The Bessa came out of an auction lot with the lens visibly filthy and the unmistakable look of a fungus colony living between the elements. A torch held to one side of the front element revealed a thick organic web across the inner surface. The shutter still worked, the bellows were fine and the body had cleaned up properly once I had got the dirt off it. The only thing standing between me and a working 6x9 folder was the lens. So I took it apart, cleaned it and put it back together. The lens went from cloudy to clear and the Bessa is now one of my favourite cameras in the cupboard.
This piece is the walk through. What fungus is, what tools you need, how I worked the Bessa I lens apart, what solution I used to kill the fungus and how I re-calibrated the focus ring afterwards. It is also a record of what I have learned since, much of which has come from the people who left comments on the original video. The comment thread there has turned out to be one of the more useful conversations on lens repair that I have stumbled into, and I will weave the most useful contributions in throughout the piece.
The companion article on shooting the cleaned-up Bessa is over here.
What lens fungus actually is
Fungus in a lens is what it sounds like. A microscopic colony of fungal organisms has set up shop on or between the glass surfaces of the lens. Given moisture and a food source (typically the organic compounds in the lens lubricants and old greases) it will grow. The thicker the colony, the more light it scatters and the worse the image becomes. Left for long enough the fungus can etch the lens coating itself, at which point you cannot remove it without grinding the coating back. One commenter, skypetch, asked whether the process I describe here fixes etched fungus. The honest answer is no. Once the coating has been eaten, the optical damage is done.
The good news is that most fungus you encounter on an old folder is not at the etched stage. It is a surface growth that can be removed with the right solution, and the lens behind it is usually fine.
There is a separate question of why some lenses develop fungus and others do not. The answer, as Michael Dimmitt explained in the comments, is that fungus needs moisture and something organic to eat. The organic-based greases and lubricants in old shutters and focus mounts break down over time. The volatile compounds evaporate and the organic residues left behind become food. The moisture comes from the environment, which in a typical home means the water released into the air by everyday activities like cooking and bathing. A camera stored in a warm, damp cupboard for fifty years will grow fungus. One kept on a cool dry shelf with good ventilation will not.
A quick note on which lenses you can safely treat with this method. The Bessa I lens is uncoated or has only a primitive single coating. The ammonia and peroxide mix described below is fine on uncoated glass. It is not safe on modern multi-coated lenses, where the soft coatings can be damaged by ammonia. I would not recommend this method on anything newer than about 1960, and even then I would test with peroxide alone first.
Tools
You will need a lens spanner. The cheap ones (the adjustable two-pin sort with the pins sliding on a slotted bar) are dangerous. Mine slips and wobbles in use, and has put more scratches on more cameras than any other tool in the bench. Use it lightly, just enough to break the initial seal on a retaining ring, then switch to a small flathead screwdriver to back the ring out properly. The commenter michaelprzewrocki4195 had even stronger views than I do on this design (“the worst lens spanner. wobbly. dont use”), and I cannot really argue. Michael Dimmitt pointed out that the proper tool is a white nylon spanner of the sort used in actual lens assembly work, with metal teeth embedded in a solid nylon block to avoid slippage and scratching. You need a different size for each ring, which is why I do not own a set. If you are taking apart more than one lens you probably should.
The other useful tools are a set of rubber friction wrenches (conical rubber cups that you press onto a stuck ring and twist), a torch for spotting fungus, a soft clean cloth to put parts on as they come out and a magnifier of some kind for the small grub screws. I used a pair of cheap magnifying specs and I should have used them earlier in the process than I did. Russell Sprout asked in the comments where to get them and I have sent him a link to a similar pair on Amazon.
For the solution itself you need ammonia, hydrogen peroxide, a glass or plastic bowl, water and cotton buds. Both chemicals are nasty. Open the bottles outside or with a window open and a fan running. Wear gloves. I would also suggest eye protection if you are going to be working closely with the bowl. The smell of household ammonia at concentration is genuinely aggressive. The commenter 1973sonvis from Norway pointed out that 3% peroxide is the most you can buy over the counter in some countries and 6% requires explaining yourself to the pharmacist. Mine came off eBay at 15%, which is significantly stronger than you actually need.
Taking the Bessa I lens apart
The standard layout for a folder lens of this era is one or two glass elements at the front and the back, with the aperture and shutter blades sandwiched in the middle. The shutter and aperture assembly is held into the front standard by a single retaining ring at the rear. Everything that needs to come apart for cleaning unscrews from there.
I started with the rear retaining ring. The lens spanner pins fit into the slots in the ring well enough to give it a quarter turn. After that the screwdriver did the work. With the retaining ring off, the entire lens, shutter and aperture assembly lifts out of the body towards the front.
