Canon lenses for their rangefinder line most often are found in not so mint state (you might want to look up my posts about haze/fungus) … well at least for us bargain hunters.
Many older Leica thread mount lenses from Canon suffer from haze and fungus.
There are many theories around why haze is common … many blame it on the evaporation of the lubricant used, or the type of glass used which is prone to corrosion by moisture. It tends to form on the element face above or below the aperture. In most cases haze can be remove with just a simple cleaning, but if it attacks the glass or coating the only way to fix this is by getting the element polished (which is very expensive to get done). The lens can sometimes still be usable but it will affect contrast and sharpness of the image … makes for an OK soft focus lens for portraiture.
Fungus, well that’s just due to the storage condition of the lens. Many of those found and up for sale have been lying around in some closet for decades.
For those that want to attempt cleaning the lens (I say attempt as in many cases the haze or fungus will never be removable), these older Canon lenses are not that difficult to take apart. Note that there are many other websites/blogs that go over this already, but I thought I would add it to my blog anyway.
Here is info on the Canon 50mm f/1.8 chrome model.
Tools: spanner wrench, rubber lens tool, blower, lens cleaning stuff, Ronsonol.
All access can be done by going through the back.
Unscrew, counter-clockwise, the retaining ring and pull it out.
You can then pull off the entire focus helix assembly.
Note that there is a brass shim around the lens collar. Do not lose or damage this. This is a specifically sized spacer.
You can clean some of the old grease off of the focus helix and apply new stuff.
I didn’t go as far as complete disassembly to do a thorough cleaning.
The rear elements are in two pieces
Unscrew, counter-clockwise, the top lens group.
Unscrew, counter-clockwise, the lower lens group.
Now you have access to the rear of the aperture. I you open up the aperture you can then have access to the rear of the front lens element group.
Put some Ronsonol on the aperture blades to clean off any oil (if there is any).
Put everything back together one step at a time. Each time you should visually examine for dust.