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07-08-2011, 09:47 PM   #1
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How difficult to clean aperture blades SMC-F 50mm f1.7

How much of a bitch is it to clean the aperture blades on a SMC-F 50mm f1.7? I can get one for about a hundred bucks, but the blades are sticky.

Is it possible to do from the front? I'd really rather not take off the bayonet if it can at all be helped.

Charles.

07-08-2011, 10:21 PM   #2
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QuoteOriginally posted by ChopperCharles Quote
How much of a bitch is it to clean the aperture blades on a SMC-F 50mm f1.7? I can get one for about a hundred bucks, but the blades are sticky.

Is it possible to do from the front? I'd really rather not take off the bayonet if it can at all be helped.

Charles.
You need to remove the glass elements in front and the back of the diaphragm assembly in order to clean the aperture blades. Liberally dowse the blades with naptha, work the blades briskly a few times and let dry completely. Check blade movement when dry and repeat process until you are satisfied. Personally, I won't attempt to clean any AF lenses on my own. I would send it out to a qualified person to clean the lens.

Thanks,
07-08-2011, 11:58 PM   #3
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I haven't repaired this lens b4 but each Pentax AF lens has a very fragile contact brush which can be torn if not disassembled properly. Pentax probably don't stock the parts for this lens anymore so be careful.
07-09-2011, 02:16 AM   #4
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I just pull the lens apart and use zippo lighter fluid to clean oily/dusty aperture blades - apply the fluid with light strokes from a kolinsky sable brush.

07-09-2011, 08:03 AM   #5
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QuoteOriginally posted by ChopperCharles Quote
How much of a bitch is it to clean the aperture blades on a SMC-F 50mm f1.7? I can get one for about a hundred bucks, but the blades are sticky.

Is it possible to do from the front? I'd really rather not take off the bayonet if it can at all be helped.

Charles.
Yeah, all those brass springs and contacts flying around. It really makes you wonder how they assembled all those contacts at the factory.

You can get to both sides of the aperture blades on the F50/1.7 without dealing with the mount. On the front, focus to minimum distance. Remove three screws on the side of the barrel, and the filter ring comes off. I was able to unscrew the front lens group with just my hands at that point. Or, it looks like the beveled part around the front element might unscrew, like on the older 50s, to reveal slots for a spanner wrench.

At the back, remove the light shield by unscrewing the three screws. One is by the orange alignment dot and the other tow are 120 degrees away from that one. Then you might be able to focus to infinity and get a grip on the rear lens group, and unscrew that. Or there's spanner slots for this group.

The more access you have to the blades, the easier it is to clean them. Ideally you should remove them entirely but it's a risk/reward thing. They'll be clean and you can clean the entire area, but can you get them back together without damage? A couple of sessions with naptha with the blades in place is usually enough. Clean the lens elements facing the blades too, in case they have a coating of oil you can't see.
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