Leica 'M' Shutter Light Leaks AKA Shutter Opacity
Updated: Dec 17, 2022
What I'm about to share with you are some basic facts about the Leica 'M' shutter design and why in certain circumstances, you can and occasionally will get light leaks. This does not necessarily mean you have a 'faulty' camera. Believe it or not, this is simply a characteristic of the shutter design but it is one of the most frustrating faults for a camera engineer to fix, as a film test is almost always required at each attempt in order to confirm success.
The aim of this article is to inform you of some lesser understood technical aspects of your Leica camera. As an enthusiast or collector, there is an abundance of information about almost every aspect of Leica cameras and lenses online and in print, websites and in books and reviews but relatively little is written about the detailed mechanical aspects of these cameras. The basic principles are well understood but not the kind of details that the typical service engineer has to deal with. I am interested in how things work, or more to the point, why they don't and why Leica did things the way they did. I offer some of my thoughts to those who may be interested.
The Leica 'M' range was produced using modern manufacturing techniques but they had more in common with batch, hand built scientific equipment than their standardised mass produced cousins from Japan. More of a Morgan than a Porsche. This gave Leica manufacturing flexibility and the ability to make design improvements to internal parts on the fly. It also led to some creative, if not quaint solutions to problems. For example, there is a film door light seal that runs just under the top plate and fits into the hinge area at the back of the camera. If you look closely, you'll realise that it is just a strip of shutter curtain fabric which is glued to the top edge of the shell. I believe this solution used offcuts of material from the shutter making department that would otherwise go to waste. A mass produced camera may have had a slick, professionally designed part instead. Economies of scale would make it a cheap solution because although more expensive to make, it would be designed to simplify, thus speed-up the mass production process, reducing production costs.
The Leica 'M' range are on the whole excellently designed and superbly built. Providing your camera has been properly maintained, you shouldn't really have problems with light leaks. Leica state confidently in one of their service manuals, words to the affect of “Providing all light seals are correctly fitted, there will be no light leaks”. This is perfectly true with respect to the camera body but the shutter may be a different matter.
Shutter Light Leaks
If you ever experience light leaks, most likely, it'll be shutter related. The usual problem we see, is a diffuse overexposed looking band, running horizontally about a third of the way down from the top of the developed image. See the image below. Because the image is inverted in the camera, the band is actually about a third of the way up from the bottom. The horizontal band isn't over exposure though, but a light leak that has worked its way under the edge of the shutter curtain. This problem is generally confirmed if the problem is constrained to the image only and not between the frames or below or above into the sprocket area. It may not happen all of the time, just an occasional but annoying thing. Sometimes the problem can appear quite randomly with some frames affected and others not, even if the the lighting conditions are the exactly the same.
Shutter Opacity I once heard the term 'film gate opacity' which referred to the ability of a camera shutter to block light between exposures. I'm going to borrow this term and simply refer to 'shutter opacity' meaning the same thing. Leaf shutters, like the ones you see on a Rolleiflex or Hasselblad are very effective at blocking light, because the shutter blades are very very closely interleaved there is very little chance of any light leakage therefore, they have a very high shutter opacity. Focal plane shutters such as the Leica shutter are much less effective. This lack of opacity has nothing to do with holes in the shutter curtains or light leaking through the fabric, although that wouldn't help, what I'm talking about is the overall effectiveness of the Leica shutter to block light between shots. The shutter curtains on a Leica aren't tightly fitted together like a leaf shutter. There are air gaps between them and the baffle - the black metal part you see if you remove the lens and is situated directly in front of the shutter.
Because shutter opacity is relatively low, it one would expect regular light leaks but in practice, it isn't usually a problem and the habits of the user plays a part in this. If you are a careful type of person who avoids changing lenses in bright light and judiciously uses lens caps or perhaps a case, chances are it has never happened to you at all. If like me, you lose lens caps within minutes and carry the camera around for extended periods with the aperture wide open, forgetting to shield the camera from bright light during lens changes, it may be a more common occurrence.
In an imaginary scenario, we might then see a question posted on a Leica forum about one of these light leaks from the shutter. It's a Leica right? Should this even happen? Careful people say things like “I've used a Leica M3 for 50 years and I've never heard of such a thing”. Therefore the camera must be faulty and you need to spend £££'s to get it fixed. I can think of one such occasion where one of our customers had occasional odd frames affected and had been convinced that his camera had a serious problem and I think we were the third repairer to take a look at his camera. The two previous repairers were unsuccessful and were derided but we couldn't find anything wrong with that particular camera either.
