At 08:47 PM 6/15/2001 +0000, you wrote:
>OK, did I miss something significant here, or did the subject just get
>changed? I'm *assuming* that "a resolution of 75 lp/mm" refers to 75 lines
>per milimeter--in which case the "/" is redundant. But of course, film has
>no lines per anything, it just "is". Measurable, of course, but any
>"lines" are artificial.
Someone else has already mentioned that lp = "line pairs".
Resolution is tested using special targets that contain sets of lines at
increasing density. The target is photographed (scanned, whatever) and the
result is evaluated. The set with the highest number of line pairs per
millimeter in which you can actually see that the lines are separate
determines your resolution. It is, of course, an artificial measurement, in
that, as you imply, an actual scene doesn't have "lines". That's why the
number is often referred to as the "theoretical resolution" of a lens,
camera, scanner, or whatever is being tested. It does have a relationship
to actual picture taking; you would expect a lens, say, that has a higher
theoretical resolution than another lens to actually take sharper
pictures--and it really does, all other things being equal. Of course, the
difference may be too small to see with the naked eye if the difference in
theoretical resolution is too small. That's because the eyeball also has a
theoretical resolution.
Stan
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Photography by Stan McQueen:
