 110mm f6 fpl-53 doublet. After using it mounted side-by-side with my C6-R for over a year, I finally sold the C6-R. I compared them in all sorts of ways and for a long time really wanted the 6" achromat to keep a useful place in my lineup. The 6" achromat always had a brighter image at compared magnifications but the 110mm ED doublet always, always, had a sharper image with a more obvious "snap to focus" and SIGNIFICANTLY less CA than the achromat. In the end, the brighter image was not worth the degraded imaged quality. And no, a long pass yellow filter did not turn the achromat into an ED. What sealed the fate of the 6" achromat was how heavy and long it was compared to the smaller ED scope. If I want bright views of faint DSO, I'll be using a large reflector. Refractors just cannot compete when it comes to apature/cost for DSO,s (when seeing permits). And low power wide fields are bright enough even in smallish ED refractors.

Edited by Cbaxter, 28 May 2023 - 05:43 PM.

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#4 vtornado

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Posted 28 May 2023 - 05:52 PM

I think vendors are catering to demand and demand is for imaging, so small fast refractors is where the attention is going.  I run public star parties, and would love to have a large

achro because it would be a kid magnet.  On the other hand, it has to be cheap.  I cant tie up a bunch of cash in a scope that is basically not really used.


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#5 Kitfox

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Posted 28 May 2023 - 05:54 PM

I have been seriously debating making a deal with Markus Ludes on one of those big Zeiss objectives he is listing on AM.  I just hesitate at the size of the building it would take to hold it…


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#6 scngc7317

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Posted 28 May 2023 - 06:10 PM

My ISTAR F-15 = 6"

 

IMG 3616
 
 
Lunar Rover Tracks in poor seeing rofl2.gif
 
584391main M168000580LR ap17 area nolabel

 


Edited by scngc7317, 28 May 2023 - 06:23 PM.

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#7 sdedalus83

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Posted 28 May 2023 - 06:29 PM

JOC is in Guangzhou which was hit hard by Covid restrictions. Vixen is also seriously backlogged due to component shortages.



#8 Redbetter

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Posted 28 May 2023 - 06:31 PM

Imaging has to be one of the larger hurdles for a 5 or 6" achromat.  Couple that still needing a mount that can properly handle the relatively heavy tube with a focal length nearing 1000mm.   

 

So for imagers I don't see any attraction to this size/ratio achro.  And for visual observers it would seem to make more sense to have an ~5" ED doublet or triplet rather than a 6" achro.  Focal lengths (TFOV) will be essentially the same, and the difference in quality/contrast of the view is likely to be sufficient for the difference in overall brightness.  


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#9 CHASLX200

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Posted 28 May 2023 - 06:46 PM

I have been seriously debating making a deal with Markus Ludes on one of those big Zeiss objectives he is listing on AM.  I just hesitate at the size of the building it would take to hold it…

You can keep it at my house.  Kinda like big old school EQ mounted Newts that went away in the 80's, so the same for slow Achro's.


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#10 dnrmilspec

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Posted 28 May 2023 - 06:51 PM

I think vendors are catering to demand and demand is for imaging, so small fast refractors is where the attention is going.  I run public star parties, and would love to have a large

achro because it would be a kid magnet.  On the other hand, it has to be cheap.  I cant tie up a bunch of cash in a scope that is basically not really used.

Absolutely true.  I have the aforementioned ES-152 AR with a really nice Moonlight focuser on it.  (Two actually and one is for sale in the classifieds right now.)  They are absolutely kid-and-everyone-else magnets at star parties.  That scope on the EQ6R mount is pretty impressive.  The fancy focuser really ups the enjoyment from this scope.  But even with the Moonlight you are still talking 1/4 the price of a same size APO.

 

People at star parties are not as particular about false color as many of us are.  And if the truth were known these scopes are just stunning on most subjects.  There are many of us here who remember when APO scopes were as scarce as can be.  And very expensive.  Even today the least expensive 6" APOs are north of $4000.00.  Nearly 10X more expensive than the average used 6" Achromat goes for. 

