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02-25-2009, 12:20 PM   #1
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old lenses- that little plastic white dot?

I have a few old K-mount lenses- 'K,' M and A series. On the focus scale ring, to the right, they have small plastic white/yellowed white dots- ~4mm in diamter, hemisperical.

Does this dot serve any function? It fell out on a 24mm lens and I wonder if I need to replace it, or at least plug the opening. Thanks!

02-25-2009, 12:23 PM   #2
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Are you talking about the dot above the 2.82 in the picture below?

02-25-2009, 12:27 PM   #3
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QuoteOriginally posted by dandaniel Quote
I have a few old K-mount lenses- 'K,' M and A series. On the focus scale ring, to the right, they have small plastic white/yellowed white dots- ~4mm in diamter, hemisperical.

Does this dot serve any function? It fell out on a 24mm lens and I wonder if I need to replace it, or at least plug the opening. Thanks!
its an alignment bump. it was designed to allow someone to mount and lock the lens in the dark. you align the bump with the lens release lever by touch then turn and lock. however this is useless on pentax digital SLR's (maybe even some later film SLR's?) because the lens release lever is no longer in the same place. it has been moved down and a little to the right making it misaligned with the bump. it has no operational effect. purely cosmetic. covering it up is your choice.
02-25-2009, 12:27 PM   #4
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I think it is just a little nub to grip the lens when rotating it for mounting/dismounting?

02-25-2009, 12:28 PM   #5
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QuoteOriginally posted by dandaniel Quote
Does this dot serve any function? It fell out on a 24mm lens and I wonder if I need to replace it, or at least plug the opening.
The raised dot is only for ease of alignment when you're attaching the lens to the body. The dot should be at 8 o'clock position, where the lens release button on the film cameras is.

You can just plug the hole.
02-25-2009, 12:30 PM   #6
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QuoteOriginally posted by dave9t5 Quote
I think it is just a little nub to grip the lens when rotating it for mounting/dismounting?
it can also be used for this purpose.
02-25-2009, 02:13 PM   #7
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Wow, quick replies! Thanks.

Yes, Apollinax, that yellow dot in your photo is exactly the piece that has disappeared. Sounds like nothing to worry about.

Thanks again to everyone for the info.

Last edited by dandaniel; 02-25-2009 at 03:18 PM.
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