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Amazingly brutal optical test site. No SCT left alive!



 
 
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  #1  
Old July 28th 15, 04:45 AM posted to sci.astro.amateur
RichA[_6_]
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Default Amazingly brutal optical test site. No SCT left alive!

The astronomy nancy-boys at Sky and Tel would NEVER EVER do this!!!

http://r2.astro-foren.com/index.php/...nhofer-systeme
  #2  
Old July 28th 15, 06:17 PM posted to sci.astro.amateur
Chris.B[_2_]
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Default Amazingly brutal optical test site. No SCT left alive!

On Tuesday, 28 July 2015 05:45:40 UTC+2, RichA wrote:
The astronomy nancy-boys at Sky and Tel would NEVER EVER do this!!!

http://r2.astro-foren.com/index.php/...nhofer-systeme


While I am sure you were trying to stir up trouble for the SCT crowd and S&T's advertising sponsorship but there are many other publicised tests by Herr Rohr.

Wolfgang Rohr is quite an education in optics but not universally loved, nor loathed.

His 2013 test of an 8" short focus iStar objective and subsequent [and quite unexpected] publication online raised a few hackles as well as some eyebrows on the forums. The test link has now been removed by Rohr but a locked thread is still visible on CN.

http://www.cloudynights.com/topic/48...fie-01jan2015/

Short CN thread: Questions and answers on Rohr's methods:
http://www.cloudynights.com/topic/40...testing-setup/

My understanding is that Rohr tests privately-owned optics and instruments where the buyer has doubts as to the accuracy of the manufacturer's claims.

I also understand that he charges a fee for his tests as an independent optical consultant.

A certain, well-respected optician [MH] has voiced concerns as to Mr Rohr's methodology and results.

It is unfortunate that one must rely on inadequate online translation services to obtain the maximum value and enjoyment from Rohr's work.

Mr Zambuto enjoyed reading a private test of one of his fine mirrors sent to Rohr by its owner, without having previously warned Zambuto. The results are published by Zambuto:

http://zambutomirrors.com/zambutoopticalcd.html

Yet another [positive] test of iStar optics:

http://www.cloudynights.com/topic/42...wolfgang-rohr/

It would be interesting to see a comparison test of exactly the same optics by another independent tester.

Orion Optics [UK] will independently test optics for a not-reasonable price:

http://www.orionoptics.co.uk/OPTICS/...telescope.html

20% VAT is additional to the published list.
  #3  
Old July 29th 15, 04:39 AM posted to sci.astro.amateur
RichA[_6_]
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Default Amazingly brutal optical test site. No SCT left alive!

On Tuesday, 28 July 2015 13:17:06 UTC-4, Chris.B wrote:
On Tuesday, 28 July 2015 05:45:40 UTC+2, RichA wrote:
The astronomy nancy-boys at Sky and Tel would NEVER EVER do this!!!

http://r2.astro-foren.com/index.php/...nhofer-systeme


While I am sure you were trying to stir up trouble for the SCT crowd and S&T's advertising sponsorship but there are many other publicised tests by Herr Rohr.

Wolfgang Rohr is quite an education in optics but not universally loved, nor loathed.

His 2013 test of an 8" short focus iStar objective and subsequent [and quite unexpected] publication online raised a few hackles as well as some eyebrows on the forums. The test link has now been removed by Rohr but a locked thread is still visible on CN.

http://www.cloudynights.com/topic/48...fie-01jan2015/

Short CN thread: Questions and answers on Rohr's methods:
http://www.cloudynights.com/topic/40...testing-setup/

My understanding is that Rohr tests privately-owned optics and instruments where the buyer has doubts as to the accuracy of the manufacturer's claims.

I also understand that he charges a fee for his tests as an independent optical consultant.

A certain, well-respected optician [MH] has voiced concerns as to Mr Rohr's methodology and results.

It is unfortunate that one must rely on inadequate online translation services to obtain the maximum value and enjoyment from Rohr's work.

Mr Zambuto enjoyed reading a private test of one of his fine mirrors sent to Rohr by its owner, without having previously warned Zambuto. The results are published by Zambuto:

http://zambutomirrors.com/zambutoopticalcd.html

Yet another [positive] test of iStar optics:

http://www.cloudynights.com/topic/42...wolfgang-rohr/

It would be interesting to see a comparison test of exactly the same optics by another independent tester.

Orion Optics [UK] will independently test optics for a not-reasonable price:

http://www.orionoptics.co.uk/OPTICS/...telescope.html

20% VAT is additional to the published list.


