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08-21-2013, 09:35 AM   #1
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Manual lens yellow button

On a lot of manual lenses there is a yellow round button on the aperture ring, no...above the aperture ring. It doesn't seem to do anything when pressed. What exactly is it's purpose, and if it's missing, what affect will it have on the lens? I saw a lens on ebay claiming to be mint, yet the thing was missing.

08-21-2013, 09:45 AM   #2
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Its not a button but a marker to help you know how to orient the lens by touch to mount it on the camera.
08-21-2013, 10:49 AM   #3
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I have a Pentax M lens where this yellow button came off. The lens works perfectly without it.
08-21-2013, 11:18 AM   #4
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It's funny - that little button looks a lot like a white balance cap (you couldn't use it as such, but oddly similar design). But it's just a tactile point on the lens, nothing more.

08-21-2013, 11:45 AM   #5
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In the KX Manual, Pg. 6, it is called the "white plastic bump." Over time many of them have yellowed In some cases the bump was more yellowish or has fallen off. [CORRECTED per comments below]

3.
"In the dark, when the red dots are difficult to see, align the white plastic bump on the lens barrel with the lens release lever by touch, then turn and lock in as above."

Last edited by monochrome; 08-21-2013 at 04:30 PM.
08-21-2013, 11:48 AM   #6
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QuoteOriginally posted by monochrome Quote
In the KX Manual, Pg. 6, it is called the "white plastic bump." Over time many of them have yellowed or fallen off.

3.
"In the dark, when the red dots are difficult to see, align the white plastic bump on the lens barrel with the lens release lever by touch, then turn and lock in as above."
Some of the old ones are UV reactive so if you want to save your night vision you can use a UV flashlight and be able to pick up the dot (many of the red lines on older lenses were also UV reactive).
08-21-2013, 11:51 AM   #7
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QuoteOriginally posted by Docrwm Quote
Some of the old ones are UV reactive so if you want to save your night vision you can use a UV flashlight and be able to pick up the dot (many of the red lines on older lenses were also UV reactive).
So if I put an old lens with a yellowed white plastic bump in a south facing window for a week, will that clear the yellowing?
08-21-2013, 12:32 PM   #8
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Might be worth pointing out that the location of the lens release button has shifted upward slightly on some newer bodies, so the little lump doesn't quite line up with the lens release any more. On film bodies, the alignment is perfect.

08-21-2013, 12:40 PM   #9
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QuoteOriginally posted by Tanzer Quote
Might be worth pointing out that the location of the lens release button has shifted upward slightly on some newer bodies, so the little lump doesn't quite line up with the lens release any more. On film bodies, the alignment is perfect.
It does get you very close though and in the dark that is a big plus.
08-21-2013, 01:37 PM   #10
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QuoteOriginally posted by monochrome Quote
In the KX Manual, Pg. 6, it is called the "white plastic bump." Over time many of them have yellowed or fallen off.

3.
"In the dark, when the red dots are difficult to see, align the white plastic bump on the lens barrel with the lens release lever by touch, then turn and lock in as above."
If it's too dark to see your CAMERA, how are you going to take pictures? Was there an SMC-A 50/0.05 that I missed? (Imagine that... the front element would be something on the order of a meter across!)

Last edited by thornburg; 08-21-2013 at 01:38 PM. Reason: spelling
08-21-2013, 03:06 PM   #11
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QuoteOriginally posted by Docrwm Quote
It does get you very close though and in the dark that is a big plus.
Cheers. I just wanted to make it clear, if the OP has a newer camera model and was wondering why it didn't line up exactly.

QuoteOriginally posted by thornburg Quote
If it's too dark to see your CAMERA, how are you going to take pictures? Was there an SMC-A 50/0.05 that I missed? (Imagine that... the front element would be something on the order of a meter across!)
When shooting film, it is common practice to mount/unmount lenses in a dark environment to keep out excess light.

Probably a bigger reason to change lenses in a bag, by feel, is to keep out dust, such as when you want to change lenses at the beach. This would apply to any interchangeable-lens camera,
08-21-2013, 03:27 PM   #12
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QuoteOriginally posted by Tanzer Quote
When shooting film, it is common practice to mount/unmount lenses in a dark environment to keep out excess light.

Probably a bigger reason to change lenses in a bag, by feel, is to keep out dust, such as when you want to change lenses at the beach. This would apply to any interchangeable-lens camera,
Eek!



You keep my lenses away from the sand, whether they're mounted to a camera or not.
08-21-2013, 03:32 PM   #13
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@monochrome
QuoteQuote:
So if I put an old lens with a yellowed white plastic bump in a south facing window for a week, will that clear the yellowing?
Back in the beginning of the eighties, I bought several M and A lenses (used, but none of them very old). Some of them had a white bump, some a yellow one.

So I always thought their original color can be white or yellow, and it just marks different lens lines. But I never tried to investigate. Both of them made changing lenses in the dark much easier.
08-21-2013, 04:02 PM   #14
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As above I have seeral M and A series lenses. The colour of the alignment pip hasn't changed over time in my experience. Not really an issue in any case. It will serve it's alignment function no matter what the colour.

Tom G
08-21-2013, 07:06 PM   #15
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QuoteOriginally posted by Tanzer Quote

When shooting film, it is common practice to mount/unmount lenses in a dark environment to keep out excess light.
It's not a common practice at all- and is completely pointless. In an SLR, the shutter keeps light from reaching the film when you change lenses. If the shutter is damaged you will have a light leak whenever you take the lens cap off, whether you change lenses or not.
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