Quote Originally Posted by leon bren View Post
Thanks for that and I think the answer is in your reply. I had a solid look into the works (as far as I could without disassembling the machine) and it all looks fine, but the bottom diffuser is, I think, not original. You note that yours has concentric circles - I bet it is a fresnel surface built into the diffuser to give the light box a focussing capacity in the same way that a condenser is focussed ( I seem to recall that tlr cameras often had a fresnel under the ground glass to brighten up the image too). I'll get a light meter and compare it with yours, but the use of a fresnel would certainly be logical and would concentrate the light. I'll work on that thesis for the moment.

Leon
I went to the $2 shop and bought a plastic "magnifying sheet" (aka fresnel) and cut it to fit onto the bottom of the light mixing box. That made things better but the diffuser was still losing too much light. I replaced it with tracing paper (remember that?) and the fresnel/$2 magnifying sheet and it gives a uniform light and has increased the speed down to 20-30 seconds at stop 11 for an 8x10 print. I guess that the old diffuser had cracked and been replaced with a heavier and non-focussing one. Still playing around with it for negative sizes other than 4x5 but it has certainly made it useable. I should add that it is a lovely enlarger to use.

Cheers and thanks