Are ZM Lenses light tight?

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thrice

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An odd question as obviously lenses aren't light tight, they pass light through them.

What I am asking, is does light leak through the barrel?

I have been having some issues with my 25mm ZM Biogon. For the record I know what I'm doing, and I have plenty of other lenses for reference, including 18mm ZM, 35mm ZM, 50mm ZM, 35mm lux asph, 90mm elmarit, 50mm color-skopar and 50mm nokton. As far as my testing goes this problem only occurs with my 25mm Biogon, and to a lesser extent my 50mm C-Sonnar.

Here is what I'm seeing, this is with a 12s exposure using an ND1.8 filter:
ZMFlares.jpg


It occurs regardless of aperture, ISO, white balance, using the hood or not, and even occurs with the lens cap on:
25BiogonFLARE.jpg


For comparison sake, here is the ZM C-Sonnar, followed by the 90mm Elmarit-M, with the same filter and at the same aperture as the first shot:
ZMFlares-2.jpg

Excuse the flare on the elmarit shot, the sun popped out and shone straight into the lens.
ZMFlares-3.jpg


Now some might be asking yes but why are you shooting with an ND filter? Well, the problem is I'm going to be shooting a lot of waterfalls in the coming months, using ND filters, and this is a deal-breaker for me.
If a lens cannot maintain light-tightness through it's barrell or flange for more than say, 4 seconds under moderate sunlight (these shots taken early morning through cloud except for the elmarit picture) then they're pretty bloody useless to me. Zeiss seem to think the problem is reflections on the inside of the M9 body, odd when it occurs with a lens-cap on but not with any other lenses. It is not an isolated incident, it occurred throughout the day when I was shooting long exposures using an ND and also occurs when using an IR filter (due to the length of exposures)

I suggest others test this as well, simply take your camera outside - it would be great if you could test this with a 25mm Biogon for my peace of mind that good copies exist - leave the lens cap on and select an 8s exposure, click the shutter and wait, then examine the resulting shot and please post it if possible, that way we can determine if I'm bonkers or if Zeiss have a QC problem.

I should mention that Tony at Popflash has been exceedingly helpful and patient with me in trying to diagnose and resolve this issue. I hope it's isolated to just me 🙂
 
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Either your camera has a leak or you had some exceedingly bad luck.

I had 7 Zeiss ZM lenses: never a problem of any kind.

Best, Horea
 
Cheers, as per my post this doesn't occur with other lenses (except the c-sonnar - but far less-so in that case) so it is not a light leak in the body. I'm likely to put it down to bad luck and hope a repair/replacement solves my issue.
 
I think I would try some shots without the ND filter. I have a feeling it might be reflecting light back into the lens. Is the ND filter coated/multicoated? I sincerely doubt that the lens barrel is leaking light. Instead, it could be a case of a borderline flare situation combined with a problem being caused by the filter.
 
If it's leaking light, I suspect it's coming in from the lens mount.

Maybe you could try some tape around the most likely suspect area: where the lens mounts to the camera, and try it. If the leak is gone, you've isolated the problem.
 
thrice said:
It occurs regardless of aperture, ISO, white balance, using the hood or not, and even occurs with the lens cap on:
25BiogonFLARE.jpg
Click to expand...

Rob-F said:
I think I would try some shots without the ND filter. I have a feeling it might be reflecting light back into the lens. Is the ND filter coated/multicoated? I sincerely doubt that the lens barrel is leaking light. Instead, it could be a case of a borderline flare situation combined with a problem being caused by the filter.
Click to expand...

Hi Rob, thanks for the suggestion, alas as per my quoted picture, the filter is irrelevant.

Brian Sweeney said:
If it's leaking light, I suspect it's coming in from the lens mount.

Maybe you could try some tape around the most likely suspect area: where the lens mounts to the camera, and try it. If the leak is gone, you've isolated the problem.
Click to expand...

Good suggestion Brian, I'll test it with my 50mm C-Sonnar, as my 25mm Biogon is boxed up ready to be mailed to Popflash 🙂
 
Rob-F said:
Yeah, I see what you mean. Is there a screw missing somewhere on the lens barrel? That might account for a light leak.
Click to expand...
The lens was babied (as is all my equipment) and I would be extremely surprised if any components had shifted or come loose during the life of the lens. But I'm sure Tony Rose will tell me if something is amiss!

I have sent the lens back to Popflash who are solving the problem for me, can't say how much I appreciate their help and I hope Zeiss look after them as well as they've looked after me.

