Lens falling off the camera issue

[jto555]

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Have a look at this clip. If I touch the lens release button the lens rotates by itself in the mount. Now it is not locked onto the mount and will in time fall off. Two lenses on this body have the issue while two other lenses don't. On my second M240 body none of the lenses have this issue, it is only two lenses on the one body. What is making the lens move?

 

As one can imagine if I am covering an event for a day it is an easy issue to happen where I inadvertently touch the release button or clothing presses on the button. Ask me how I know...

 

 

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[Pieter12]

Time for service?

[jto555]

Yes, much cheaper than constantly repairing both lenses. I would like to know why it happens. 

[Pieter12]

1 hour ago, jto555 said:

Yes, much cheaper than constantly repairing both lenses. I would like to know why it happens. 

Seems like it might be a simple enough repair, since it is mechanical.

[Mute-on]

If you focus at infinity the cam on the lens is pushing the rangefinder roller arm inwards against a strong spring. It is possible that this spring is pushing the lens anti-clockwise and outward. I now store my lenses at closest focus on camera to reduce pressure against the spring tension. Most wouldn’t bother.

Dont press the lens release button unless you are holding the lens and about to remove it. I’ve never inadvertently pressed the lens release button since mine all require deliberate pressure. Unless yours has very little tension, I doubt there is anything wrong with the camera. 

Edited 8 hours ago by Mute-on

[adan]

10 hours ago, jto555 said:

If I touch the lens release button the lens rotates by itself in the mount. Now it is not locked onto the mount and will in time fall off.

Intriguing. There is no way any of my M lenses would do that on any of my M(10) bodies, without some force applied by hand.

I would check and manipulate the following, with the troublesome lenses off the camera but available for inspecting/testing themselves.

11 hours ago, jto555 said:

What is making the lens move?

The "rotary force" that is acting on the lens to make it "dismount" likely comes from the frameline-selection system (both the manual-selection lever on the front, and the internal connections to the viewfinder), which are spring-loaded.

The default "no lens mounted" position is for 135, 35, and 24mm lenses. Mounting 50/75 and 21/28/90 lenses applies force to move the FLs out of the default position, and hold them in another position to frame correctly with those lenses (well the 21 wouldn't actually be framing anything, but it will produce the same movement).

That force may be higher than normal for some reason, and therefore "kicking back," with the effect of pushing the lens counterclockwise towards disaster (should not happen). Try flipping the manual frame selector lever and see if it seems stiff or heavy to shift, when moving it back and forth.

50/75 lenses produce medium "kickback force" - 21/28/90 produce more kickback force. I am making an educated guess that the problem lenses are in those categories

However...

The camera's lens mount itself has pressure-springs to push the lens forward against the camera's mount-flanges from the inside when mounted - precisely to provide additional friction to mate the lens to the camera firmly, and prevent the lens from slipping counterclockwide to unmount without a hand turning it.

If the lens moves TOO easily when being mounted/unmounted, or wobbles even the slightest amount once clicked into place on the camera - those friction-producing springs may be worn out and too weak to do their job - i.e. press the lens flanges tightly against the camera flange.

Or the camera's flange surface may be worn or slippery.

Or the silver mount surface on the back of the lens(es) themselves may be worn down a bit or otherwise slippery (accumulated grease or metal dust).

Checking all those may at least give a hint as to what needs service.

[JohnW.]

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10 minutes ago, adan said:

both the manual-selection lever on the front,

The M240 is not fitted with a manual frame selection lever, so problem must be internal.