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04-16-2009, 10:58 AM   #1
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SMC 55mm Inaccurate focus length issue

I got an manual Pentax SMC f1.8 55mm lens, great lens, but just found one issue on it. The lens's focus is fine from closest to infinite. but focus distance marking doesn't correspond to the actual focus length. I test to different focus lenght, only at closest distance(0.45m or 1.2ft), the actual distance is same as the marking in the lens. other than that, the marking doesn't correspond with the actual focus distance. At infinite, the marking list the distance as (~6.3ft or 1.8m). Any one know the problem here. Would previous owner replaced it with the wrong ring?

04-16-2009, 11:57 AM   #2
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Just out of curiosity, does the lens have a shrouded distance scale, and if so, does it move at the same rate as the focus ring itself? I have a Takumar where the shrouded scale ring isn't tightly coupled and slips - I can use my finger to move it - and so I don't get a good scale indication. Fixable with the right screws I gather, but I haven't seen a need to do so.
04-16-2009, 02:45 PM   #3
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QuoteOriginally posted by Nesster Quote
Just out of curiosity, does the lens have a shrouded distance scale, and if so, does it move at the same rate as the focus ring itself? I have a Takumar where the shrouded scale ring isn't tightly coupled and slips - I can use my finger to move it - and so I don't get a good scale indication. Fixable with the right screws I gather, but I haven't seen a need to do so.
It needs to be glued. Probably a rubber focus ring version? It's an easy fix once you get to it, but you have to take off the trim ring -> filter ring -> focus ring, reglue, then focus ring -> adjust infinity focus -> filter ring -> trim ring.

I hope this is what's wrong with winglik's lens because I can't think of any other way it could be broken. The focus ring on the 55mm lenses turns about 270, more than any of my other non-macro primes. He's missing almost 90 of that. Because of this large rotation, I doubt someone has swapped parts with another lens, unless the rest of the lens is a 50mm f1.4 K. There just aren't that many common parts among different lens models. Also because of the 270 sweep, the lens shouldn't focus anywhere near infinity or simply need an adjustment.
04-16-2009, 06:46 PM   #4
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I took the lens apart tonight, The problem was on the loose on back lens, after tighten it up, everything works.

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