Just Purchased NIB 85mm Zeiss for $1300 (1 Viewer)

Leif · Jul 1, 2004

galt_57 said:
I would be interested to hear how many people star test their scopes and what percentage find problems. Is it possible to e-mail a photo of a star test to a mfg's customer support?

I star tested my Leica APO 77 with the zoom at 60x. It is correctly collimated, has no noticeable astigmatism but shows some spherical aberration as the diffraction rings are noticeably brighter and better defined on one side of focus than the other.

I doubt I would have star tested it if I had not started using it for wide field astronomy with a 20x eyepiece.

scampo · Jul 1, 2004

I shall test mine the next clear night we have. Fascinating stuff - but perhaps entirely irrelevant to its use in birding. We'll see!

(-:

Leif · Jul 1, 2004

scampo said:
I shall test mine the next clear night we have. Fascinating stuff - but perhaps entirely irrelevant to its use in birding. We'll see!

(-:

As someone else said, I wonder how much it matters if it has a bit of spherical aberration? What effect would that have on the image at typical birding magnifications i.e. <40x?

I am not surprised my scope would not match a Takahashi refractor. I seem to recall that in the UK a 3" Tak would be £1000 for an optical tube assembly only i.e. no focusser and no erecting prisms.

Jay Turberville · Jul 1, 2004

scampo said:
I shall test mine the next clear night we have. Fascinating stuff - but perhaps entirely irrelevant to its use in birding. We'll see!

It should be very relavent. Such a test tells you something about how closely the optic is approaching its design goals. We had a thread here recently where it was explained that a tested scope showed some flaw (astigmatism I think) and many people had judged (correctly) the scope as not having as good an image as others. Of course, this was attributed to the model and not the particular sample. The fellow posting loosended the objective mount and then retightened it and the scope's image improved significantly. Apparently tension in the mounting can cause distortions in the optcs.

henry link · Jul 1, 2004

scampo said:
I shall test mine the next clear night we have. Fascinating stuff - but perhaps entirely irrelevant to its use in birding. We'll see!

(-:

I think it's relevant in birding. You would probably notice that something is wrong with this scope I've been evaluating by just looking through it, even at 30X, but not everybody would. Even after noticing something is wrong you still wouldn't know the source of the problem. Is it a defect, or combination of defects in the sample or a design flaw?

The beauty of star testing, once you've got the hang of it, is that it can tell you not only whether something is wrong, but exactly what that something is and how bad it is.

Leif · Jul 1, 2004

Jay Turberville said:
It should be very relavent. Such a test tells you something about how closely the optic is approaching its design goals. We had a thread here recently where it was explained that a tested scope showed some flaw (astigmatism I think) and many people had judged (correctly) the scope as not having as good an image as others. Of course, this was attributed to the model and not the particular sample. The fellow posting loosended the objective mount and then retightened it and the scope's image improved significantly. Apparently tension in the mounting can cause distortions in the optcs.

Obviously no-one is saying that the image is independent of the optical quality when used for birding. My query though is what sort of level of aberration is discernable and more to the point intrusive when using the scope at 20x, 30 and 40x. (Maybe that is also Steve's point, but I won;t put words into his mouth.)

For example, does a 'slight' (hardly a quantitative measure) oval shape to the diffraction rings mean one should not use the scope for anything other than hammering nails into wood, or does it have to be marked. When this person induced astigmatism into the objective, and produced noticeable image degradation, what sort of distortion in the difffraction rings did this create? I could ask similar questions about the concentricity, and the difference in intensity either side of focus.

Yes I suppose I could get a book, but that would probably just tell me how to translate a diffraction ring into a wave error. Would 1/4 wave spherical aberration be perceptible and intrusive at 30x?

As it is my Leica APO 77 produces marvelous images - to my eyes - at 32x despite having some spherical aberration. (I don't know what wave error. Maybe Leica have maximum allowed tolerances?)

scampo · Jul 1, 2004

You're intriguing me more and more. I'll report back after I search for the thread for the technique. I have to say that of the three scopes of which I've had good experience I have no complaints whatever optically when they're used for birding. They're all still under warranty, though, so any faults and they'll be winging their way back to the manufacturer!

henry link · Jul 1, 2004

Leif said:
As it is my Leica APO 77 produces marvelous images - to my eyes - at 32x despite having some spherical aberration. (I don't know what wave error. Maybe Leica have maximum allowed tolerances?)

Leif,

I wouldn't worry too much about your Leica. Your description of your star test sounds just like what one wants to see in a short focal length refractor. Some spherical aberration is to be expected. If you saw very strong inner rings on one side of focus and only one bright outer ring with extremely weak or no inner rings on the other side that would probably mean too much SA for a good image even at 32X.

On the other hand it doesn't take very much astigmatism or collimation error to compromise the image and those things shouldn't be present at all if the scope has been made properly. BTW one possible source of astigmatism is your own eye. If you see an oval diffraction pattern you should rotate your head around the eyepiece. If the oval doesn't rotate with you the problem is in the scope.

