Focus problem

[Emilro]

Hi, I wanted to ask you guys a question, I have a beseler 23cII enlarger and it happens to me that it loses focus all the time. Is it a problem that the negative is heating up or is it something mechanical in the focus adjustment mechanism? I don't have heat absorbing glass by the way. Best regards

 

[Nicholas Lindan]

... negative is heating up or is it something mechanical ...

Yes.

If it is negative heating then the focus will change rapidly and then stabilize. If the image becomes defocused and then goes back into focus after a period of cool down then the problem is negative popping.

If it is mechanical then the change will be gradual and may continue for a while and will not recover if the enlarger is allowed to cool back down.

 

[@DrHSTGonzo]

I had the same issue a while back with my 23c, the heat absorbing glass helped a lot with negative popping. I also had to align the baseboard and head by adjusting the bottom bolt on the head assembly using a level. This helped me quite a bit making sure everything was in line.
https://conradhoffman.com/photo01.htm

 

[logan2z]

^ What they said, negative popoing is the likely culprit. I had the same problem when using my 23C II, even with the heat absorbing glass. I bought an anti-Newton glass negative carrier and haven't had the problem since.