Loose screw on 55mm Micro-Nikkor f/3.5 Auto

[dslater]

I was looking at my 55mm Micro-Nikkor f/3.5 Auto when I noticed this screw that seems to be coming out. Before screwing it back in, I just wanted to verify that it's not supposed to be out like this and should be screwed in flush like the other 2 on the mount.

[dslater]

Actually, I just realized that's a picture of the M2 extension tube. However, the screw at the same position on the lens itself looks the same.

[beryllium10]

dslater,  The screw at the 180 degree position on the mount (bottom of the lens when attached to the camera) of my 55/3.5 protrudes like the one shown in your photo.  I suspect that means it's built that way (though possible that both our lenses are defective, I guess ...).  Your message title says "loose screw" - is it really loose?  I don't have a screwdriver handy small enough to check mine.

Cheers,  John

[Bjørn Rørslett]

This is the STOP screw.

Its presence is critically important. Without it being present, the lens can rotate further in the camera mount than the click-in position. If this should occur, the lens becomes jammed in the mount and can be very difficult indeed to remove. I have seen cases where the repair tech had to disassemble the camera to get the lens off again.

The morale here is: always check that a stop screw is present. It should not be 'loose', just sticking out and doing its job.

If the screw gets off and goes astray, most small screws can replace it. But the replacement should be of the kind with a tall head like the one shown in the photo of dslater's post. The main point is it should NEVER go flush to the surface.

When one does lens maintenance, it is advantageous to unscrew the stop screw and put some Loctite into the screw hole, then put the stop screw back and tighten it home. Some stop screws double in keeping the stray light baffle in position (always three small screws doing the job, one of which might be the stop screw). If that is the case, the Loctite should not be of the strongest bonding type otherwise you might have difficulties removing the rear baffle later.

[rosko]

I confirm that the same happens on mine.

There are 3 screws : 2 of them are flushing, only one protrudes. I assume the shape of the protruding one is different as the head is cylindrical while the others should be conical to fill the usual countersink holes.

[Bjørn Rørslett]

All F-mount lenses have stop screws. Never mount a lens or extension ring that lacks it.

[rosko]

Its presence is critically important. Without it being present, the lens can rotate further in the camera mount than the click-in position.

Ok. now I understand !

[beryllium10]

Yes, pondering it I checked and it's the same on all my other lenses.

[richardHaw]

the on my 16-35VR fell off (the head)
ruined by D7200 bayonet mount and aperture press lever. it broke my heart because the D7200 was less than 2 days with me

[Matthew Currie]

I've had one screw-loss incident, but was using a film camera, and could get the lens off by taking the back off and carefully manipulating the levers. One of my old Nikon F's had a bent aperture lever, pretty obviously from a similar incident,  but in those days at least, the lever was made of brass and I just bent it back.  Since that was about 30 years ago,  I guess it worked.

I'd hate to find out what kind of operation is required to do the same on a digital camera.

[dslater]

This is the STOP screw.

Its presence is critically important. Without it being present, the lens can rotate further in the camera mount than the click-in position. If this should occur, the lens becomes jammed in the mount and can be very difficult indeed to remove. I have seen cases where the repair tech had to disassemble the camera to get the lens off again.

The morale here is: always check that a stop screw is present. It should not be 'loose', just sticking out and doing its job.

If the screw gets off and goes astray, most small screws can replace it. But the replacement should be of the kind with a tall head like the one shown in the photo of dslater's post. The main point is it should NEVER go flush to the surface.

When one does lens maintenance, it is advantageous to unscrew the stop screw and put some Loctite into the screw hole, then put the stop screw back and tighten it home. Some stop screws double in keeping the stray light baffle in position (always three small screws doing the job, one of which might be the stop screw). If that is the case, the Loctite should not be of the strongest bonding type otherwise you might have difficulties removing the rear baffle later.

Thank you Bjørn for your explanation. As always, very helpful.

[Bjørn Rørslett]

...
I'd hate to find out what kind of operation is required to do the same on a digital camera.

I like to listen to the tall tales told by the repair techs concerning such cases .... Although stuck lenses are not common at all, they do generate problem-solving challenges for the poor technicians.

However, some years back, I discovered the problem myself. I had just CPU-modified a 35-200/3.5-4.5 Zoom-Nikkor and put it on a test camera (D2X I believe). The CPU apparently didn't work so I slightly twisted the lens to see if it made contact with the camera, and of course as the locking screw was poorly mounted it fell off and the lens went beyond the click-in position, it got stuck. Jammed real hard.

One could describe the process leading to the jamming as being reversible, but as experience shows, not in an easy manner. The unjamming took me about 6 hours of wiggling the lens back and worth until the lens mount suddenly became unstuck and I could remove the lens.

[rosko]

There is something else I am just aware now :

I have got a Zeiss sonnar 85mm f/2.8 for Contax Yashica  but F mount converted. I never could removed it from my Df without strive. For this reason I didn't dare to use it any more.
So, I just checked whether this screw was present...It was not !

I just swapped one from an old 43-86mm zoom and it fits and now my Zeiss sonnar is secure.

Thanks, the thread !