Jeff Keller wrote:
Easy question - does the Sigma 600/8 use a T adapter or did they make
camera specific mounts?
Camera specific.
If the lens resolution is measured at the film plane image it's not
obvious to me why a longer lens would have a higher resolution.
I wasn't disagreeing with the published resolution numbers, just
pointing out how the standard tests aren't entirely relevant for some
super-tele photography. The standard tests reproduce the test chart at
the same size on film regardless of the focal length, the right way to
measure inherent resolving power. In using super-teles, I often find
that I can't magnify the subject to fill the frame from the vantage
point I have and can't move closer. In that case, there is no loss of
desired image coverage from using a longer lens, but the greater
magnification resolves greater detail in the subject.
Imagine a test target mounted on a wall across a canyon. A longer focal
length will resolve more detail simply because of the greater
magnification of the image on the film, assuming it's inherent resolving
power is at least the same as the shorter lens. With a 50mm lens you can
just see a white rectangle. With a 500mm lens, you can see the lines in
some of the larger (lower resolution) targets. With a 1000mm lens you
can see detail in the target for about twice the resolving power as
those that could be distinguished by the 500mm. It's not a resolving
power factor is the traditional sense, but has that effect through
different magnification a the particular kind of situation.
I don't know where else you can read about this idea, since I don't ever
remember reading about it. It's just an obvious effect of magnification
Moose
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