OM bellows slipping

PanoGuy · Post by **PanoGuy** » Sat Jun 26, 2010 1:29 pm

Anyone ever have trouble with the rear mount (i.e. where the camera attaches to the bellows) slipping? Even when the knob is tightened completely the rear mount will slip slowly downward when vertically oriented.

I disassembled the knob and verified both the screw-knob and its screw-in socket are as tight as they can be. After trying to switch the screw-in knob with the one from the front mount the problem remains.

Maybe the best idea is to add some type of small padding under the screw to increase the pressure applied? Any better ideas or results from past experience?

enricosavazzi · Post by **enricosavazzi** » Sat Jun 26, 2010 1:43 pm

The Olympus OM bellows have the usual nylon dovetails of many SLR bellows, and a fairly smooth prismatic rail. This type of bellows simply does not lock completely, even when the locking thumbscrews are tightened very had (too hard, in fact). I did have the same problem with OM bellows, which perhaps are slightly more prone to creep than other bellows, but the Nikon PB-6 are not much better.

I am afraid I don't have a solution. Overtightening is likely to break or wear down something in the long run. The tip of the thumbscrew presses the nylon against the rail (possibly there is a small metal disc between screw tip and nylon). Adding some padding at the end of the screw is not likely to improve things, unless the nylon dovetail has worn down and the tip of the thumbscrew fails to apply pressure to the nylon at the bottom of its hole - in this case a 2.5 mm steel ball or 2.5 mm short metal cylinder dropped into the screw hole might make things better.

rjlittlefield · Post by **rjlittlefield** » Sat Jun 26, 2010 2:45 pm

Try cutting a small strip of aluminum foil and slipping it between the nylon and the rail. Fold the ends of the foil up against the nylon and tape it in place so it doesn't slip out when moving the bellows.

If there is enough space, try using a piece of paper or thin card stock instead of the aluminum foil.

What this approach tries to do is provide a shim or "facing" of material that is less slippery than the nylon and also will tighten down over a larger area than the nylon alone does.

As you can see HERE, the nylon parts sometimes have to be bent quite a bit in order to press against the rail. The resulting tilt means that they may contact only along a narrow band. Filling up the gap with a thin sheet of something helps with the angles as well as the slipperiness.

--Rik

PanoGuy · Post by **PanoGuy** » Sat Jun 26, 2010 3:24 pm

The nylon is definitely bent as in Rik's link, but not to that extreme. Adding a piece of paper between the nylon and rail improves things, though not quite as much as I would like. Only a single piece of paper will fit currently, so I may try to set something up that will expand the nylon back into shape and then add the shim. This should bring much more of the rail into contact.

Thanks for the ideas.

Craig Gerard · Post by **Craig Gerard** » Sat Jun 26, 2010 6:08 pm

I'm not sure if this is applicable; but Charlie provided a link in another OM bellows related thread.

Nylon Blocks for OM Bellows:
http://www.zuiko.com/index_016.htm

Craig

PanoGuy · Post by **PanoGuy** » Sat Jun 26, 2010 7:16 pm

Thanks for the link Craig. The nylon pieces don't seem to be too far out of shape, it's just that they don't grip the rail well enough.

enricosavazzi · Post by **enricosavazzi** » Sun Jun 27, 2010 12:09 am

By the way, on the same side of the moving platform where the friction thumbscrew is located there are also two small set screws that press the nylon dovetail against the rail. To release the dovetail as much as possible from the rail you must unscrew these set screws by one or two turns.

Charles Krebs · Post by **Charles Krebs** » Wed Jun 30, 2010 5:47 pm

Panoguy,

On my Olympus bellows I have 0.01" brass shims "installed" on the nylon blocks on the side that is "pushed" to clamp. Essentially what Rik recommended. (I found this to be a surprising amount... you may need less). In order to do this it was necessary to "back off" fully the adjustment screws Enrico mentioned. The standards were slid off of the rail to insert these, otherwise there is no way I could have just slipped them in.

Before, it never tightened really well, and if I peered down the rail when it was "tightened", I could see "daylight" along most of the clamping surface... it only made contact at the very top edge. With the brass shims in place it locks down much tighter, and with less effort. It appears to be making contact with the rail along the full surface of the locking block. (I would think that this also would cause far less stress on the plastic block). The movement is snug, but very smooth.

PanoGuy · Post by **PanoGuy** » Wed Jun 30, 2010 6:39 pm

Charles,

Is this where your shims are placed?

There is not much of a gap in this area, but even when tightened down there seems to be very little pressure against the rail.

Also, how did you attach your shims?

Charles Krebs · Post by **Charles Krebs** » Wed Jun 30, 2010 8:21 pm

Yes. The shim covers the entire surface that contacts the rail on the clamping side. The pieces were cut a little oversize and the parts that extended past the ends of the block (a little less than 1/8 inch) were folded over as tightly as possible against the block. They stay in place quite well. But if they ever started shifting around too much I would probably use a small amount of cyanoacrylate adhesive to keep them in place. (Although I wouldn't do that until you were satisfied with "feel" of the modification, and shifting was perceived as a problem. I haven't had the need to do so.)