I believe light was entering the barrel or the lens mount. Because no other lens shows this kind of corner brightening, and it occurs with a push-on lenscap on. That rules out the body, and it rules out flare from filters etc.

Double Negative said:
Or shoot in the dark.
Click to expand...
I did try this with identical camera settings, and no flare occurred.
 
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Double Negative said:
Okay, so it's definitely a light-induced issue. Have you tried wrapping JUST the lens (not the mount area) to see if it's actually coming from the lens barrel?

I find it very hard to believe it's a lens barrel leak. For one thing, light on its own travels in a straight line. It doesn't go around corners (unless reflected). You'd need quite a hole in the side of your lens to let in this much light...
Click to expand...

It's a 12s exposure in those examples, with an ND1.8 filter, it has occurred noticeably on 8s and 4s exposures as well though, to a lesser degree. My lenses are silver, so perhaps that has an influence.

back alley said:
how long have you been using this lens?
and it's only recently that this started to happen?
did you drop the lens or bang it?
Click to expand...

Since October 09.

It's only recently that I've shot in reasonable light with longer than 1s exposure, so I'm not sure.

The lens was treated impeccably and hasn't had any impact at all, it is completely mint mechanically (apparently) and cosmetically.

Since the same effect occurs very slightly with my 50 C-Sonnar (silver as well) I will try wrapping it tomorrow morning and shooting similarly to see if it eliminates the issue.
 
maybe it's a stupid thing. But could it be that the Viewfinder/rangefinder system has a light leak.
The leak shows up at the bottom of your pics, but if i'm correct this should be the top of the negative when it's in the camera. And with all the prisms and mirror in there it would be possible for the light to get reflected from the viewfinder into the camera.
Did you try making a exposure with the viewfinder/rangefinder covered.
It's just an idea, don't now if it is a stupid one. But it might be worth trying out.
 
HoodedOne could be right, because I've heard of some cameras having metering problems when using an external finder.

But then Double Negative asked a valid question about the isolated chamber of the RF.

At first I suspected maybe a leak near the door because the barrel and mount are usually pretty solid. And it seems weird that the light would leave a small piece straight across unaffected at the bottom. A leak from the lens would be covering that quarter completely(??).

But then thrice mentioned that the occurrence was with the 25mm. Or maybe because the use of an external finder, the face is not blocking most of the camera body's backside with the 25 + viewfinder, whereas using a 50 or 90 would have you peeping through the rangefinder and covering the backside of the camera. I probably would check the camera body again, and test with the rangefinder covered...
 
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Ok I taped and tested my C-Sonnar.

With just the barrel taped (not all the way to the mount) I still get the flare, when taping all the way down to wrap around the lens mount I get no flare.

So this is a case of flange construction quality. Either the lens isn't clamping to the body tightly enough, or the flange is not uniformly flat.

Before those who don't like to read the thread come charging in and say it's my camera body, it isn't, it only happens with my 25mm biogon and to a much lesser extent my 50mm C-Sonnar, out of my total of 7 M mount lenses and one LTM lens on an adapter.

without tape:
ZMFlares-2-2.jpg


taken immediately after with tape:
ZMFlares-4.jpg
 
That is a convincing test! I've never had this happen to any of my lenses, but have not taken such long exposures with them. I'll be surprised if my vintage collapsible lenses do not leak a bit like this. Now I'm going to have to test them with the lens cap on and find out.
 
It's not something that will show up in most general usage. So little that I'm not concerned about it on my 50 C-Sonnar at all, because I'll never shoot in these real-world conditions.

However, with my 25mm Biogon, and wanting to use smallish apertures and ND or IR filters then this starts to become a real problem.
 
ferider said:
How are your lenses coded ?

Also, does the behavior change at infinity focus (vs. close up) ?
Click to expand...

Please explain the logic of these questions when the light is leaking through the lens mount?

The 25 Biogon is coded as a 24 elmarit asph, and the 50 C-Sonnar is coded as a 50 lux asph.

The behaviour does not change with focus distance. What was your theory?
 
1.) I was wondering if you might be using a paper-stripe-based coding kit, on your Zeiss lenses only; the paper stripe might raise the lens mount just a little.

2.) From the location of the leak it happens somewhere between 12 and 3 o'clock, when looking at the camera from the front. Which happens to be where the mount flange has the RF coupling indentation. For infinity focus this "dent" gets covered more by the lens' coupling cam, and the leak should get darker, if this is where the light goes through.

Just 2 ideas ...

Roland.
 
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