Curtain or shutter problem?

TomR55 · Jun 20, 2023

I have a Leica M4-P body that began to "skip frames" (meaning that on a roll of 36 exposures, two or three frames would be completely blank). This problem arose after a CLA. In response, the technician who performed the CLA replaced the small curtain. Now, I have two (or more) frames partially-exposed on a roll of 36 exposures. I am certainly not a technician. Is it possible that what I am seeing is NOT a curtain problem, but a shutter problem? And, if so, how difficult/expensive is it to replace a shutter for this camera?

Tel · Jun 20, 2023

I'm not specifically familiar with Leicas, but nearly all curtain-type focal plane shutters operate similarly. First, the curtains are the shutter. In a leaf-shutter mechanism you have a set of metal leaves that open and close to allow light to past through. In a curtain shutter mechanism you have two shutter curtains that travel, one behind the other, across the gate. There's a delay mechanism (typically a set of gears) that causes the second curtain to stay open after the first curtain has opened, exposing the film to light for a specific amount of time before the second curtain closes. What's wrong with your camera might be a timing error on the second curtain; it might be closing too early or not opening at all, i.e., not being delayed after the first curtain has opened but travelling across the gate with it rather than after it. A partial-exposure problem would be consistent with such a timing error but could also be due to incorrect tensioning of the take-up rollers: if the first curtain is travelling too slowly or not completing its travel at all and the second curtain is catching up to it too soon.

Edit: so the problem is likely not one that will be solved by replacing the curtains themselves, but by finding some sort of malfunction in the mechanisms that drive the curtains and fixing that.

TomR55 · Jun 20, 2023

Tel said:
I'm not specifically familiar with Leicas, but nearly all curtain-type focal plane shutters operate similarly. First, the curtains are the shutter. In a leaf-shutter mechanism you have a set of metal leaves that open and close to allow light to past through. In a curtain shutter mechanism you have two shutter curtains that travel, one behind the other, across the gate. There's a delay mechanism (typically a set of gears) that causes the second curtain to stay open after the first curtain has opened, exposing the film to light for a specific amount of time before the second curtain closes. What's wrong with your camera might be a timing error on the second curtain; it might be closing too early or not opening at all, i.e., not being delayed after the first curtain has opened but travelling across the gate with it rather than after it. A partial-exposure problem would be consistent with such a timing error but could also be due to incorrect tensioning of the take-up rollers: if the first curtain is travelling too slowly or not completing its travel at all and the second curtain is catching up to it too soon.

Edit: so the problem is likely not one that will be solved by replacing the curtains themselves, but by finding some sort of malfunction in the mechanisms that drive the curtains and fixing that.

Thank you for your coherent and extremely helpful response. Assuming the least problematic case, i.e., a timing error, then this problem is correctable by a skilled technician and does not (necessarily) require a major investment in additional parts--if I understand you correctly.

Tel · Jun 20, 2023

TomR55 said:
Thank you for your coherent and extremely helpful response. Assuming the least problematic case, i.e., a timing error, then this problem is correctable by a skilled technician and does not (necessarily) require a major investment in additional parts--if I understand you correctly.

In all probability, yes. It does, of course, depend on the source of the timing and/or tensioning error. Could be a broken gear or a bad tensioning spring, though, which could be an expensive fix. As I say, I don't own any Leicas, so I don't know how scarce parts may be these days. I expect someone on Photrio will have a good idea of the state of things vis-a-vis spares.

TomR55 · Jun 20, 2023

Tel said:
In all probability, yes. It does, of course, depend on the source of the timing and/or tensioning error. Could be a broken gear or a bad tensioning spring, though, which could be an expensive fix. As I say, I don't own any Leicas, so I don't know how scarce parts may be these days. I expect someone on Photrio will have a good idea of the state of things vis-a-vis spares.

Thank you very much for the follow-up: Perhaps the best place to begin is with the person who performed the original CLA, and to continue monitoring this thread.

ic-racer · Jun 20, 2023

Would need to know which shutter speeds are affected and the curtain transit time of each curtain (measured under whatever conditions one can create to allow the shutter to open to get the measurement.) Should be about 14ms.

You can build an inexpensive shutter tester to get this information.

Build a shutter tester for Focal Plane shutters - Cheap, Easy & it Works

Tel · Jun 20, 2023

TomR55 said:
Thank you very much for the follow-up: Perhaps the best place to begin is with the person who performed the original CLA, and to continue monitoring this thread.