 

And are they 10 times better?   Well that depends.  On the double cluster when equipped with a top drawer diagonal and good eyepiece?  Little to nothing to show for your extra $3000.00 the APO is going to set you back.  On Jupiter?  Better to much better in the APO.  Still some beautiful views though.  A little purple but you ought to see Saturn....And that is the rub.  You don't buy this scope to compete with a 6" Apochromat on planets.  And, very frankly, big APOs are hard pressed to compete with a really big reflector costing a fraction of the price.

 

It is sad that many of us see this as some kind of competition.  It really isn't.  The big ES is sitting on a scope cart in my garage right now.  I intend to take it out this PM for a quick look around our great Arizona skies.  I have 12 or so scopes from which to choose.  The fast, wide achromat is a legit choice.  It really puts up some great images.  Does it compete with the Astrphysics or Takahashi Apochromats?  Yes it does.  And quite well actually when pointed at an appropriate target.  I am not selling my APOs.  I will continue to use them.  But it would be a real shame for someone to walk past one of these and miss what Ed Ting calls "that refractor magic" because $10K is out of the budget.  Whoever gets the one I have for sale is getting a really nice scope.  And if they choose to take it to Vtornado's star parties will be the busiest guy there. 

 

Final comment.  MANY of the folks who enjoy looking through the yard cannon ARE larger APO owners.  And when seeing what they can get for a lot less money, often walk away shaking their heads.  Budget almost always matters.  I could make a very good case for having the big achromat, a top-drawer set of eye wear and a robust mount as opposed to an under-mounted smaller APO, especially starting out.  The mount and eyepieces go on forever if and when one decides to pull the trigger on really expensive glass.

 

 

 

 


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#11 sdedalus83

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Posted 28 May 2023 - 06:58 PM

I have been seriously debating making a deal with Markus Ludes on one of those big Zeiss objectives he is listing on AM.  I just hesitate at the size of the building it would take to hold it…

Commission a folded tube . They had that listed as an option for the 6” F24 Lichtenecker objective they had and their folded 10” TMB was really slick.


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#12 Kitfox

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Posted 28 May 2023 - 06:59 PM

That 200mm objective has a THREE METER focal length. that would make the OTA well over 10 feet long…. Tell me that would not be exciting at a star party lol.gif

 

 

You can keep it at my house.  Kinda like big old school EQ mounted Newts that went away in the 80's, so the same for slow Achro's.


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#13 Kitfox

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Posted 28 May 2023 - 07:01 PM

That’s a great idea, but not sure I could force myself to put Zeiss glass in anything but a classic tube…wink.gif

 

 

Commission a folded tube . They had that listed as an option for the 6” F24 Lichtenecker objective they had and their folded 10” TMB was really slick.


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#14 CHASLX200

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Posted 28 May 2023 - 07:02 PM

That 200mm objective has a THREE METER focal length. that would make the OTA well over 10 feet long…. Tell me that would not be exciting at a star party lol.gif

It sure would, but not gonna fit in the new Vette.


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#15 sdedalus83

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Posted 28 May 2023 - 07:17 PM

That’s a great idea, but not sure I could force myself to put Zeiss glass in anything but a classic tube…wink.gif

970001-1.jpg


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#16 Kitfox

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Posted 28 May 2023 - 07:20 PM

Is the eyepiece at the end of the polar axis?  That is a system!

 

 

Wow, I found it!  https://astromart.co...coude-refractor


Edited by Kitfox, 28 May 2023 - 07:22 PM.


#17 Thomas_M44

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Posted 28 May 2023 - 08:07 PM

Is the eyepiece at the end of the polar axis?  That is a system!
 
 
Wow, I found it!  https://astromart.co...coude-refractor


You’d be the first kid on the block to have one of *those* ;-)

Edited by Thomas_M44, 28 May 2023 - 08:07 PM.

