Are ZM Lenses light tight?

Ahh yes if I was using a paper coding solution that would certainly explain it. I just used a sharpie though, no paper.

I originally noticed the problem AT infinity 🙁 I'm hoping my new 25 Biogon will be perfect, I'll definitely post when it arrives and repeat the tests.
 
Hmm, sorry, just two long shots. Let us know if the new Biogon behaves better, and best of luck. Would be a deal breaker for me, too.
 
Yes, that was me. I tested all three ZM lenses and they all show the light leak. The 25 and 28 show the most and the 35 a little less. Also tested with a body cap and an Ultron 28/2 and it does not show a leak with any of those.

Here are some pics all taken at ISO 320 at 3s exposure in an M8 with a desk lamp shining right on the top of the lens mount about 2 inches away.

with body cap on
lenscap.jpg


Ultron 28/2
ultron28.jpg


Zeiss ZM 28
zm28.jpg


It's not quite as strong as if I try it with the sun, but still easily seen and reproduced.

-Thomas
 
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My C-Biogon has no issues either, just the 25mm Biogon and C-Sonnar. I imagine it's a clamping tightness or flange flatness variation problem.

Double Negative, it's a shame that your lenses have the potential to cause problems as well, bear in mind that my tests were done on an M9 and the corners would be much less affected on the M8.

At the end of the day this is something that will affect someone shooting with these faulty lenses for long exposures in sunlight (ie. with ND filters) or shooting IR on an unmodified M8/M9 requiring longer exposures.
 
I've found a way to solve the light leaks I have observed and have posted in detail on the GetDPi thread. In brief, the solution is to cover up a screw on the ZM lens mount that is opposite a screw on the mount on the camera. This eliminates the leak in my tests.

-Thomas
 
The screw that causes the problem is the one where the cutout for the focus following arm is.

Here is the screw on the lens (covered with a small piece of gaffers tape):
lensscrew.jpg


it happens to be opposite this screw on the mount on the camera body:
bodyscrew.jpg


So, by covering the screw on the lens I go from this (ZM 25mm, ISO 320, 4s):
zm25.jpg


to this (same exposure):
zm25withtape.jpg


-Thomas
 
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Thanks Thomas! You smart man you 🙂

At least now we know it's a design flaw, I think I've wasted mr Tony Rose's time by sending my 25mm ZM back to him 🙁 Zeiss should offer a replacement to owners of these lenses who find the issue a problem in their shooting.

I will fix my 50mm C-Sonnar myself, and probably cover the screw on my other ZM's to avoid the possibility of the problem coming up in future.
 
I'm on my way out to pick up some black silicone. I'll post results after it sets and I get to re-test my C-Sonnar.

Zeiss will undoubtedly say that they only guarantee flawless performance on ikon bodies. However, they should modify their compatibility to reflect that this issue can occur with some samples of the lenses with exposures longer than 4s in bright light.

Either way, I'm just glad there is a solution to the problem!

EDIT: returned with black silicone. I chose to cover up the screws on the M9 body instead, and then used a sharp plastic edge to get a flat finish while the silicone is still liquid. Any excess around the holes can been cleaned up with turps or (what I used) Eclipse E2. 😛 The silicone I usually buy comes in a toothpaste sized tube and has a conical applicator which I just snip the tip off so that it applies the smallest amount possible.

Now I just have to wait for it to set. If it doesn't help I'll try covering the screw on the lens as well.
 
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hmmm, taping the screw hole on the lens solves the problem, but taping the screw hole on the body doesn't. So it's a conjuction of the two but the fault remains with the ZM I think... have to do more testing.

I'm wondering how some people's lenses don't cause this problem, is it that they didn't test with direct enough light or long enough exposures? Or could Zeiss be aware of the problem and have changed screw locations silently?
 
Well, they did change the location of the screws some time ago and also introduced a shallow groove around the mount. This groove makes it easier for people to hand code the lenses but it also reduces the surface of the mount. It seems that the newer mounts are the ones having this problem. I think people with older lenses simply don't have the problem.

-Thomas
 
Ahh makes sense! What a shame. I wonder if there is a permanent solution, I'll try silicone on the lens again, I've filled the screw hole on the camera but that didn't help surprisingly.
 
Well, the M7 has six screws and none in the same position as the one that was giving the problem on the M8, so I think it has to be tested for various configurations of the M-mounts out there. My Hexar RF only has four screws, so the results would be different than both the M8 and M7.

Again. this is only a problem when shooting with IR or ND filters using long exposures in bright light. I wouldn't worry about it unless it actually shows up as a problem.

-Thomas
 
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