"You'll find that it's possible (common, actually) for a lower resolution lens to be sharper than a higher resolution lens." Paul I actually just don't believe that this applies to modern LF optics (which after all is what we are discussing here) - please can you provide some examples or some source material I can go and have a look at.
Also:
"Which is why a lens that produces high modulation (contrast) at 5-6 lp/mm (print resolution) but that has a low maximum resolution will appear much sharper than one that resolves many more lines per milimeter, but has lower modulation at 5-6 lp/mm." Can you explain this a little more clearly - Are we talking about contact printing here, or are we making some very huge assumptions about enlargment size. Once again, I've yet to see a modern LF optic which produces low modulation at print resolution (I'm presuming contact print - so no enlargement factor) but whose resolving ability is very high. My experience and (just about everyone else's too) seems to indicate that they are all practically indentical at print resolution (which is just a nothing sort of measure when no enlargement factor is used). I cannot believe that any modern lens is going to appear "much sharper" than any other at print resolution.
I recently tested 10 modern 150mm lenses to answer my curiosity around which lens would be most suitable for my puposes. I shoot architecture and some landscapes - color and black and white. I was interested in which lens would produce the best print (so there are a whole lot of variables in there). Percieved sharpness and tonal graduations are probably the key factors. Perceived sharpness includes modulation and resolution in a very "layman" kind of way. I shot a test chart and a real world 3-D subject (subject in both B&W and color). I'm aware of the limitations of the test chart. I was going to follow Norman Koren's methodology, but rightly figured that for what I wanted to deduce, the real world subject supported by the test chart would tell me all I needed to know. What did suprise me is that the test target (just the rez bars from the USAF chart shot centrally and with an edge target in the frame) actually produced the same results as the real world subject across the board. Were there significant differences: not really - one of the 10 was quite weak (I'm guessing it was a bit of a lemon lens). The rest would all have produced results which were not discernable in B&W prints under close examination below a 6X enlargement (24X30 from a 4X5 negative). To split hairs on the top 5, you would need very big enlargements (over 10X). Basically, this really validated Kerry and Chris' testing for me in a real sense - what is contained therein needs understanding in it's application, but it is an extremely useful resource, even for the completely uninformed and ignorant. Anyone not wishing to spend a lot of time testing or being geeky would be very well served to just blindly follow the results - and spend that time making photographs instead.
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