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12-15-2014, 09:03 AM   #1
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Join Date: Dec 2014
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Pentax 645 120mm macro lens will mount on 645N but not on 645NII

Hello guys.

I wonder if someone could help me with this or has any info, because I searched a lot, and couldn't find anything similar to what I am experiencing.

I have been using a medium-format film Pentax 645N with a manual 120mm F4 macro lens without a problem.

I wanted to try it with a 645NII body for the mirror-lockup feature, but the lens wont lock in the bayonet mount.

On the 645N, I simply twist it and it locks, easily, securely and every time. But I already tried two different 645NII bodies and on both the 120mm macro lens, so twisting the aperture ring twists the lens off.

Here is a video:

It occurs only with my 120mm F4 macro, which is a manual -A 645 lens. My other -AF 645 lenses 75/2.8, 45-85/4.5 and 150/2.8 lock fine.

12-15-2014, 04:19 PM   #2
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Location: East central Indiana
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The only thing I can think of is the locking pin on the 645mkII has a shorter locking pin and the locking slot on the lens is worn.

It could also be the lens mount is tight and when you feel the lens should be in the locked position, the lens might need to be turned another mm or two. My father had a Nikon D90 like that. One of his lenses would not lock into place correctly and would not talk to the camera. Had to remove and replace the lens onto the camera a couple of times to get it to lock on right.
12-15-2014, 05:47 PM   #3
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Join Date: Dec 2014
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Original Poster
Thank you for the suggestion.

I will try to measure it tomorrow and take some macros of the locking parts to spot something like that.

Since I am still new to the 645 system, I firstly wanted to rule out if it is an official incompatibility (but then it should have been in the manual) or a minor defect in the body or the lens.

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120mm, 120mm f/4 macro, 120mm macro lens, 645n, 645nii, camera, f4, lens, lens mount problem, macro, pentax, pentax 645 120mm, pentax help, photography, troubleshooting
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