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Zeiss sample variation test by Jan M. (1 Viewer)

K

kabsetz

Well-known member
Jan Meijerink has tested side-by-side five samples of the Zeiss 85 FL, and has now posted the results on www.tvwg.nl

He hints at this being the first in a series of similar tests.

You'll find it under "testrapportten" "telescopes." He includes digital photos of a resolution target through all five at 40x and 60x magnifications. Enjoy!

Kimmo
 
Kimmo,

Thanks for the link. No surprises there for me. Of the six 85mm Diascopes I've tested one was a lemon about as bad as the worst of this group and another was almost as bad. The best one I've seen was actually a bit better than any of these, with resolution (calculated in the same way) of about .85 arcseconds. I suppose it should be noted that none of these telescopes, including the Kowa, is all that great. All of them fall short of the Rayleigh limit (85mm=.81 arcsec, 88mm=.78 arcsec). Now, it would be interesting to see photos of star tests of these scopes so we could know just why they are performing as they do.

Henry
 
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Looking at the resolution chart more closely shows some interesting things. You can easily see that 20x is not very useful for evaluating scopes. It does not allow the resolution difference between a lemon and a good sample to be seen. 30x has some unpredictable results, perhaps reflecting the effects of different types of defects (for instance astigmatism vs missalignment) or maybe a different mix of multiple defects and aberrations. This is where a star test would be informative.
 
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Henry,

As you indicate, and as Jan says in his introduction, he uses what has been called "single line formula" whereby the arcsecond vaule refers to the width of a single black or white line, not the width of the pair. This just as a clarification to other readers who might have difficulty following our discussion.

In his sampling of five, even if the worst unit is left out, there is still a difference of almost 10% between the best and the second-worst unit, and more than ten to the best Zeiss unit he mentions having tested previously.

Even without a star test at least the worst unit shows astigmatism, which you can see in the horizontal bars being much more clear than the vertical in all groups. The fifth Zeiss (the images fartherst to the right) show color fringing to the line patterns, which he mentiones in the text.

I agree that it seems that none of these is really close to diffraction limited. Further evidence comes if you compare these images to Jan's images in the Kowa 883 test report, where the same Kowa 883 which has the best test results here falls slightly short by comparison to his unusually low-aberration 823.

Kimmo
 
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kabsetz said:
Henry,

As you indicate, and as Jan says in his introduction, he uses what has been called "single line formula" whereby the arcsecond vaule refers to the width of a single black or white line, not the width of the pair. This just as a clarification to other readers who might have difficulty following our discussion.

In his sampling of five, even if the worst unit is left out, there is still a difference of almost 10% between the best and the second-worst unit, and more than ten to the best Zeiss unit he mentions having tested previously.

Even without a star test at least the worst unit shows astigmatism, which you can see in the horizontal bars being much more clear than the vertical in all groups. The fifth Zeiss (the images fartherst to the right) show color fringing to the line patterns, which he mentiones in the text.

I agree that it seems that none of these is really close to diffraction limited. Further evidence comes if you compare these images to Jan's images in the Kowa 883 test report, where the same Kowa 883 which has the best test results here falls slightly short by comparison to his unusually low-aberration 823.

Kimmo
Click to expand...
Hi Kimmo,
Is it possible to read these tests in english.
fiddler
 
Thank you Kimmo for advice.
While the results aren´t really a surprise the work of Jan Meijerink stays to be simply great. This is the first serious trial to analyze the phenomenon of sample variation in high quality optics I have seen so far. Maybe the manufactorers should be more careful in the future. One could understand a lack in quality in production as a hidden way of cost saving. Happy members of the Twentse Vogelwerkgroep! Jan does the intake controll of scopes for them by himself.

Steve
 
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Fiddler,

Unfortunately, Jan's work is only available in Dutch - serves as an incentive for learning his fine language. A full translation would be a fair amount of work, and publishing it in any form would be an infringement of Jan's copyright.

Kimmo
 
For comparison this is how the two translate the first paragraph of the article:

www.freetranslation.com:
Although by telescopes of the topmerken scarcely of varition in optical quality talk is, comes this by the telescopes regularly for. A small spacing is acceptable, but sometimes slips there a specimen through the end control that actual disapproved should become. By some cheap brands is not the varition yet larger, what for me also a reason is this equipment to test.
Click to expand...

babelfish.altavista.com:
Although at binoculars of the top marks hardly of variatie in optical quality talk is, this occurs at telescopes regularly. A small spacing is acceptable, but sometimes skids there a copy by the final inspection which would have in fact disapproved. At some cheap marks the variatie is still larger, which for me a reason is not these test equipment.
Click to expand...

Neither are close to perfect, but babelfish seems to make less of a mess overall.
 
