Problems with Using Extension Tubes as Spacers

[Michael Erlewine]

In order to put my Nikon D810 on the BP-4 bellows or the Cambo Actus, I have to use a small extension tube in order to accommodate the MC-30 Remote Cord I use on my D810. I have tried both the PK-11a (8mm) and the PK-12 (14mm). Both lock in, but they wobble, the PK-11a wobbles less, but it is a danger to precise focusing, which side of the wobble it currently is shifted to. Is there any known way of making those extension tube rock solid?

[Bjørn Rørslett]

Such wobbling usually arises from either a worn-down and widened groove for the lens locking pin, or not sufficient pressure from the flexing metal strips that couple to the claws of the camera bayonet.  Inspect your extension rings and select the one with the least wear. The springy metal pieces can be pushed with a flat screwdriver or similar tool so they get increased curvature and therefore will lock with more force. Don't overdue this though, as the ring then can become hard to remove.

An old E2 or even M/M2 ring can be helpful as they tend to be little worn even purchased second hand and their bayonets usually sit much tighter. There is no aperture linkage through the bellows anyway so these old extensions will work just fine.

[benveniste]

I too think it's a matter of wear.  I use a no-name (Aputure) 12mm or 20mm extension tube as a spacer for my PB-4, and there's only a barely noticeable bit of play at the mount.  But break into a cold sweat if I think too hard about how much torque the PB-4 could accidentally put on the mount.

[Erik Lund]

I would not call it 'wear' - It takes thousands of hours of rotating the PK-Ring or a lens to start to show any wear on the lightly greased chrome where it is held against the mount, it does not wear like that. The materials of the mount are carefully chosen for the same reason.

On cameras with high usage, a lot of lens changes you can see the chrome starting to wear at this point but this has zero impact on how much the lens will wobble.

I would call it 'damage' due to 'rough treatment' while handling the lens-camera due to large sideways forces on the side of the lens/PK-Ring when mounted on the lens mount for instance while mounted on a tripod.

If the' wobble' is indeed like a 'Tilt' in a Tilt and Shift lens motion, see if it is between the lens and PK-Ring or the PK-Ring and camera to determine where the wobble is.

Also I have seen several PK-11A with loose screws in the mount this gives Tilt in the lens and PK-Ring connection. Easy to fix just tighten the screws.

What happens when tilting a 'non-tilt' lens is one of two depending on the design;

A - Steel spring design - All Nikon camera mounts and Nikon TC's
The steel spring is compressed fully and can loose the original shape and therefore loose the 'pre-tension' it was designed with.
Disassemble the camera mount or extension ring and recreate the original shape of the steel insert, callipers can be used easily to check the height of the curve of the spring.

B - Split bayonet tongues- Some Nikon extension rings and third party products.

As Bjørn states these can be 're-opened' with a small screwdriver,,,

[Michael Erlewine]

Good information Eric. I tried the E2 and other extension and there is varying wobble. Put in the M2 and it is perfect, so I will go with that.