I'm guessing you don't want to try fixing it yourself; so sending it back to the repair person who did the CLA is a good move, as long as you're not in a great hurry to get it working. You might also want to ask Leica owners in this group who they use for repair work.

Sirius Glass · Jun 20, 2023

The repair person should make it right at no charge to you. Otherwise ask for a full refund, that should motivate him or her.

awty · Jun 20, 2023

Are you sure the technician is competent? They are not that complicated.
Without film in it or a lens on, you can open the back point to a light source and see if the curtains are operating.

TomR55 · Jun 20, 2023

ic-racer said:
Would need to know which shutter speeds are affected and the curtain transit time of each curtain (measured under whatever conditions one can create to allow the shutter to open to get the measurement.) Should be about 14ms.

You can build an inexpensive shutter tester to get this information.

Build a shutter tester for Focal Plane shutters - Cheap, Easy & it Works

Interesting point. The problem first arose at 1/1000 and 1/500, intermittently ... usually after a flurry of continuous shooting. Now it might be relevant to your question to note that in the first (original) case the impacted frames were completely unexposed---i.e., we saw no vestiges of the original scene on the negative. I had someone replace the short curtain and this appeared, at first, to have rectified the problem. A few days into continuous use, I see a slightly different problem: incomplete rendering, meaning that a small, normally exposed fragment of the scene is visible on the affected negatives--about three per thirty-six. These frames were exposed at 1/500 and 1/250 as opposed to 1/1000 as in the original case.

An additional piece of information: while shooting I notice a "thud" (a louder than usual noise) when the shutter closes, and I believe that this occurred on the affected frames. I'm not certain, but it almost appears that I can feel internal impact that I do not generally notice with these cameras (and yes, I used Leica M bodies for about 30 years--for what that's worth).

Thank you for your follow up; I don't know if these responses are helpful, but I am welcome to hear any responses ...

Tel · Jun 20, 2023

A thud can't be normal. Could be the metal splines on the free ends of the curtains colliding with each other.

I'm only familiar with curtain shutters in the Minolta 35's and Nikon S's. But I've experienced the incomplete exposure thing in a couple of the Minoltas. In both cases it was insufficient tension on the takeup roller of the first curtain, meaning that it hadn't cleared the gate before the second curtain caught up to it. I don't recall if it made a noise but I do recall what the negs looked like: about 1/3 of the frame had been exposed and the rest was blank.

Sirius Glass · Jun 20, 2023

TomR55 said:
Interesting point. The problem first arose at 1/1000 and 1/500, intermittently ... usually after a flurry of continuous shooting. Now it might be relevant to your question to note that in the first (original) case the impacted frames were completely unexposed---i.e., we saw no vestiges of the original scene on the negative. I had someone replace the short curtain and this appeared, at first, to have rectified the problem. A few days into continuous use, I see a slightly different problem: incomplete rendering, meaning that a small, normally exposed fragment of the scene is visible on the affected negatives--about three per thirty-six. These frames were exposed at 1/500 and 1/250 as opposed to 1/1000 as in the original case.

An additional piece of information: while shooting I notice a "thud" (a louder than usual noise) when the shutter closes, and I believe that this occurred on the affected frames. I'm not certain, but it almost appears that I can feel internal impact that I do not generally notice with these cameras (and yes, I used Leica M bodies for about 30 years--for what that's worth).

Thank you for your follow up; I don't know if these responses are helpful, but I am welcome to hear any responses ...

Tel said:
A thud can't be normal. Could be the metal splines on the free ends of the curtains colliding with each other.

I'm only familiar with curtain shutters in the Minolta 35's and Nikon S's. But I've experienced the incomplete exposure thing in a couple of the Minoltas. In both cases it was insufficient tension on the takeup roller of the first curtain, meaning that it hadn't cleared the gate before the second curtain caught up to it. I don't recall if it made a noise but I do recall what the negs looked like: about 1/3 of the frame had been exposed and the rest was blank.

The Thud could mean that something was not properly fastened. A trip back to the repair person should be your next action.

TomR55 · Jun 22, 2023

A big thank you for the responses to my initial inquiry. I believe the consensus opinion is send it back for service and that's what I have done today. I'm hopeful that it's a minor adjustment, but time will tell ...

Curtain or shutter problem?

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