Charles Krebs wrote: I think a key attribute of these would be the ability to get the "tube lens" diaphragm very close to the objective; something that is not easy to do with SLR lenses.
That is certainly a problem. One of the options I am considering is a 135mm f/2.8 Pentacon. The early "bokeh monster" version. I have the 200mm version and it's diaphragm is right out at the front. Zoom and the diaphragm moves out with the front lens. Coated but not multicoated. Amateur reviews show it to be sharp stopped down a little, but I have no certainty regarding corners.
I am also thinking of the 135mm f/3.5 Zeiss on the grounds that is has reviewed as very sharp corner to corner and wide open. As good as the best modern lenses. It has a very similar design to the Pentacon but diaphragm at the back. No real certainty that it will give such excellent results as a tube lens.
I have ordered a Morfanon, but god only knows how long all the adapters and extension tubes will take from China. Morfa showed it working well down to 160mm but it struggled a little at 120mm. Finite objectives are not usually happy run with seriously shortened tube lengths so I am just amazed it worked so well. Would the the "perfect" short tube lens do better? I figure it is worth trying.
Morfa added further confusion to the mix with the possibility that a thin lens might be the way to go. The morfanon is probably an example of trading a more primitive design against a better fit to the required characteristics, and now you are advising process lenses that trade the other way.
Arrrgggg. None of these options is demonstratively or clearly ether perfect or just the best available. Worse, there is no hope of any other solution than trial and error. I could also very likely be after something that just can't be done.