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06-21-2015, 12:46 PM   #1
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Lens moves on K5 mount

Have just bought a tamron 70-200 2.8 and notice the lens / body rotate slightly when locked, this has an effect on exposure as the levers in the lens and body can be at slightly different angles. The camera thus sets a different aperture, up to 1/2 a stop. Any comments

06-21-2015, 02:07 PM   #2
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Interesting. I can see how this might happen. Can you provide a few examples showing the over/underexposure with intact exif?


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06-21-2015, 02:44 PM   #3
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QuoteOriginally posted by fdr1150 Quote
Have just bought a tamron 70-200 2.8 and notice the lens / body rotate slightly when locked, this has an effect on exposure as the levers in the lens and body can be at slightly different angles. The camera thus sets a different aperture, up to 1/2 a stop. Any comments
This is normal with heavier lenses (a very very slight movement), except for the underexposure part. Would love to see samples as well.

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06-21-2015, 04:52 PM   #4
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I have noticed over the years that on a few of my third party lenses like my Sigma 50-500, mainly the heavier ones as Adam states, they move slightly when locked on the mount. I have never noticed any effect on the exposure settings though, I will have to test that to see if that's the case.

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06-21-2015, 06:40 PM   #5
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Yeah, my sigma 70-200mm and a borrowed 50-500 do move a bit. No more than one or two degrees rotation though, very small movement. Never had the exposure issues though, as others have said.
06-22-2015, 10:22 PM   #6
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Here are a couple of photos, I notice this only happens when the lens is stopped down not wide open at f2.8 , is this due to the small arc the aperture lever moves to set any given value the camera sets.
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06-24-2015, 09:56 AM   #7
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QuoteOriginally posted by fdr1150 Quote
Here are a couple of photos, I notice this only happens when the lens is stopped down not wide open at f2.8 , is this due to the small arc the aperture lever moves to set any given value the camera sets.
I was aware that this sort of variation based on the lens rotation on the mount is possible, but never saw it demonstrated. Fascinating.


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06-25-2015, 01:14 PM   #8
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If you look at the diameter of the locking pin in the camera body lens mount compared to the hole or slot in the lens, it obviously has to be small enough to fit easily. Some makes of lens do have a slightly larger hole/slot and this combined with variations in the fit of the bayonet will allow some lenses to rotate a bit.

06-25-2015, 01:32 PM   #9
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I measured the slot and pin with a digital caliper and the values where much the same if not closer than the kit lenses and my 300 f4. As has been said there will always be a very small rotation but the the angular movement of the aperture lever looks only to be about 10 deg so it does not take much rotation to give a 1 or 2 stop variation.
06-29-2015, 12:16 PM   #10
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I tried holding the on-off switch in the dof position while looking at the aperture blades and turning the lens in the mount, unfortunately, I couldn't see the blades move.
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