| Author | Message | ||
     Jim Brokaw Rating: N/A |
No oil. Aperture blades are mostly made to work dry, though its not so important when they are not SLR 'instant-return' apertures. The many thin leafs of rigid steel overlap quite a bit, and even a small amount of oil creates a tremendous amount of 'stiction' between the leafs (relatively speaking...) This stiction can easily cause the leafs to bind against each other and then shear off the little pins upon which they pivot. If that happens you can only replace the leaf, which is a very intricate and delicate job. Sometimes a thin coating of very fine powdered graphite is recommended to help lubricate the leafs overlaps, but in most instances I've found this is not necessary. What IS necessary is to completely and thoroughly clean out all the oil from both the visible area of the leafs and the rotating and pivoting pins and base area of the leafs... this can require disassembly and separation of the aperture mechanism from the shutter mechanism. In many cases you remove the 'guts' of the shutter which then reveals the leafs and associated rings which manipulate them to open and close the aperture. Soak the leafs and pivot areas and rings with naptha (Ronsonol) and dry with bits of tissue or canned air. Make sure you get ALL the oil and crud out. This is easiest to do if the shutter mechanism is separated, but IMO you don't generally need to disassemble down to the individual leafs unless there is evidence of rust or corrosion on the leafs. I've had success polishing leafs smooth and removing rust with a pencil eraser, applied carefully to the individual leafs against a slightly padded backing of paper towel... The iris aperture is really a quite clever design, but can be tricky, and even more of a hassle to deal with when the leafs are not flat but domed as they were in an old Leica lens I disassembled... If you do this carefully and if there is no mechanical binding in the linkages and pivoting areas you should be rewarded with a smooth working light touch aperture. Take your time and study the way it goes together when you get in there, its sometimes not obvious how the leafs overlap (sometimes there are 'left-way' and 'right-way' leafs that alternate, for instance. Most SLR apertures are simple with few blades, but the old lenses with 11, 13, 15, or even more leafs can be a real pain to deal with. Search the archive for my story of how I got that Leica lens back together... which is how its going to stay! |