Regarding post 15. If the lamp is on long enough during composing, focusing and then grain focusing, and the user focuses near the center of the image with the negative popped, the film will have bellied-up in the center, while leaving the edges clamped at a lower height. The outer edge areas don’t get nearly as warm, since the upper and lower plates of the negative carrier act as a heat sink. Such a popped negative cannot be projected with uniform focus.
In this case, when the exposure is made, the popped center will be in focus, while the rest of the negative falls out of focus radially, because the rest of the negative lies progressively below the plane of focus established about the popped center.
If, on the other hand, the center is focused quickly before the negative warms enough to pop, then when the relatively long exposure is made, the negative will pop leaving the edges in focus, but progressively out of focus towards the center. Recall that the original poster claimed f/22 to obtain longer printing time for burning & dodging.
Thus, a popped negative can produce a sharp center progressively blurred radially outward, or sharp outer areas with a blurred center, depending on how it was focused. Too, some workers have tried to compromise by focusing at a point midway form center to corner and then using a smaller-than-usual aperture in the hope that the increased depth of field will mask the problem.
Nothing works nearly as well as the following combination:
1. Use a HAG filter to remove as much heat as possible. This is not needed with a dichroic-filtered head, as it has its own heat-absorbing (or heat-reflecting) filter built-in.
2. Use a glass carrier.
“Junk Triplet” lens? Maybe not.
I have made many very good prints with the ubiquitous 50/3.5 and 75/3.5 Cooke Triplet enlarging lenses supplied by Marumi Optical Company and marked "JAPAN". The actual manufacturer is unknown. These are marked under many brandings (at least 54 per my count), but a close examination reveals that they are identical—almost certainly made by the same maker. I amused myself a few years ago by collecting the brandings.
I read many comments about these “crappy lenses”. By discussing these privately with folks that got prints that were sharp is some areas and fuzzy in others, I learned that most of them were acquired with a condenser enlarger without the benefit of a heat-absorbing filter or glass negative carrier. By listening to their tales of woe, I realized that I had the same terrible focus problems they did with a then newly-acquired Beseler 23CII.
I then got a Beseler 8042 heat-absorbing glass filter for the upper filter slot. This mostly cured the problem. I still got some somewhat unsharp areas with sufficiently-long printing times. This was worse with overly-dense negatives. I presume that denser negatives absorb more heat and tend to belly upward worse than a negative of more average density.
When I added a glass carrier the problem disappeared entirely. Now the “crappy triplet” produces nice prints with good definition. The common 3- or 4-element “beginners” lens often gets blamed for a problem having nothing to do with the lens.