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#18 kwyjibo

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Posted 28 May 2023 - 08:41 PM

The C6R is available here.

https://telescopes.n...e-assembly.html



#19 Redbetter

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Posted 28 May 2023 - 09:31 PM

Absolutely true.  I have the aforementioned ES-152 AR with a really nice Moonlight focuser on it.  (Two actually and one is for sale in the classifieds right now.)  They are absolutely kid-and-everyone-else magnets at star parties.  That scope on the EQ6R mount is pretty impressive.  The fancy focuser really ups the enjoyment from this scope.  But even with the Moonlight you are still talking 1/4 the price of a same size APO.

 

People at star parties are not as particular about false color as many of us are.  And if the truth were known these scopes are just stunning on most subjects.  There are many of us here who remember when APO scopes were as scarce as can be.  And very expensive.  Even today the least expensive 6" APOs are north of $4000.00.  Nearly 10X more expensive than the average used 6" Achromat goes for. 

 

And are they 10 times better?   Well that depends.  On the double cluster when equipped with a top drawer diagonal and good eyepiece?  Little to nothing to show for your extra $3000.00 the APO is going to set you back.  On Jupiter?  Better to much better in the APO.  Still some beautiful views though.  A little purple but you ought to see Saturn....And that is the rub.  You don't buy this scope to compete with a 6" Apochromat on planets.  And, very frankly, big APOs are hard pressed to compete with a really big reflector costing a fraction of the price.

I guess if one assumes they must have a 6" and only compares to an APO this might be true.  But when I have looked at both 5" and 6" ED's, it became apparent to me that there was a step change in mounting requirements in getting the 6".  So I went the AT125EDL route with case for about  $850 more than what I see the AR152's listed for.  No need to upgrade the 2.5" focuser (so the differential might be considerably less.)   I have it mounted on an LX70 with dual drive which ran me $285 delivered.   No need for a $2,000 mount.  

 

I haven't compared a fast 6" achro side-by-side with the 125EDL, but I would be surprised if the achro did as well for planets, and I doubt it would show me more on DSO's.  There is a penalty to be had for moving well out of the diffraction limited range.  A CA ratio of 1.1 or less is pretty damaging to the visual image from what I have seen, and filters don't fix that for higher resolution observing.  A 6" would do better for emission nebula with line or narrow band filters.  

 

What I have compared is the Orion ED80 vs. good samples of an 80 f/11.3 achro, and 80 f/5 (CA ratios of 3.6 and 1.6 respectively.)  The objectives were good enough that I converted both of the achros to 2" focusers, and move the baffle of the f/5 to make use of it.  The f/11 achro tops out for detail at a lower mag level than the ED80, somewhat less than the AT72EDII,  And the 80 f/5 suffers much more in this regard.  I've tried filters, but the optimums were still the same for detail in both cases.  My AT60ED partially resolves the same globulars that I have partially resolved with an 80 f/5 in the past (although that 80 f/5 is not as sharp as the one I used for the 80mm comparisons.)  For planetary detail I'll take the 60ED over the 80 f/5 achro.  


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#20 Cbaxter

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Posted 28 May 2023 - 09:56 PM

Does it compete with the Astrphysics or Takahashi Apochromats? Yes it does. And quite well actually when pointed at an appropriate target.

Maybe on some targets but not many. Even on DSO where CA isn't apparent, the chromatic blur degrades the image. Many DSO's are broadband, especially galaxies and that unfocused light can never be recovered. It is lost information that only softens the image. A long pass yellow filter can filter out the unfocused light but that light will be completely absent from the image. It's physics. The achromat, especially a fast 6", physically will never have as much of the visible spectrum sharply focused. I don't know that many folks would agree that an achromat competes with a similar sized Tak or AP triplet. As for the cost, a ~5" fpl53 doublet or fcd1/fpl51 triplet can be had for far less then that $4k mark you mention. I'd recommend a 5" cheap ED over a 6" achromat any day. The CA in my 6" f8 achro was terrible compared to my current fcd1 5" triplet. I don't even care to know how much worse it would be in a fast f5-f6.5 achro. And as far as the wide-field low power argument, a smaller APO triplet will physically show a better more sharply focused image with similar fields of view to the large achromat. The larger achro is brighter at comparable fov but the brightness is marred by severe chromatic abortions.