Henry

kabsetz · Jul 3, 2004

Star testing is not specifically relevant to birding, but rather, it is relevant for anyone who wishes to determine whether or not a certain scope approaches or falls short of what can be achieved with that size aperture. Therefore, it is very useful to birders, if you get the distinction I'm after here. For birders, usually the fastest and most reliable way to determine a scope's performance is to set it up against a known reference, which needs to be a scope that you know has performed excellently in the field. As sample-to-sample variations are a significant factor here (as can be seen from posts in this discussion and in the wide variance of opinion if you read more than just one test report), it is not enough to have as a reference a known brand or model, but a known specific unit. Star tests, however, are indispensable if you have no such reference at hand, although it is not a trivial matter to accumulate enough experience to know what is good, what is mediocre and what is unacceptable - especially when it comes to birding optics where, unfortunately, manufacturing standards are not nearly as strict as we ought to hope for.

A very interesting (at least to me) finding I have made while star-testing birding optics has been that those units which IN FOCUS show the faintest and most symmetrical first diffraction ring around the airy disc perform significantly better than less well corrected scopes when there is thermal disturbance (shimmer, heat haze) in the air. Spherical aberration as such has not been a severe problem in most of the scopes I have tested, but there has been plenty of miscollimation, astigmatism, some pinched optics, poorly ground roof prisms, varying amounts of chromatic aberration within a single brand and model etc.

If more birders would begin to star test their scopes, eventually the manufacturers would probably be forced to improve their production standards, but we would also get higher pricing in the bargain, retailers would go insane with the demands of discriminating buyers, and an increasing number of birders would be chronically unhappy with the optics they use day in and day out.

So, Henry is doing everyone both a great service and a disservice by promoting the star test. If you want to learn more about star testing, buy or borrow Suiter's book "Star testing astronomical telescopes". Also, if my memory serves me right, on Cloudy Nights astronomy web pages there was an article by Thomas Back which had a brief intro to star testing. As far as artificial stars are concerned, on a sunny day out in the field you can find a glimmer of sun reflected from a dewdrop, chromed something, distant lampposts etc. which work quite fine.

galt_57 · Jul 3, 2004

kabsetz said:
So, Henry is doing everyone both a great service and a disservice by promoting the star test.

Leaves me wondering how many scopes (%) would fail the test.

Leif · Jul 3, 2004

henry link said:
Leif,

I wouldn't worry too much about your Leica. Your description of your star test sounds just like what one wants to see in a short focal length refractor. Some spherical aberration is to be expected. If you saw very strong inner rings on one side of focus and only one bright outer ring with extremely weak or no inner rings on the other side that would probably mean too much SA for a good image even at 32X.

On the other hand it doesn't take very much astigmatism or collimation error to compromise the image and those things shouldn't be present at all if the scope has been made properly. BTW one possible source of astigmatism is your own eye. If you see an oval diffraction pattern you should rotate your head around the eyepiece. If the oval doesn't rotate with you the problem is in the scope.

Henry

Henry. Thanks. On one side of focus I see numerous bright well defined circular rings of roughly equal intensity. On the other side they are similar but fainter and less well defined. Unfortunately there is not much focus travel on that side of focus.

I think I will get the book by Suiter. BTW I recall that the APM site has lots of star test examples.

I wonder if manufacturers would respond were a user to buy a scope that gave a poor star test?

henry link · Jul 3, 2004

Leif said:
I wonder if manufacturers would respond were a user to buy a scope that gave a poor star test?

My friend with the defective Zeiss scope is about to find out what Zeiss will do. He is returning the scope with a note describing the defects seen in the star test. I don't think he will have a problem since his scope is really pretty bad. The star test was mainly useful to determine why the image is so poor.

Jay Turberville · Jul 3, 2004

I attemped a daylight star test today but did so far too late in the morning. The desert floor was already heating up and the atmospheric disturbance was severe. But I did snap this picture of the specular highlight on a 1" ball bearing at a distance of about 100 meters. The scope was at 60x and the equivalent focal length was around 5000mm.

As you can see, when the air turns a bright spot into such a distorted flare, there is no hope of getting sharp photographs at this kind of distance and magnification if the air isn't fairly still.

BTW, the image was purposely underexposed so the flare would be better exposed. I adjusted the curves in Photshop so that the bearing could be seen.

galt_57 · Jul 4, 2004

Leif said:
Unfortunately there is not much focus travel on that side of focus.

Maybe this should indeed be the "ball bearing test" since, as you say, you may not be able to defocus a star on the far side(?)

A quick web search on "star test" yields a lot of writeups on the procedure.

Dave

henry link · Jul 4, 2004

Jay Turberville said:
As you can see, when the air turns a bright spot into such a distorted flare, there is no hope of getting sharp photographs at this kind of distance and magnification if the air isn't fairly still.

Jay,

The advantage here is high humidity and grass lawns. Keeps the air reasonably steady. Among my favorite targets are the porcelain insulators on electric lines since they are above the worst ground level instability.

