Recently I purchased an old manual focus lens for my Canon DSLR. The seller described it as having a bit of dust inside, so I was able to get it for relatively cheap. This is the picture the seller gave for the inside of the lens:
As it turns out, the dust was fungus. I did a bit of research and I discovered that I could use isopropyl alcohol to kill the fungus and clean the lens elements. On older lenses, this may damage the coatings, but I decided that first, the fungi may already have damaged the coating so this wouldn’t matter much, and second, this lens was not a “Nikkor Kogaku Japan” version so it was made later and the coating probably would be more resilient.
I found Flickr member c995’s set called “DIY 28mm Series E Lens disassembly” and adapted it for this lens. First, I put duct tape on the front of the lens where the lettering is. I then placed a folded up piece of toilet paper to protect the front element from any scratches.
I found a rear lens cap that fit in the front of the lens. I applied downward pressure onto the lens and twisted counterclockwise.
The front element set screwed out without any problems. It took a bit of elbow grease, but nothing serious. (Be careful when it is unscrewed–tip it out gently so it does not fall out on the ground!) This set contains elements that are cemented together. I suspect that they are housed in plastic to make sure that they remain in alignment unless disassembled by a professional, which I am not, so thank goodness.
Here you can see the fungus on the rear of the front element set. I used a Q-Tip and some rubbing alcohol (70% isopropyl alcohol) and cleaned those guys right off. I used a microfiber cloth that came with my glasses to wipe off residue after the alcohol evaporated. Ideally I would throw the microfiber cloth away in case some of the fungi were transferred to the cloth, as I wouldn’t want to use it again, but I don’t have a stash of microfiber cloths. As long as I don’t keep the one I used in a warm and humid environment I should be OK.
This is what the lens looks like from the front without the front element set. Notice the diaphragm. It is free of oil, as it should be.
I unscrewed the five screws holding on the mount portion. (You can see that to the right.) This allowed me easier access to the rear element, which also had a little bit of fungus on it. Same process with the Q-Tip, rubbing alcohol, and microfiber cloth.
Another shot of the lens mount portion:
I reversed the process to re-assemble the lens. I let it sit in sunlight for a few days in the hopes that the UV would kill any stray and susceptible spores. I then let it sit in a Ziploc bag for a few days with silicone desiccant to remove any moisture from the lens. I have yet to receive my Nikon F to Canon EOS adapter, but I will test out this lens as soon as I receive it.
From this one data point, I’ve gathered that old manual prime lenses are easy to disassemble and clean. Granted, I didn’t mess with the focus or the diaphragm, and I haven’t tested the lens yet to see if I reassembled it correctly, but it seemed fairly straightforward. The lens was only $15, so I figured I would either have a good deal by fixing it myself, or I would have spent a little bit of money on a project lens, learning how to fix old manual primes. I would encourage you to not be afraid to disassemble an old manual focus prime lens! If it’s cheap or in need of repair (or perhaps beyond the point of repair), take it apart and see how it works! Make sure to document your process so you can put it back together. And have fun!