Zeiss scope repair (1 Viewer)

I am happy to report that the replacement scope for my friend’s Zeiss 85mm Diascope has arrived and it is completely free of the defects the first sample had. I measured it’s resolution to be 1.6 arc seconds, a good figure for a birding scope of this aperture, but not as close to diffraction limited as the 1.9 arc secconds I measured recently on a Swaro ATS-65HD.

The scope star tested fine in terms of defects, no sign of astigmatism, miscollimation or pinched optics. There were completely round, very strong diffraction rings on one side of focus and very weak ones (except for one very strong outer ring) on the other side, indicating a bit more spherical aberration than I saw in the Swaro 65, which is really to be expected from the lower focal ratio objective. Most importantly the image quality is exactly what it should be in this scope, quite sharp and high contrast at lower magnifications with just the relatively small amount of deterioration at high magnification that is to be expected from the SA seen in the star test and the measured resolution

I can’t think of a better example than this of why new scope buyers should immediately do the simple 60X star test. My friend was ready to accept a seriously defective scope simply because he didn’t have the optics experience necessary to recognize a flawed scope image when he saw one. In fact, most birders don’t have that kind of experience with telescopes, so there could be quite a few dud scopes in use.

(Dave, if you see this I was able to read the tiny numbers on the $1 bill at 128’ through the replacement scope at 60X.)

Henry.

Good to hear that your friends scope has been sorted out, however I do not think that the star test will always tell you whether the scope is good or not.

Careful Henry.
I know that some birders do have experience and some knowledge on optics, certainly in the UK, with respect, I cannot comment on the US birders, so I hope that your comment was a little tongue in cheek.

henry link said:

I am happy to report that the replacement scope for my friend’s Zeiss 85mm Diascope has arrived and it is completely free of the defects the first sample had...

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Henry, I looked again at 128 feet in full sunshine but the smallest characters are not readable to me. Now what happened between the time the technician told your friend there was "nothing wrong" with the scope and the time they finally returned the scope?

Thanks,

Dave

galt_57 said:

Henry, I looked again at 128 feet in full sunshine but the smallest characters are not readable to me. Now what happened between the time the technician told your friend there was "nothing wrong" with the scope and the time they finally returned the scope?

Thanks,

Dave

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Dave,

Check the first entry in this thread. Zeiss agreed to replace the scope with a new one, in part because they have no repair facilities for Diascopes in the US. Judging from my experience it's a good idea to be sure your scope is defective and to know what's wrong with it before dealing with Zeiss (or probably anybody else). If you return it to them with a vague complaint you may just get the same phone call my friend got. Without a "reference" scope known to be good for comparison, it can be difficult to tell for sure whether the image in a scope is as good as can be expected for that type scope or poor enough to indicate defective optics.

Henry

henry link said:

Judging from my experience it's a good idea to be sure your scope is defective and to know what's wrong with it before dealing with Zeiss (or probably anybody else).

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I'm still unaware of any scopes in my area although I'm sure I could eventually track down an astronomy club. I would hope that Zeiss would keep a few known good scopes in stock for test purposes if they plan to support these in the US.

Dave
St. Louis

8/31 Update - They sent me a new scope body and returned my previous zoom eyepiece. Not sure if they determined my scope body had a detectable flaw or if this was simply a preemptive replacement.

(From Henry)
........Once again I would urge birders to learn how to test and evaluate your own scope, get a resolution chart, learn how to star test. Don’t assume a high status brand name guarantees a defect free scope, and don’t expect a defective scope you return to the manufacturer to receive some sort of high tech, sophisticated optical evaluation. It may just get a quick look from somebody who knows less about it's problems than you do.[/QUOTE]
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The above is an old note, but I just signed up a few days ago and it caught my eye. Some years ago I became interested in the Leica Televid Apo 77mm. I ordered three from different vendors intending to see if there were significant differences and retain the best for myself. My testing methods are similar to Henry's ie: I magnify the image and evaluate the intra/extra focal patterns as well as use test charts both magnified and at standard power.
Without going into too much detail, I ended up contacting a Leica factory technician and was told that the minimum spec. for these apo scopes was 1/2wave. I was quite surprised at this thinking that such an expensive scope would certainly be better than that. This indeed echoed what I had observed and estimated among the three samples.
One scope did indeed have about 1/2 wave s.a. - in the real world that meant that at 20x it looked about as good as the others but at 60x there was a noticeable softening of the image. The next was a little better but had some astigmatism. The third was close to 1/8 wave ! (Guess which one I kept . I fabricated several higher power eyepieces including a very high power eyepiece from an 2.5mm LV. I know that is pushing it even for a high quality apo spotting scope, but it performed quite well giving an almost perfect diffraction pattern. I could see Cassini's division on Saturn, split epsilon lyrae and spent many hours viewing things on good old Terra Firma.
Anyway, I guess the moral of the story is, as mentioned above, learn to evaluate the optics you buy, and you may end up with something exceptional as I did with that Leica scope or at least you won't get stuck with a lemon or wonder why it 'just isn't right' (A year later I sold it to a professional photographer on the East coast :egghead: minus the high power eyepieces) - Herb

p.s. : I could also tell you a few things about a Questar I once owned!

Thanks for the information, Herb. A 1/2 wave standard would certainly explain the sorry quality of the "average" specimen of birding scope. I've been looking for one of those 1/8 wave jems from Nikon, Swaro or Zeiss (now Kowa) since last summer. I haven't found one.

henry link said:

Thanks for the information, Herb. A 1/2 wave standard would certainly explain the sorry quality of the "average" specimen of birding scope. I've been looking for one of those 1/8 wave jems from Nikon, Swaro or Zeiss (now Kowa) since last summer. I haven't found one.

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What does Zeiss (now Kowa) mean, Henry? Have I missed some important news?

Steve,

Sorry for the lack of clarity. I only meant that I've recently added the new Kowas to my short list in searching for a cherry scope specimen. I have some design preferences but the brand is less important than the quality of the individual scope. I hear a new Leica 82mm is coming this spring which will add another scope to the list unless I find a 1/8 wave specimen before then.

Henry

Great insight. Thank you.
Would you have a link to good resolution chart?
I am using small print from across the room now. It does show he differences between optics but does not quantify them in a meaningful way such as lines per mm etc.

Thanks in advance
T

H2E said:

(From Henry)
........Once again I would urge birders to learn how to test and evaluate your own scope, get a resolution chart, learn how to star test. Don’t assume a high status brand name guarantees a defect free scope, and don’t expect a defective scope you return to the manufacturer to receive some sort of high tech, sophisticated optical evaluation. It may just get a quick look from somebody who knows less about it's problems than you do.

Click to expand...

[/QUOTE]

You can purchase a USAF 1951 test pattern printed on a plastic card from Edmund Optics (www.edmundoptics.com). The part number is U38-710. I think the price is up to $5 now. The printing is not very sharp but you can get an accurate resolution measurement if you place the card far enough away so that the smallest resolvable bars are in Group 2.

Thanks! I ordered 2 at $3 each +$10 shipping!!!!

For fun comparisons,
http://members.cox.net/lenstestr1/lenstest.htm
http://www.normankoren.com/Tutorials/MTF5.html#download
T