Another easy artificial star can be made by punching very tiny holes in aluminium foil and placing it over a flash light lens or a light bulb. Good for cloudy days (or nights) or even indoors with no worries about air stability.This has worked for me at distances as close as 10m (the holes must be very tiny). This is too close to evaluate aberrations accurately but will show defects like pinched or uncollimated optics and astigmatism.

Henry

galt_57 · Jul 5, 2004

Well I made an attempt but can't see rings. Instead I seem to see a reflection of the defects within my own eye. Maybe my eyes aren't good enough anymore.

henry link · Jul 5, 2004

galt_57 said:
Well I made an attempt but can't see rings. Instead I seem to see a reflection of the defects within my own eye. Maybe my eyes aren't good enough anymore.

Dave, Try looking at the star in focus first. Make sure it"s centered in the field. At 60X the airy disc will be small so it could be difficult to tell whether it is perfectly round. It should be surrounded by a faint ring.

Now move slowly out of focus. The rings are the brightest and easiest to see when there are only about three to five. As you move farther out of focus the number of rings increases but they become fainter until you can't see them anymore. Now try the same thing on the other side of focus. They may be visible on one side of focus, but not the other.

BTW if you are using a real star it needs to be high up in the sky away from the horizon and the air needs to be steady. Hope that helps. Henry

Merv Goddard · Jul 5, 2004

Stay-on-cases my arm!!!

mickporter said:
Well done mate, and welcome to the world of Zeiss scoping..... You will not be dissapointed....... its a fantastic scope, made by an excellent company.

My only bugbear and its well documented is the crap objective lens cap. Would have hoped for something better there..... Am also still waiting for them to produce a stay on case that actually fits and stays on. At the moment I am advertising Opticron on my scope!!!! Hint hint to Zeiss spies!!!!

G'day Mick. As I'm only a fledgling spotter I'm buying 'Prudently' at the moment.(I'm actually a tight git!) I recently purchased an Acuter pro 100 and have a similar problem with my SOC. Its like a bag of ----. Advertised as a SOC you would think it would have an incision so you can attach it to your tripod or hide clamp. No such thing so I'm thinking of trying the Opticron ES 100 SOC as they are, to within 2cm's, the same size. Its whether the Tripod incision and focus wheel line up. Like you. I hope that an Acuter spy is a regular 'user' and can actually supply a proper SOC.

galt_57 · Jul 7, 2004

Oddly enough I've come across another Zeiss 85 message regarding a failed star test. In a followup e-mail he further commented that he checked two Zeiss scopes and they were both the same, so he bought a Leica instead.

--- In [email protected], "paschr9" <[email protected]...> wrote:
>
> Greetings -
>
> I am new to this list but have been active in amateur astronomy for
> quite some time. I have had an interest in acquiring a spotting
> scope for some time as a possible replacement for my Tele Vue 85 -- I
> thought it would be nice to have a lighter "quick look" scope for
> daytime and nighttime use, as long as the trade off in optical
> quality wasn't too severe.
>
> Based on comments here and elsewhere I ordered a new Zeiss Diascope
> 85 + zoom, which arrived today. It appeared to have some problems
> somewhere along the line as the lens cap was off and loose in the box
> and the lens cap itself was no longer functional (one of the gripping
> mechanisms was broken off).
>
> Well, I tried it tonight on Saturn and Jupiter and I think I must
> have one that is defective. The images were quite poor, with no real
> sharp focus at the maximum zoom magnification (or any other
> magnification). Worse still both Jupiter and Saturn were lost in a
> hazy glow; my TV-85 set up right next to the Zeiss was as sharp as a
> tack.
>
> I did a star test (as amateur astronomers like to do) and it struck
> me as quite unusual -- in focus was pretty sharp, but outside of
> focus the image was so mushy that no rings were detectable.
>
> I would have expected that Saturn would be quite sharp, so I'm
> assuming I just got a lemon. FWIW I've owned several Tele Vues and
> all have been superb optically. I bought mine from a very good
> dealer and I'm sure they'll work this out, but it is a bit
> frustrating. I think I will try a replacement, but I might just bail
> out and stick with the known (albeit heavier) quantity.
>
> Any comments on what I should expect in terms of Saturn images would
> be helpful, as would be any perspective on how a "good" Zeiss looks
> in a star test.
>
> Best regards,
>
> Paul Schroeder

Leif · Jul 7, 2004

galt_57 said:
Oddly enough I've come across another Zeiss 85 message regarding a failed star test. In a followup e-mail he further commented that he checked two Zeiss scopes and they were both the same, so he bought a Leica instead.

Given that many BF users own scopes, we thus have the means to do an online scope sample variation survey. In other words, we all post a brief description of how our scope star tests at ~60x, not forgetting scope details. No doubt, given the previous enthusiasm for my suggestions, noone will be interested ...

Just Purchased NIB 85mm Zeiss for $1300 (1 Viewer)

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