The previous repairers were obviously given a hard time because I could see that they had tried to bolster the original light seals in a vain attempt to fix the problem. If we left the camera without a lens in a bright place, a window ledge for example, some fogging would sometimes happen but our customer was adamant that being a Leica, this should never ever happen. With a lens on his camera, I could go out on a sunny day and shoot a roll of film (we did various film tests), with no problems found on a 36 exposure roll. I'm sure, with a lens attached, if the aperture set wide open and I left it in bright light for long enough, some light would eventually get through and this occasional phenomenon stressed him so much, he couldn't enjoy his camera. We did advise him and we fitted M6 baffle strips (more about that later), and eventually he was satisfied.
So, the focal plane shutter is less opaque than a leaf shutter because it consists of two independent fabric curtains that have to travel from one side of the film aperture to the other. The spring tension of the shutter curtain rollers is relatively low, so it is important that the curtains can complete this action smoothly, without any restriction. If you look at the image below, a simplified cross section, you will see that the shutter lies between the baffle and the film aperture of the camera body casting and as previously stated, the shutter operates within an air gap.
Because we know that light doesn't like to go around corners, conventional wisdom tells us that direct light can't get through the baffle onto the film and that any stray light that might eventually land on the film would have to bounce off the black shutter fabric and the matt black components before getting under the shutter and onto the film. The intensity of that stray light must be so low, compared to the intensity of light required to expose the film, it shouldn't cause any problems – right? Wrong. A digital camera sensor can be switched off between shots. Not so with photographic emulsion, which is permanently 'switched on', recording everything until it has been developed. Single photons won't expose your film but repeated exposure to single photons over time will eventually cause the silver halides to react and form metallic silver. It isn't the light intensity that is the issue. It is:
light intensity x time x ISO rating of the film.
When the Leica M3 was first introduced, the sensitivity, or ASA/ISO ratings of contemporary films were much lower than today. My personal favourite was Kodachrome II rated at only 25 ASA and that was in the early 1970's. Ektachrome was rated at 64ASA and I recall GAF 200 was considered pretty fast for slide film. In the 1950's many black & white films were around around the 32 ASA level. The light baffling was satisfactory at the time but even so, carrying the camera around on a bright sunny day without a lens cap, or changing lenses in sunlight would still cause occasional fogging of some shots.
Albedo I say! All of the components inside the camera are painted with so called matt black paint and the shutter fabric is black. Albedo is the measure of how much a surface can reflect solar radiation on a scale of 0 to 1. Most modern matt black paints don't perform very well at all, especially after it has been handled because the surface becomes burnished and more reflective. Even the black silk fabric of the curtains is quite reflective. White paper may have an albedo of between 0.7 and 0.8, shutter curtains have an albedo in the region of 0.1 and 0.15 and the matt black paint 0.05 to 0.1. It doesn't sound a lot but without a physical barrier, enough light will bounce around and eventually reach the film. Wide angle lenses can make things worse because they introduce light at quite acute angles, reducing the effectiveness of the baffle as a shadow mask.
The Leica 'Plush' strip
In order to mitigate this effect, Leica introduced baffle strips or 'plush strips' that were glued to the inside of the baffles, starting with some of the later LTM models and on the M3 and subsequent cameras. The plush strips are actually made from simple strips of velvet, allowing the shutter curtains to brush past them with the minimum of friction. This doesn't afford complete light sealing but the pile of the velvet is quite effective at creating an additional barrier. Velvet pile also absorbs light quite well, that is why it can make an excellent black backdrop. The first shutter curtain however, is set slightly further back towards the film than the second, so the plush strips should theoretically work better if the shutter is left uncocked between shots. When cocked, the gap between the plush strip and the first curtain is just a little wider. You can see for yourself on the following picture. The camera was a M3DS received in quite poor condition, but you can see that the shutter curtain on the right is set slightly further back than the curtain on the left. It may seem insignificant but the velvet pile is quite short and this can make a difference.
One fault that many Leica engineers overlook are curled edges of the shutter curtain/s. If the curl is facing away from the plush strips, light can get under the edge of the curtain much more easily and can lead to annoying intermittent problems. The user might find that some shots are fine and others fogged even when light conditions are the same. Here is a common but frustrating scenario:
Assume the first curtain has developed an edge curl. The photographer sometimes advances after each shot and sometimes doesn't. A shot is taken and the camera is immediately wound on. He carries the camera around for a while. The lens is wide open and he doesn't have a lens cap. That shot has a bit of fogging. The first curtain with the curl was behind the lens for a while and more prone to leak light. After the next shot, the user forgets to advance the camera, meaning that now, the good second curtain without a curl is behind the lens, which is much more light tight because it doesn't have a curl plus the design means that curtain is a little closer to the plush strip. People often tell us that they are confused because sometimes they can have problems and sometimes not, even on the same day and same lighting conditions.
