Depth of field and enlarging lenses

[Richard Boulware]

Eugene et al: JP originally asked the question about Leica enlargers, and we, as good buddies, answered. Perhaps to Minox shooters, 35mm or 2 1/4 X 3 1/4 (Focomat IIC) IS large format. Why don't we all just mellow out on this one. Kind wishes, Richard.

[Brian Ellis]

There are many alignment tools available, all do a pretty good job but the Beseler one you have is among the worst. I had one for a while about seven years ago. As I recall, there is some fairly fundamental problem in using it. Perhaps it's that you can't see one or both bubbles while the tool is in the negative stage? Or maybe it's that you can't perform the alignment with the tool in place, so that you have to keep removing it and putting it back, removing a putting it back, until you finally guess right? I forget the exact problem but whatever it was, it caused me to use the thing once and then I tossed it in as a freebie when I sold my color head. I now use a simple adjustable level sold by Delta for about $15. I've always found the problem to be not with reading what a tool is telling me but rather with making the adjustments once I've used the tool. This is particularly a concern with the older Beseler 4x5s. The later version of the MXTs were changed so that it's easier to align the lens stage though other things are still difficult.

I don't know the answer to your depth of field question. However, enlarger lenses suffer from diffraction just like camera lenses so you don't want to be in a position of having to stop down below about two stops from wide open to gain even illumination.

[matthieu l.s.]

"uniform focus cannot be obtained without stopping down the lens"

This common observation (ideally made using a PEAK 2000 grain focuser which allows to see the corners) may reflect two very different situations:

1) the four corners are not focused together; this is indeed a misalignment of the enlarger.

2) the four corners are focused together but, at the same time, the center is not in focus; this is field curvature of the lens and I observe it for all my enlarger lenses used wide open (usual six element lenses, I have no experience of "apo" lenses). It disappears when stopping down the lens (two stops).

[jmcd]

J.P. Mose,

The second item on this page (DELTA 1 Enlarger Alignment Lens Board for Beseler Enlargers) looks like the Zone VI lens stage alignment fixture referred to within this thread. I think I will try one. http://www.camerastore.com/dl_cat_J/-J20_exposure.html

John

[Michael Feldman]

It has been mentioned above that one may not want to stop down more than 2 stops in order to avoid diffraction limitation effects. That may (or may not) be true, but the actual MTF charts for 150mm f/4 APO Componon-HM lens show that 2 stops down (f/8) is much better than 1 stop, and it is possible that 2.5 or 3 stops are just as good or slightly better. Unfortunately, the smallest aperture opening shown on the charts is 2 stops closed at f/8. These test charts referenced below are inclusive of diffraction limitation effects.

http://www.schneideroptics.com/photography/photo_enlarging/apo- componon_hm/pdf/apo-componon_40_150.pdf (Please remove any spaces in the web reference that were inserted by the forum software).

My understanding is that the APO Rodagon lenses are optimized for use at about 1 ? 1.5 stops closed, which does not appear to be the case for the APO Componon-HM lenses.