Really interesting stuff this! While some of our top optics reviewers have repeatedly flagged the issue of sample variability, a thorough report like this should surely put the cat amongst the pigeons! Perhaps I'm naive but I actually think it's our right as consumers to expect a better standard of quality control at this level. It would be nice to think that as this story (hopefully) gains momentum at least one of the major manufacturers will up the QC ante forcing the rest to follow. If not, maybe some enterprising retailer will start to pre-select scopes as they arrive and offer some kind of consumer guarantee of sample quality! Bet they'd corner the market overnight if they did...or perhaps the manufacturers would simply stop supplying them!! (oooh, cynical!)
I must admit, if I was in the market for a brand new top-end 80mm+ scope (I wish!!) I'd be wanting to make certain sure I had a good un for my 1200-1500 quid!! And I'd be a pain in the whatsit for any poor retailer having to line up 3 or 4 samples of my chosen scope to compare!
But what to look for? I understand the star test idea but beyond this I wouldn't know how to make any meaningful assessment. Stringent 'lab' tests are one thing, trying to make an assessment in the shop is another!! So, perhaps one of our forum optics experts might suggest ways to pick out the cherries in the shop environment? If birders learn to identify lemons as well as locustellas then manufacturers are going to have to stop shipping them (lemons, not locustellas...mind you, nice marketing ploy that...Gray's Gropper free with an 883!! ;) )
 
Hi Jan,

I think that he used the USAF 1951 type test. I think that you can buy this test from special optical companies in Europe or USA. I have been searched on the web many times different optical tests, and I found that for the best results you have to buy one original sample (you can find uploaded test in different photo sites, but without a good printer there is no possibility to print correctly them). There are many variations, depending on the qualitiy of the drawings, and holding material (paper, metal film) and size.

Best regards: Krisztián


BirderJan said:
Does anyone know where to get the testsign he used? Perhaps I could make one myself. Whats the width of the lines?

Jan
Click to expand...
 
Jan,

Mr. Meijerink's test target is made by himself and is not available. Edmund scientific (you can find it on the net and it has a branch in U.K. that sells to Europe) sells various versions of an USAF resolution target as well as some other targets.

Kimmo
 
Years ago I evaluated several 77mm Leica Apo Televid spotting scopes using resolution charts and star tests. In a telephone conversation, a Leica technician mentioned that the benchmark for this optic was 1/2 wave. That is essentially what I observed in the poorest unit. Images started to soften above 20x. Besides considerable s.a., the poorest unit also exhibited astigmatism. I would rate the best one at about 1/6 to 1/8 wave - it showed almost perfect diffraction patterns and held excellent image sharpness and contrast well past 100x (with a specially adapted eyepiece). Resolution figures can be misleading by failing to relate to the actual visual image presented by the optic. For example, if there is significant spherical abberation present, the optic may still resolve quite well but the image will lack contrast and seem 'washed out', as power is increased - Herb
 
Nice test but it only compares the body or tests the all set - body+zoom (I didn't tried the web translators...)? I.e. the zoom eyepiece was always the same or not? Variations in eyepiece quality also can induce variations on the all set results.

David
 
David,

I don't know if Jan used one or more zoom eyepieces in his test, but although your concern about an unknown variable is valid in theory, my experience and testing has shown that in practice it makes no difference when it comes to eyepiece samples. I have twice tested a bunch of zooms on a single, high-quality-sample scope. The first time they were some six or so Leica zooms on a Leica Apo-Televid, and the second time they were some dozen Nikon MC II zooms on the ED 82 A. In neither test did I find a single eyepiece specimen that would have changed the resultant eyepiece-scope resolution figures by a detectable amount one way or the other, and in the end picked a "winner" mainly by a very subjective and rather unreliable "ease-of-view-feel." With the eyepieces, I doubt if, after having picked the "best" and the "worst" specimen, I could have reliably been able to tell them apart in a random blind test. The differences between scope specimen, on the other hand, are usually painfully obvious.

So, I'm sure they may be an occasional lemon among eyepieces, and I have certainly see some that have had specs of dirt on some inside elements straight out of the box, but generally speaking telescope eyepieces are the one optical item I personally would dare to buy unseen and untested.

Kimmo
 
This is Steve Ingraham's response to the tests:

I will withhold any real comment on that particular test until I have seen at least two more tests of other brands by the same author.

I too, of course, was surprised, and disappointed, by the results. I wasn't surprised that he found variation from sample to sample, but I was surprised at the overall low performance.

I always tell people that you pay for the specified performance, and you should get that...but that does not mean the certain samples won't exceed specifications. And who is going to complain if they get the "cherry" in the batch. At the same time, you can't complain if you don't get the cherry...as long as your sample preforms up to specifications. That kind of variation has been my experience of all the top brands over 20 years and more of testing. I expect that kind of variation.

And, since the low performance in the test is NOT my experience of Diascopes, and I do look through a lot of them in the course of my work, I'd like to see what kind of results he gets with other brands.

Finally, let me say that we do take all such reports from the field seriously, and review them, and, when they prove to have good basis in reality, as they rarely do, we take appropriate action.

S. Ingraham
Click to expand...

Nev
 
Looking for information (for non-astronomers) to use a USAF 1951 resolution chart, resulting in arc seconds of resolution, and relevance for a Zeiss 65A/zoom.

Mike
 
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