The rear lens element comes out next. On the Bessa it is a single group with no notches for a spanner, which means it has to come out by twisting the metal frame it sits in. I put a rubber wrench on it and turned. It came out cleanly. The element is slightly convex on one side and concave on the other, with the concave face pointing towards the back of the lens. I put it on a soft cloth in exactly the orientation it had come out in. This is the most important habit in any lens disassembly. Glass elements are not symmetrical and they will not work if they go back the wrong way round. Every time you take a piece out, you put it down in a way that records which face was forwards and which was back.
The front element on this lens sits underneath the focus ring. To get at it I had to remove the focus ring first. There are three tiny grub screws around the focus ring collar that hold it onto the lens housing. Loosen them and the ring lifts off. Note that removing the focus ring means losing the relationship between the distance markings on the ring and the actual position of the lens. You will have to re-calibrate this afterwards. I will come back to this.
With the focus ring off, the front element unscrewed in its housing with the rubber wrench. Same routine as before, with the concave face pointing back. Onto the cloth in the right orientation.
Inside the shutter there was a third element that I could not get out of its frame. This is the one with all the fungus. I tried the rubber wrench, and gentle persuasion with a pair of pliers wrapped in tape. It would not budge. Rather than risk breaking the glass I left it where it was and cleaned it in situ with a cotton bud dipped in the solution. The commenter Paul Taylor described the same kind of frustration with stuck elements and I echo his sentiment. Some lenses simply do not want to come fully apart and the right answer is to stop pushing.
The cleaning solution
I work with 15% hydrogen peroxide because that is what I have. The actual concentration you want for cleaning is closer to 3%, which is what most people use. So I diluted mine fifty-fifty with water in one bowl, and made a fifty-fifty mix of household ammonia and water in another. Then I mixed the two together into a single working solution. The peroxide handles spots of fungus and the ammonia takes care of general haze. The combination works on both.
A quick maths confession. The commenter marxoniomizu pointed out in the comments that by diluting the peroxide twice (once with water, then again with ammonia) I had ended up closer to a 5% peroxide mix rather than the 7.5% I had announced on camera. He is absolutely right. I would not pretend my mental arithmetic is impressive. As it turns out, 5% peroxide is well within the working range for cleaning fungus, so the maths error did not affect the result. But for anyone planning to do this, the correct way to think about concentration is to work out what dilution you want in the final mix, then halve it again when you combine the two solutions.
The two free elements went straight into the bowl. They started fizzing immediately. Within a minute the fungus had visibly lifted off the glass and was floating as small clumps in the solution. I left them for two or three minutes, then lifted them out with a cotton bud and dropped them into a second bowl of clean water for a rinse. From the rinse they went onto the cloth and I dried them carefully with a lens tissue.
The stuck element got the cotton bud treatment. Dip the bud in the solution, work it around the fungus, leave it for a minute, repeat. It took longer than the bath did but it worked just as well. The Ringer1982 comment on the original video makes the case for doing it this way for all the elements (“a few millilitres of the solution on a q tip would work for all of those lens elements”). He is not wrong. A bath is faster but it uses a lot more peroxide and ammonia, and the cotton bud approach is gentler on the glass. Since the video I have moved closer to this approach myself. I now reach for straight 15% peroxide on a cotton bud first and only break out the ammonia mix if there is haze that the peroxide does not touch. The ammonia is seriously brutal stuff and the less of it I have to open the better.
Putting it back together
This bit is mechanical. The elements go back in the reverse of the order they came out, in the same orientation they came out in. The shutter assembly goes back into the lens housing and the retaining ring secures it. The front element screws back into its frame, then the focus ring slips back over the lens body and the grub screws bring it tight.
Hold the assembly up to a torch and check the elements look clean and properly seated. If anything is misaligned you will see it immediately as a wobble or a tilt in the reflections from the glass.
Re-calibrating the focus ring
This is the bit most people skip in tutorials and it is the most important step for a folder. Because I removed the focus ring during disassembly, the distance markings on the ring no longer match the position of the lens. Infinity might now be at one metre on the ring, or one metre might be at the lower limit. The focus ring needs to be reset against a known reference.
The method is straightforward. Open the shutter on bulb and stop the aperture down to whatever you have set. Stretch a piece of plain paper across the back of the lens where the film would normally sit. This acts as a basic ground glass. With the lens pointed at something a known distance away (for the infinity check, I used a house about thirty metres from my back door) the lens projects an image onto the paper. You can see whether the lens is in focus on that image by adjusting the focus screw on the front standard and watching the image sharpen and soften.
