Beseler 23c focus slipping

[kipkeston]

Hi. I've noticed a focus problem with my 23c II. I've done a search and I found one thread discussing it the problem and my situation is likely similar.

This is for 35mm. I start by focusing at f/2.8. I stop down to f/8 and check the focus. The grain is sharp. After a minute or two if I recheck the focus at f/8, it's slightly out of focus. My 23c II has the heat absorbing glass in it.

The possible causes I think are

1) heat reaching the negative
2) the mechanics are slipping causing this problem

Any other ideas? If it is a mechanical problem, is there a way to fix this on my own?

[Jon Shiu]

Perhaps check if it the neg popping due to heat. Devise an experiment where you check it the focus after having the light on 1-2 minutes, compare with another check of focusing quickly and then leaving the light off for a few minutes and then checking the focus quickly. If it's due to heat rather than slippage, you can get a Anti-Newton Ring glass from a gepe slide, smooth the edges with sandpaper and place this on top of the negative (inside the neg carrier).

Jon

[ic-racer]

I heat it up until it pops, then put the lens cap on and put the paper in the easel. Then I swiftly and smoothly turn the lamp off, remove the lenscap and start the timer.

There are a number of other solutions also.

[Whiteymorange]

The 23c series has a couple of delrin cogs that control the hight adjustment and those go over time, but I haven't had the focus shift on our (12) 23c's in a dozen years or so of working with them. If the proper 75 watt bulb is in the top, I have not found much of a problem with negative popping either. In fact, my students are often anything but prompt in their process and they still have few problems with heat. These are somewhat elderly mechanical beasts, so my first thought is that some nut somewhere needs snugging up a bit.

[resummerfield]

I had a similar problem with my 23C, using a glass-less negative carrier.

The heat from the lamp caused my negative to slightly flex, thus changing focus. I also installed a heat-absorbing glass, but it didn't cure the problem.

Try using a glass neg carrier.... that solved my problem.

[Trond]

I would guess, as others have in this thread, that the glass-less carrier is to blame. Glass on top of the negative is usually enough.

[John Koehrer]

There's a tension adjustment on both the focus and condensers. It's on the back, right behind the head. As I recall there's a plate that pops off, two springs and four screws. Add a little tension to the springs by tightening them 1/2-1/4 turn or add some tension by putting some shim stock between the shaft & spring(epoxy).