Focusing adjustment is too tight on field camera

[Ulophot]

Although the focusing on my Tachihara Hope is smooth when the lens is little extended, it grows tighter as it moves out, growing uncomfortably tight by the time I reach the area I'll be using most, about 8 1/2 to 10 inches of extension (with my 210). By uncomfortably tight, I mean that the I can turn the knurl but the movement is quite stiff and causes just enough jitter -- because of the friction, it jumps a bit rather than moving continuously -- to make fine focusing difficult as the image on the ground glass jiggles. It's not clear to me where the friction would tend to be and, therefore, what to try to do about it. There's probably an ordered series of things to try.

I am grateful, as always, for the voice of experience here.

[xkaes]

On my field camera, the locking/loosing knob is on the left and the focusing knob is on the right. If I don't loosen enough on the left, and focus too much on the right, the left will frequently tighten on its own. Then I just loosen the knob on the left a little more. Perhaps your camera works the same.

[Richard Wasserman]

Is the knob that locks the focus tightening at the same time you are extending the bed by any chance? I have had that happen on similar cameras.

[Richard Wasserman]

Darn, I need to type faster....

or

2 great minds and all that go with them

[Ulophot]

Gents, thank you both, but that is not the issue; the problem exists entirely independent of the looseness of the locking knob (which, indeed, is on the left). I got the camera used, this year -- my first field camera -- and have had to sort through a number of little issues with it to bring it up to par. I have not had sustained periods of days to work with it, so our making friends is taking a long time. Someone prior to me was, I think, a bit rough with it; possibly dropped it. There are friction plates on the back base for swing, and I'm going to need to figure out how to remove the rear standard and very gently flatten the upper plate on one side to make the back a bit more solid; the plate bows up very slightly, maybe a half-millimeter, just enough to allow some play when locked (the locking cam is centered).

Anyway, I am hoping that I don't need repair on the focus, just some proper lubrication or a fairly simple adjustment I can make myself. The budget for repair is out to lunch...

[Willie]

Might try taking the extension tracks off and lubricate them with silicone lubricant or with a good wax buffed well. Could be that on extension they put some pressure on the track they ride in.

[xkaes]

You need to carefully check to see if the bolt is bent. That might be very hard to determine. Try to loosen the nut on the RIGHT side. You might need to figure out how to keep the bolt from moving without damaging it. If the bolt or nut can't be moved, you have a problem. If you can loosen the nut, you might be OK. Just loosen it a little and see if that solves the problem. Locking it again is easy -- with LOCK-TITE.

[Ulophot]

I tried loosening the nut, as suggested, but that's not it. I got it all the way off with no change. silicone similarly did not help. I can't see anything in the motion that appears bent or "cam-like". I am beginning to assume that some of the wood along the track has swelled and will require sanding by a qualified technician, which will have to wait. Still open to other ideas.

[xkaes]

I'm out of ideas -- but I've been told that many times in my life. Good luck!

[LabRat]

The first thing to do is to obtain a machinist's square, but the adjustable sliding blade model from the home store (about $10) should be OK...

Check to see if all of the rail + bed are square to each other, then remove blade to use as a straight edge to check the sliding surfaces for bumps etc, then check to see how flat the bed + rail on the bottom + top... See if the glue joints are not loose on the rail or bed, and slightly changing angle/shape and enlarging when extended... Something may have swelled, expanded, warped, or some debris stuck there, too...

I think it might be something like the rail corners are not perfectly perpendicular, so a corner plane might be slightly larger than another, causing binding...

If you don't figure it out, or send to a camera tech, a local acoustic musical instrument tech should be able to find the bind...

Happy hunting!!!

Steve K

[mpirie]

Could this sticking be due to a change in local humidity causing the wood to swell?

I've had this on my Ebony and in fact, the manufacturer suggests a couple of strategic screws on the geared plate are slackened or tightened accordingly in the event of binding.

Rather than a silicone lubricant, i would suggest natural beeswax.

Mike

[Ulophot]

Thanks to all for your insights and suggestions. I'll do some more checking, but this is getting beyond my very limited engineering skills -- a term that would incite instant snickering in my dear family, who have seen the products of my skill many times. I'll probably have to save up, again, and send it to Richard Ritter, who knows from the inside how these things are built.
Just when I thought is was safe to go back in the... field.