In a message dated 00-03-22 20:33:18 EST, you write:
> So, my question is: what does the letters Ipm stands for? I understand that
> it
> is the resolution of the lens but 37 to 47, is it good?
>
> Thanks!
"lpm" means "lines per millimeter" but I am in conflict over this definition
and would ask fellow list members for help. I had been taught 30 years ago
that :"lpm" meant line pairs per millimeter on the test chart. When you are
looking at resolution tests and the grain of the film interferes and
sometimes creates random patterns of what might be considered lines, I was
always taught that you have to look at 2 line pairs or a pattern of black,
white, black, white to be able to say that a lens resolves those lines.
However, on the web, I note that most people refer to "lpm" to mean one black
and one white line. So, my answer is I don't know for sure.
As to 37 to 47 lpm, this result is average or below average. Modern
Photography, when it was being published, had a sliding scale of sharpness,
with lowered requirements for telephotos and for the two stops at the
extremes of each lens' aperture range. By this, they described the Vivitar as
acceptable to good but also noted high contrast. But by modern standards,
this lens would rank average or slightly below. You should be able to get a
sharp 10 X 8 photo out of it though.
Warren
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