Copystand connection sag reducing parallelism - can I use a threaded rod

[loccdor]

I have a Pentax Copystand II from the 70s. The connection between the arm and the fine-tune device seems to be a bit weak for the weight of the camera, causing it to pitch forward slightly, losing parallelism with the board. Everything's parallel until that connection.

It's as tightened as it can be.

I had an idea. Could I use a long threaded rod which is expandable by screw-motion, and have it contact the board as well as the camera near the nameplate, in order to pitch the camera up by a couple degrees? If this seems reasonable, what sort of parts would I need to search out for such a rod.

Or should I try a thin wedge shim inserted at the edge of the connection? Seems like it would be hard to get the angle right and keep it there.

Maybe there's a better solution I'm missing.

 

[koraks]

I have trouble visualizing what you mean.

Roughly speaking I'd see two ways to support the camera if the present bracket is insufficiently rigid:

The existing parts of your stand are in grey, the camera is the black shape suspended from it. Both red bits are the optional supports.

The vertical one would be a support that would make the setup very solid; I suspect this is what you're referring to. This might indeed involve some kind of threaded rod, although I doubt that's a very convenient option. A bar with a clamp of some sort seems more convenient.

The diagonal option offers an additional linkage towards the existing main column and should help avoid sag in the existing crossbar attachment. Again, some kind of clamping system seems the most appropriate.

Things will be easier if the camera is always at the same position e.g. for 'negative scanning' of the same format. If it needs to move, especially steplessly, it may be a bit more difficult to set this up, but it's still possible.

Implementation would also depend on whether you want to limit yourself to whatever you have in your parts bin vs. if you're willing to purchase or manufacture some additional hardware.

 

[loccdor]

Thanks @koraks for the thorough reply, if it helps it looks something like this in use:

Ignore that floating part in the middle.

So to accomplish your idea with the longer support you drew in red, I think I'd need some kind of long L-shaped bracket that the camera goes into with tripod mount, then then wraps around the back of it. I guess I could look at something in the vein of SmallRig camera cage type of parts.

The easy solution is to use the adjustable feet on my film holder to match the angle with the camera - works for single images - but this won't allow for clean stitched images when the negative is shifted.

 

[koraks]

Two more options; there are more possibilities.

Or of course use a stand that's stable to begin with and save yourself a lot of trouble. E.g. get a sturdy enlarger and remove the head, put the camera in place. That's what most people do.

Personally if I'd want this setup to work I'd put it in front of me and the parts bin next to it and start trying things out. This is one of those things you can spend hours on the drawing board with, but what it needs to do is work in practice with what you've got. At the level of theory you can only derive basic guidelines like "multiple support points as far apart as possible" etc. Those are OK as guiding principles but they're not actual solutions yet.

 

[Ian C]

Since this was made by Pentax, I assume that it was meant to bear the weight of a 35 mm SLR & lens. The plated column is likely a hollow tube of steel or aluminum. It seems to me that the assembly should be ridged enough to keep the lens axis sufficiently close to vertical, and therefore, perpendicular to the base board.

If the knob screw that fastens the arm to the vertical fine-adjustment unit has too little tension, you could remove knob screw and replace it with a strong socket head screw and whatever washers are needed to safely distribute the clamping force of the screw head against the casting.

Then you can tighten the socket head screw with an Allen wrench. This will make it easy to attain much greater clamping force between the arm and the vertical adjustments unit. That should give you a strong connection that keeps the two mating surfaces clamped.

It’s a good idea to apply grease to the threads of the screw before assembly to reduce thread-to-thread friction. In this way, more of the torque applied to the screw goes into generating clamping force between the parts. It also reduces wear of the female threads, which are likely aluminum alloy (relatively soft).

I presume (but don’t know for certain) that the screw is likely 1/4" x 20 threads per inch UNC, and therefore, readily available at a full-service hardware store in the US or Canada (requires a 3/16” Allen wrench).

 

[runswithsizzers]

Assuming you are not trying to mount a monster camera which greatly excedes what the stand is designed for, then...

The first thing I would try would be to insert a shim in the area I have marked in green. The shim could be several layers of card stock or pasteboard from a cereal box or matchbook cover.

If that does not provide enough correction, you could also insert a second shim where the column mounts to the base to tilt the column.

You might also try something like a bungee cord between the camera mounting part and the column to pull the camera back into vertical.

 

[loccdor]

@Ian C That's a lot of information I had not known or considered. Thank you. I'll have to give replacing that knob with a screw a try...

 

[loccdor]

Assuming you are not trying to mount a monster camera which greatly excedes what the stand is designed for, then...

Thanks for the ideas. Just about a pound over what would typically be used on it during the time period, I think. Should be alright.

 

[runswithsizzers]

I think the problem is fairly common to a lot of copy stands. The manufacturers design the parts as if there will be no "play" between the moving parts -- but moving parts always have some play. I think the threaded rod idea is going to be difficult to make and awkward in use, so I would try these lower-tech possibilities first:

 

[MattKing]

I like the bungee cord idea. A turnbuckle and a couple of rubber loops might work similarly.

 

[loccdor]

I'll give the bungie a try as a first step since it's cheap and easy. Maybe I can get the tension close enough that it doesn't cause a tilt in the opposite direction. Thanks everyone for your input.