For those who have done this:
I've cleaned up oil on the aperture blades of an old 50mm nikon RF (Range Finder) lens, some blades were stuck together and the aperture was no more circular. The lens was restored to a normal condition and I took the opportunity to clean up the inner lens elements. I'll talk about this lens, other lenses may be trickier to deal with.
How difficult is this?
It is tedious, but I wouldn't rate it as very difficult. You have to be armed with patience, and be ready to disassemble and reassemble delicate parts.
What pointers do you have?
Work in a clean and as dust free environment as possible! Bathroom is usually the least dusty environment in a house. If you have an air cleaner, turn it on in advance.
- camera to take pictures of all the steps you are taking during disassembly (to ease reassembly)
- adjustable spanner wrench to unscrew the retaining rings of the lens elements (a photo of which is shown below)
- micro screwdrivers: usually Phillips ( #000 or other size)
- one or two pairs of tweezers to manipulate the aperture blades / leaves
- lens cleaning tissue to put the lens elements you'll have removed
- a pair or two of gloves to keep finger oil from the lens element
- small plastic container for the aperture blades
adjustable spanner for opening the lens (here from Thorlabs)
Depending on the lens, the diaphragm may be located closer to the front or the back of the lens. In my case it was accessible from the front of the lens.
There are some screws on the outer body of the lens toward the front, you will have to remove those so that a kind of shell can be removed.
Unscrew the front lens element with the adjustable spanner, in my lens there was another lens element (an achromatic doublet, 2 lens elements, in this case, glued together) to be removed as well. Note the orientation of the lens elements (the front and back surface curvatures are likely different).
I then could see the actual leaves of the diaphragm. Using tweezers I've removed the whole aperture, and then proceeded to cleaning each one individually with a clean lint free cloth. I didn't use any cleaning liquid so that a very thin film of oil would remain on the blades.
Some photos of the process:
The aperture diaphragm as it originally was, that is out of shape.
The blades and rotating ring with spigots.
You then proceed to the reassembly, one blade at a time.
Remember to take photos of each steps, especially when you reach and remove the aperture.
What could go wrong?
- damaging a lens element when disassembling the lens
- putting back a lens element in the wrong orientation
- dust from the environment settling on the lens elements surface
- losing or damaging an aperture blade
- being unable to reassemble the whole aperture ring
Now: as mentioned in another answer, the difficulty is of another order with modern lenses. I've disassembled a damaged canon lens from a friend and many parts were glued and unaccessible.