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06-19-2011, 08:09 AM   #1
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Whats the pimple on the F primes for?

I recently got a Pentax-F 50/1.7. There is a pimple on the right next to the focus scale window- does anyone now why that's there? I looked at the F-lens manual (PENTAX MANUALS) but there is no mention of it.

06-19-2011, 08:19 AM   #2
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My guess is that is a help to mount the lens on a body in the total darkness : look at the red point, if you align the pimple and the button to release the lens (when it's on the body), the red point will be aligned with the red point of the body
06-19-2011, 08:22 AM   #3
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+1 ^ these were made for film cameras.
On the m and a series it is a more prominent light colored bump.
06-19-2011, 09:18 AM   #4
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QuoteOriginally posted by chse Quote
pimple


That's a "holdover" from Pentax K manual focus lenses, often called the "blind button".
I too have heard that its intended purpose is to allow easy mounting of lenses by feel.

Chris


Last edited by ChrisPlatt; 07-05-2011 at 04:17 PM.
06-19-2011, 09:30 AM   #5
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Thanks- that makes sense! I go in a dark room now and practice..
06-19-2011, 10:19 AM   #6
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QuoteOriginally posted by CarbonR Quote
My guess is that is a help to mount the lens on a body in the total darkness : look at the red point, if you align the pimple and the button to release the lens (when it's on the body), the red point will be aligned with the red point of the body
That's exactly what it's for, I remember reading that somewhere about 100 years ago.
06-19-2011, 12:41 PM   #7
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"Total darkness"? Say, what is the best lens for something you can't see or photograph?

The blind button might prove useful for example when switching lenses
at waist level while you continue to watch your subject,
or discreetly inside your camera bag so as not to attract undue attention,
or simply as a tactile aid in subdued light or for poor eyesight.

Chris
06-19-2011, 01:13 PM   #8
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I have seen it listed in books such as Carl Shipman as the Lens Mount Guide-Bump. Its function is to "feel" for proper alignment when changing lenses. Doing it in the dark has nothing to do with it, low light maybe. The were actually visible on the "k", M, and A series. They are black on the F series which was the last to have them.

Edit: Actually, I just realized that the FA 31 and 77 Ltd have a green bump and the 43 does not. The regular FA lenses had none and I don't think the FA* had them either .


Last edited by Blue; 06-21-2011 at 08:43 PM.
06-19-2011, 03:50 PM   #9
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I always thought the "pimple" was a guide on location and orientation. After you change it enough times you know pimple unlocked should be xx degrees from the top of body when locked it will be rotated xx degrees. Never really looked into the actual function of the thing other than a placement for myself.
06-19-2011, 10:06 PM   #10
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Yes, it's an alignment aid for mounting lenses on a Pentax film SLR. Don't use it for a modern Pentax DSLR, because the lens release button isn't in quite the same place as the lever on the old cameras...
06-20-2011, 05:13 AM   #11
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That is interesting! I have an A50/1.7 and have wondered what that bump was for. Thanks!
06-21-2011, 03:15 PM   #12
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Why was the bump discontinued
06-21-2011, 04:20 PM   #13
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QuoteOriginally posted by selar Quote
Why was the bump discontinued
Cost saving measure I guess.
06-21-2011, 04:34 PM   #14
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QuoteOriginally posted by selar Quote
Why was the bump discontinued
I think it's cause of what someone mentioned: at some point the lens release lever stopped being in a uniform place, but I still would probably like them. (I think they're still on at least the FA limiteds, or some of them. ) I sort of use the 'a' setting release to find my place: the aperture ring's usually set there anyway.
06-21-2011, 08:43 PM   #15
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QuoteOriginally posted by Ratmagiclady Quote
I think it's cause of what someone mentioned: at some point the lens release lever stopped being in a uniform place, but I still would probably like them. (I think they're still on at least the FA limiteds, or some of them. ) I sort of use the 'a' setting release to find my place: the aperture ring's usually set there anyway.
They are on the FA 31 and 77 Ltd's, they are green. The FA 43 Ltd did not get them which is weird since it was the first of that series. The regular FA don't have them and I don't think the FA* do either.
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