I think the tests on the page are legit. It's pretty hard to make a mistake in set-up that shows a zonal error. Also, it's good to have people with no axe to grind doing this. His test of the 130mm Vixen showed a fantastic result while he doesn't spare other vaunted makers of scopes.
  #4  
Old July 29th 15, 08:59 AM posted to sci.astro.amateur
Chris.B[_2_]
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Default Amazingly brutal optical test site. No SCT left alive!

On Wednesday, 29 July 2015 05:39:12 UTC+2, RichA wrote:

I think the tests on the page are legit. It's pretty hard to make a mistake in set-up that shows a zonal error. Also, it's good to have people with no axe to grind doing this. His test of the 130mm Vixen showed a fantastic result while he doesn't spare other vaunted makers of scopes.


I agree, but would enjoy hearing one of our resident optical expert's opinions on Rohr's work. If anything, I feel Rohr is helping to expose the variability of optical surfaces from some/many recognised sources.

This is a market where the buyer is [almost] powerless to test the manufacturer's claimed figures for accuracy and correction of the "problem" aberrations. The owner may well do star tests but, due to the level of interpretation required, not to mention the variability of seeing conditions, the majority are unlikely to be able to put firm figures on what they see.

There is a strong degree of "HiFi" sales hype in the optical instrument market. Every maker claims to make the best but nobody [other than Rohr] is making a habit of publicly exposing the blatant hype. Unfortunately the "double blind" tests, with which disciplined experts undermine almost 100% of HiFi manufacturer's claims as completely false, are not easily arranged with optical instruments. Only the expensive tools and [hopefully] the expertise of Rohr can remove the subjective "product loyalty" elements from the manufacturer's sales hype.

We all know that rare night of wonderful seeing when our normally "fuzzy" instruments suddenly reveal planetary detail we never [previously] knew existed. Only then can we truly appraise our optics by pushing them to their theoretical limits and stay up all night.

For the rest of the time being merely "diffraction limited" is arguably good enough. But what if those rare nights never present themselves in our continually fuzzy instruments? What then? The local consumer protection office is extremely unlikely to be able to help.
  #5  
Old July 30th 15, 03:57 AM posted to sci.astro.amateur
RichA[_6_]
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Posts: 1,076
Default Amazingly brutal optical test site. No SCT left alive!

On Wednesday, 29 July 2015 03:59:35 UTC-4, Chris.B wrote:
On Wednesday, 29 July 2015 05:39:12 UTC+2, RichA wrote:

I think the tests on the page are legit. It's pretty hard to make a mistake in set-up that shows a zonal error. Also, it's good to have people with no axe to grind doing this. His test of the 130mm Vixen showed a fantastic result while he doesn't spare other vaunted makers of scopes.


I agree, but would enjoy hearing one of our resident optical expert's opinions on Rohr's work. If anything, I feel Rohr is helping to expose the variability of optical surfaces from some/many recognised sources.

This is a market where the buyer is [almost] powerless to test the manufacturer's claimed figures for accuracy and correction of the "problem" aberrations. The owner may well do star tests but, due to the level of interpretation required, not to mention the variability of seeing conditions, the majority are unlikely to be able to put firm figures on what they see.

There is a strong degree of "HiFi" sales hype in the optical instrument market. Every maker claims to make the best but nobody [other than Rohr] is making a habit of publicly exposing the blatant hype. Unfortunately the "double blind" tests, with which disciplined experts undermine almost 100% of HiFi manufacturer's claims as completely false, are not easily arranged with optical instruments. Only the expensive tools and [hopefully] the expertise of Rohr can remove the subjective "product loyalty" elements from the manufacturer's sales hype.

We all know that rare night of wonderful seeing when our normally "fuzzy" instruments suddenly reveal planetary detail we never [previously] knew existed. Only then can we truly appraise our optics by pushing them to their theoretical limits and stay up all night.

For the rest of the time being merely "diffraction limited" is arguably good enough. But what if those rare nights never present themselves in our continually fuzzy instruments? What then? The local consumer protection office is extremely unlikely to be able to help.


It would be like asking them to arbitrate a patent dispute. None would have the skill.
  #6  
Old July 31st 15, 09:29 AM posted to sci.astro.amateur
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Default Amazingly brutal optical test site. No SCT left alive!

On Wednesday, July 29, 2015 at 3:59:35 AM UTC-4, Chris.B wrote:

For the rest of the time being merely "diffraction limited" is arguably good
enough. But what if those rare nights never present themselves in our
continually fuzzy instruments? What then? The local consumer protection office
is extremely unlikely to be able to help.