Once you have found infinity on the lens, you loosen the grub screws on the focus ring just enough to rotate the ring against the lens body without moving the underlying focus mechanism. Then you turn the ring until the infinity mark on the ring aligns with the arrow on the lens barrel. Tighten the grub screws. You are done with infinity.
It is worth double-checking at a measurable closer distance. I picked the corner of the picnic table in the garden and measured it at ten feet from the film plane. After refocusing I looked at the focus ring. It read nine and a bit feet, which is close enough to be within the precision of my measurement.
A few notes from the comments here, because this section attracted the most discussion of the whole video.
waynesimon7096 pointed out, sensibly, that tracing paper works better than plain paper for this trick because it is more translucent. The image projects through it more clearly. I did not have any tracing paper at the time. I would now. The commenter aeyb701 went further and suggested either parchment paper cut to the size of a 120 frame (which holds tension across the film plane in the same way the film itself would) or a piece of clear plastic sheet scuffed lightly with fine sandpaper to make a homemade ground glass. Either is cheaper than a real ground glass focusing screen.
jparsonsfilm pointed out that the Bessa I focus mechanism actually stops at infinity, so I could have simply wound the lens all the way out to its stop and aligned the ring from there. He is correct. I had not realised this at the time. The reason I went the paper-on-the-back route is partly that I did not know the lens had a hard stop and partly that I enjoy making jobs more difficult than they need to be.
nestingstarling5895 made a genuinely useful point that goes against most service manuals. Rather than calibrate at infinity, calibrate at a known intermediate distance like ten feet or three metres. The reasoning is that you can measure ten feet exactly with a tape measure, but you cannot really know whether the object you are focusing on at “infinity” actually is at infinity for that lens. Setting the ring against a measured distance is more reliable. He keeps split-image focusing screens for 35mm and 120 cameras for exactly this purpose, tapes them to the film plane and focuses through a magnifier. I have since picked up the same habit for closer focus checks, though I still use infinity for the primary calibration.
erikboon6549 described a more advanced method, which is the collimation technique used by camera technicians. You set the folder lens at its infinity stop and then look at the film plane (with a piece of film with an X marked on it) through a 35mm SLR with a 50mm lens focused at infinity, with diffused light shining through the folder lens from the front. If both lenses are at infinity the X is sharp in the SLR viewfinder. Erik credits a video by Dennis Workman that goes through the technique in detail. I admit my brain works in a way that struggles with optical theory of this kind. I followed Erik’s explanation up to a point and then had to step away from it. I will get there.
What I would change if I were doing it again
A few things I have learned since this video that are worth flagging.
I now mostly use straight 15% hydrogen peroxide on a cotton bud rather than a bath of diluted peroxide and ammonia. Rainer (rewahl) uses 3% peroxide on a cotton bud and gets the same result. The ammonia is the most aggressive part of the mix and I avoid it unless there is haze that the peroxide alone will not shift. If you can buy 3% peroxide at the chemist near you, that is the sensible starting concentration. If you have to go to eBay for 15% like I did, dilute it down before you start.
Second, the technique does not transfer to modern coated lenses. Several commenters asked about this and I responded with the same caveat each time. Soft modern coatings are damaged by ammonia and I would not risk it on anything newer than about 1960. For modern lenses with serious fungus you are probably looking at a professional service or replacement.
And finally, prevention beats cure. Store cameras dry. A small bag of silica gel in the camera bag and a cool dry shelf for storage will keep most fungus from getting started in the first place.
The comments are worth your time
The original video has accumulated a useful discussion thread over the past few years, and it makes one thing very clear. Everyone has a slightly different way of doing this work. There are people who swear by 3% peroxide alone, people who use only ammonia on a cotton bud, people with specialist nylon spanners and split-image focusing screens for proper benchwork, and people who, like me, are working it out as they go with whatever is in the kitchen drawer.
If you are about to do your first fungus removal I would recommend reading the comments on the video itself alongside this article. There is more wisdom in there than I can fairly summarise without turning this piece into a comment compilation. Peter (theoldfilmbloke), Paul Taylor of New Zealand, Rainer in the Black Forest, Wayne in Canada, the lens technician panjiirawan1060 in Indonesia, michaelprzewrocki4195, Michael Dimmitt, jparsonsfilm, nestingstarling5895 and Erik Boon between them have left a generous body of advice. Thank you all.
The Bessa I, three weeks of patience later, is sharp, clean, working and delightful to shoot with. The companion piece on how it actually shoots is over here.