Edited by Cbaxter, 28 May 2023 - 10:02 PM.

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#21 dnrmilspec

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Posted 28 May 2023 - 10:40 PM

I get all of the boilerplate arguments.  The thing is that as far as general public viewing is concerned they do not hold up in actual practice.  Sure there are differences but under normal seeing conditions and absent a + b comparisons, the views one gets from a good achromat are just fine.  Very pleasing.  And I can say unequivocally, the guests love them.  And so do many of the experienced viewers who stop by to see.

 

I own APO scopes and use them frequently.  This is not my first rodeo.  I also remember when a true APO was FAR more expensive than it is now.  And as rare as hen's teeth.  We used and loved achromatic scopes big and small.  They still have their place. 

 

So bluntly, spare me the physics lesson.  I am not your enemy and this is not a competition.  My stable has included/includes AP and Takahashi refractors as well as more modest ED scopes.  They are wonderful and we who have owned any them are fortunate.   They are not for everyone.  The question came up about big refractors for outreach.  This is a site that frequently looses itself in shear gearheadedness.  A general friend of mine put something on his challenge coins.  It reads:  The main thing is to always remember what the main thing is.   So when people are enjoying what they are seeing, do not harsh their buzz unless you are willing to stroke the check to pay for your conceit. 


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#22 Redbetter

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Posted 29 May 2023 - 01:30 AM

The comparisons do hold up for visual in actual practice.  That is the point.  It doesn't matter what the general public is flocking to when they see a group of scopes set up, physics isn't a popularity contest. 

 

The question of the thread was "what happened to the big achromats" and the simplest answer is that they have been supplanted by affordable ED/APO's for both visual and imaging.  These don't have to be as large in aperture to do the same job, and better in some ways.  And they cost a fraction of what the premium APO's cost.


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#23 Cbaxter

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Posted 29 May 2023 - 02:23 AM

I don't think anyone is intentionally trying to be a downer on someone else's buzz. However, when claims are made such as a rather fast 6" achromat competing with a top-tier apo, expect some ruffled feathers to chime in. That's just the way it is. I don't hate achromats. On the contrary, I like them a lot. I no longer own any but I have fond memories of them and my first ever astro photo was imaged with an Orion 120st f5 achromat and a 495 long pass filter. I still show the image to folks because I think it was a wonderful image for such humble gear. I never could get the colors correct though, because the blue was filtered out since it wasn't in-focus anyway.
https://telescopius....vision_id=83639
It may seem like I am anti-achromat but I am most definitely not. That doesn't change the fact that a cheap modern ED scope will generally outperform some of the best achromats. A 5" apo can be had for just a bit over twice the cost of the ES AR152 and yes, I would say the views are easily "twice" as good, even with the apature disadvantage. Unless perhaps significant chromatic distortion is pleasing to the viewer...

Edited by Cbaxter, 29 May 2023 - 02:25 AM.


#24 Skywatchr

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Posted 29 May 2023 - 02:50 AM

This.....  And people get too emotional over it...  Unfortunately it happens in nearly every thread.  There is way too much perfectionism in a simple hobby of enjoying the Heavens Above by whatever means one can afford, or desire.



  This is a site that frequently looses itself in shear gearheadedness.  A general friend of mine put something on his challenge coins.  It reads:  The main thing is to always remember what the main thing is.   So when people are enjoying what they are seeing, do not harsh their buzz unless you are willing to stroke the check to pay for your conceit. 


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#25 CHASLX200

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Posted 29 May 2023 - 05:23 AM

My two CR6's were great deep sky scopes. Dark field background and snappy contrast at lower powers. But they were a color monster on the moon and no way i could handle that much color.  Three things i can't deal with, Coma, FC and Color. 


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