Buy and use a somewhat larger telescope with good, even if not truly excellent, optics.

The optics in my first telescopes were acceptable. However even as a beginner I realized that I needed a bigger telescope, not a better telescope.
  #7  
Old August 3rd 15, 10:48 AM posted to sci.astro.amateur
Chris.B[_2_]
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Default Amazingly brutal optical test site. No SCT left alive!

On Friday, 31 July 2015 10:29:33 UTC+2, wrote:
Buy and use a somewhat larger telescope with good, even if not truly excellent, optics.

The optics in my first telescopes were acceptable. However even as a beginner I realized that I needed a bigger telescope, not a better telescope.


Size certainly matters but is increasingly "seeing" sensitive with increased aperture. Larger mirrors [and lenses] tend towards shorter focus just to make them physically manageable. Faster mirrors will exhibit coma unless this is optically corrected with an add-on. Faster mirrors require much more careful collimation and repeated attention to maintain it. They have a shallower depth of focus requiring slow motion focusers and repeated re-focusing during observation. Longer focus mirrors and lenses are less sensitive to focusing error but are much more difficult to mount because of their much higher moment arm. The primary lens or mirror is usually situated at the extreme end of the OTA.

Larger mirrors [and lenses] have more mass and will often suffer from slower cool down to ambient temperatures or cooling, evening temperatures. Ventilation fans are increasingly used to aid more rapid cool down. While, at the same time, primary mirror blanks are becoming thinner, conical or even cellular to reduce their thermal mass.

Many observers enjoy fine views in their smaller instruments while the larger instruments more often languish in poor seeing. "Diffraction limited" is a minimum optical quality. For the finest lunar and planetary detail premium optics are still necessary. A fine lens or mirror will hold a higher magnification before the image breaks down *provided the seeing allows it.* Telescope reviewers and new owners of premium optics regularly attest to this fact. This does not alter the optic's aperture-related resolution but sometimes seems like it.
  #8  
Old August 4th 15, 02:27 AM posted to sci.astro.amateur
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Default Amazingly brutal optical test site. No SCT left alive!

On Monday, August 3, 2015 at 5:48:11 AM UTC-4, Chris.B wrote:
On Friday, 31 July 2015 10:29:33 UTC+2, wsne... wrote:


Buy and use a somewhat larger telescope with good, even if not truly excellent, optics.

The optics in my first telescopes were acceptable. However even as a beginner I realized that I needed a bigger telescope, not a better telescope.


chrisbcritter's irrelevant comments and misleading half-truths deleted

Many observers enjoy fine views in their smaller instruments while the larger
instruments more often languish in poor seeing.


Incorrect. The larger instruments generally provide superior views, regardless of seeing.

"Diffraction limited" is a
minimum optical quality. For the finest lunar and planetary detail premium
optics are still necessary.


Incorrect. A diffraction limited scope will easily beat a so-called "premium optics" scope of somewhat smaller aperture.

A fine lens or mirror will hold a higher
magnification before the image breaks down *provided the seeing allows it.*


That is a nonsensical statement.

Telescope reviewers and new owners of premium optics regularly attest to this fact.


You did not state a fact.

This does not alter the optic's aperture-related resolution but
sometimes seems like it.


Then obviously those reviewers and "new owners" are fooling themselves.

  #9  
Old August 4th 15, 11:37 AM posted to sci.astro.amateur
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Default Amazingly brutal optical test site. No SCT left alive!

On Tuesday, August 4, 2015 at 1:34:17 AM UTC-4, Chris.B wrote:
On Tuesday, 4 August 2015 03:27:32 UTC+2, wsne... wrote:

Then obviously those reviewers and "new owners" are fooling themselves.


Thus spake Solomon ø' Zarathustra, from his subterranean bunker, on the subject of observational, optical crutches.


If you believe what some of those reviewers and "new owners" are saying then they are fooling you.

  #10  
Old August 4th 15, 11:48 AM posted to sci.astro.amateur
Chris.B[_2_]
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Default Amazingly brutal optical test site. No SCT left alive!

On Tuesday, 4 August 2015 12:37:04 UTC+2, wrote:
If you believe what some of those reviewers and "new owners" are saying then they are fooling you.


And themselves, no doubt?

This, despite several lifetimes of critical observational experience with a whole variety of instruments and sizes?

Or are you merely arguing for the sake of it?

What is your own *direct* experience of making side by side telescope comparisons under a wide variety of seeing conditions?
 




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