If the problem is really bad, maybe one of the plush strips has dropped off. If that happens they can easily become entangled in the shutter mechanism. See the pictures below. I was planning to dismantle this camera just to show the plush strips and baffle, but you can see clearly how the top plush strip has become detached and entangled in the shutter mechanism. Sometimes we see the odd missing plush strip which has been retrieved but not replaced, increasing that air gap between the baffle and shutter, and increasing the likelihood of a light leak. When we dismantle a camera, a slight poke with a pair of tweezers often causes them to drop off because the glue has dried out. This is why we always remove and re-glue them and in many cases replace them altogether. Service replacements over the years also vary in quality. Modern, off the shelf velvet ribbon is often used which has much shorter pile than the original and are far less efficient.
The following picture shows what happened when I simply touched the remaining plush strip with my tweezers!
Focal Plane Shutters and the SLR
Horizontally travelling cloth focal plane shutters were once all the rage. Almost any good camera would use them but in most cases, they were fitted to single lens reflex cameras and they had one advantage – the reflex mirror. This cast such a shadow that there was little chance of any light getting through even the most poorly designed shutter.
The Copal Square Shutter Design
In 1965, the Copal Square shutter was released. Instead of a complicated arrangement of rollers, drum and fabric curtains, it used an arrangement of metal slats that resulted in a vertically travelling slit all built into a single, compact mechanism. It was light, reliable and capable of faster shutter and flash sync speeds. Leica adopted these shutters in the Leica 'R' series, Minolta based, of course and experimented with the Seiko variant of this shutter in an M6 prototype. This would have allowed for the addition of automatic exposure because such shutters are easily adapted to be timed electronically. Unfortunately, without a reflex mirror, these shutters were far less opaque than the original Leica shutter and wide-angle lenses rendered them useless. That is why Leica kept the original shutter design, adapting the release mechanism using electromagnets for the M7. The Japanese company Cosina who produced the Voigtlander Bessa 'L' and 'R' cameras decided to go with the square type shutter and they were well aware of their leaky attributes but very cleverly solved the problem by using a shutter with two sets of curtains.
How Nikon approached the problem
I was interested to find out how other camera manufacturers approached the opacity problem of horizontal focal plane shutter. Nikon had been concerned about this issue for a long time, which is surprising because in the early 1960's, the Nikon F, a SLR that offered good shading to the shutter, had already gained legendary status, and the premium SLR market was now the company's prime focus. The Nikon F shutter was perfectly sufficient for SLR use but they still found shutter opacity to be of concern and continued to make improvements. When the F2 was introduced in 1971, Nikon announced that they had completely solved the problem of shutter light leaks. I believe their adoption of teflon coated titanium shutter curtains was part of this solution as they allowed for a certain type of contact baffle strip.
The general layout of the Nikon shutter is the same as the Leica with a baffle & baffle Strips, curtains and film aperture arrangement. Instead of velvet baffle strips, Nikon employed two sets of very nicely made, low friction, fabric-backed silicone rubber flaps which were not only attached to the back of the baffle but also on the body casting of the film aperture. As you can see in the image, the baffle strips are mechanically secured to a plate which is then screwed onto the back of the film chamber. This part is from a 1973 camera and as you can see, there is no sign of wear at all and that is fairly typical. Even though this level of over-engineering was not strictly necessary, these improvements resulted in a focal plane shutter that was almost as light-tight as a leaf shutter.
Talking about Nikon in this way isn't meant to be a criticism of Leica and there may be some who read this and say something along the lines of...
“Rubbish, a Leica shutter is perfectly light-tight because Leica made it and they are the best etc etc. If it leaks light at any time, then it must be broken and if the engineer can't fix it, they don't know what they're doing”.
Consider this: Nikon went to great lengths, in perfecting the focal plane shutter on the F2. They announced that shutter light leaks were a thing of the past. The shutter was also protected by the large reflex mirror. Nikon couldn't have been too sure though, because page 30 of their instruction manual warns the user to "shield the lens opening from bright light when changing the lens". Nikon were still a little concerned about the F2 shutter opacity in bright light. It stands to reason therefore that a non SLR with a simpler shutter design can and will leak light occasionally if care isn't taken - changing lenses, lens caps etc. You may lose the very odd frame. Don't worry, you don't need to spend £££'s getting your camera fixed.
Japan's plan for global domination!
