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03-15-2015, 11:21 AM   #1
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Pentax-FA 50 2.8 Macro - function of the clamp switch?

I have aquired a copy of this lens that works fine otherwise, but the clamp does not seem to do anything.
Since the lens operation is effectively stuck in one of the two possitions of the clamp - I'm trying to figure out if it is the "on" or "off" possition.
Information I could find online states that the clamp affects the resistance when turning the focus ring manually - for better manual focus experience.
As far as I can tell currently manual focus feels the same like other FA lenses that do not have a clamp - so my bet is it is in the "off" position.
Can someone that has a working copy of the lens comment ot the differences in operation between the two positions of the clamp?

03-15-2015, 12:18 PM   #2
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When the lens is vertically up or down the clamp, when on, increases the resistance on the focusing ring to prevent focus creeping away from the set position.

It works that way on my copy of the SMC Pentax-FA Macro 100mm f2.8 lens. The big brother of the 50mm.


03-15-2015, 12:32 PM   #3
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You should keep the clamp in the "off" position when using AF. On my copy of the lens, the clamp doesn't increase the resistance by much, but it does make a slight difference.

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