We mustn't forget that Leica developed the most successful shutter technology of all time. By standing on the shoulders of giants, companies like Nikon would take these innovations, re-engineer, refine and prepare for mass production, with one aim, global market domination. To do this, quality and reliability was paramount and this would take serious investment. This came at a bad time for Leica. Their business was seriously affected by Japanese competition. Leica cameras were expensive and generally out of the price range of most enthusiasts so became a somewhat niche market. There was a skill shortage and manufacturing processes meant productivity was low but in 1956, Japan launched a five year plan to completely modernise all manufacturing capabilities in order to boost productivity and this all happened while there was a favourable Yen exchange rate. Any further investment by Leica would only push prices even higher.
When Leica did a deal with Minolta to manufacture the Leica CL, it took several months to make necessary design changes in order to take advantage of Minolta's advanced production line technology. This had to be done to make the camera profitable. The original CL had been geared towards relatively small batch production utilising mainly hand assembly techniques.
The new Leica 'improved' non-velvet baffle strip
When the M6 was introduced in 1984 Leica eventually improved shutter opacity by re-designing the plush strips. Instead of velvet, flaps of black plastic material was used, a simplified version of the Nikon baffle strips. They were effective because they rest against the curtains, reducing light leakage considerably.
We ran out of replacement M6 baffle strips a few years ago and I contacted a Leica repairer of considerable international repute, to ask if by any chance he had any stock to spare. I was very much amused when he emailed me a picture of a black plastic film packet and underneath, the words “this is what I use”. I always presumed that the M6 baffle strips were made from some specially formulated material but apparently not. We prefer to use a professional light blocking material called Carbonfeather for this purpose. Film bags seem to be the same as heavy duty refuse sacks!
Vertical bands and odd light leaks on M6
To be fair, the plastic bag material is flexible, low friction and has excellent light blocking capabilities. It works quite well for a while. Eventually however, the material becomes less supple and the constant friction caused by the shutter causes the surface of these baffle strips to become rippled. When this happens, light can leak through those ripples. So instead of a diffuse horizontal band, you get a horizontal band of diffuse vertical streaks! It just wasn't engineered for this purpose.
Another problem is that cracks can appear. These can catch the edge of the shutter curtains, causing them to snag momentarily, causing vertical bands of different exposure to appear on your images. Not light leaks as such but a problem caused by the material that is supposed to prevent them.
Times change and there are now materials available that are capable of doing a better job. We are working on our own plush strip replacements which are dense like velvet but with longer pile. These will reduce the chances of light leaks through the shutter dramatically. As soon as these become available, they will be fitted during a service free of charge.
Blacker than Vantablack VBx
The other thing that we've already introduced, is the use of a specialist matt black coating to be used on the external as well as internal parts of the baffle. Paint manufacturers often market what they laughably refer to as matt black paint. Most are completely unsuitable for light baffling of optical equipment. Using technology developed by Koyo Orient Japan, we have an ultra black coating method that results in light absorption at a rate of up to 99.4%. Below, you can see the difference between a regular M3 baffle and one we have serviced and repainted. When we service your Leica M, the baffle will be coated using this method at no extra cost.
One of the reasons I wanted to introduce this ultra matt black technology was because of an old 1960's technical report by the Japan Camera Industry who carried out a review of sorts on the Leica M2. The report was on the whole very complimentary but on two occasions the baffle was mentioned. The curved areas were regarded as being a potential source of specular/diffuse reflection directly onto the film area during exposure. One of their recommendations was at least to apply ridges or texture to the curves of the baffle to reduce this possibility. This advice was never heeded of course. Our surface coating will address this concern. This isn't a light leak problem either but any scattering of light behind the lens has the possibility of exposing darker areas of an image, resulting in a potential loss of contrast.
There is one final type of shutter light leak that one of our Facebook group members reminded me of. I thought I should mention that here. Some of you may have noticed that the edges of the 'M' shutter curtains have interlocking metal parts, making a very light-tight seal. The interlocking part is called the labyrinth. LTM cameras rely on overlapping the edges of the shutter curtain. On a Leica, this is known as a self-capping shutter. They remain overlapped while the shutter is being cocked. Because the first curtain lays behind the second, if you advance the camera after each shot, it is possible to leak light between the shutter edges, leaving a white shadow on the edge of your frame. It is very unlikely to happen if you don't advance between shots. Like everything else mentioned here, it may be something that never happens to you or in the case of our Facebook friend, apparently it happened a lot. I suspect the amount of overlap of the curtains may have been insufficient, allowing light to penetrate more easily.
We offer the finest service available for any Leica rangefinder film camera. Our prices are transparent, we do far more than any so called CLA and our 1 year transferable guarantee is legendary. You can book a service here or give me a call on +44 (0)7411 131386. I hope you found this interesting. Next, I will be writing about rangefinder calibration and how often it should be done. Spoiler alert - once in a blue moon. Alan.