Bob Frost wrote:
> Surely the whole purpose of collimated light sources is to achieve
> maximum
> resolution (I seem to remember this from my light microscopy days many
> years
> ago).
Actually, not really. You achieve higher contrast and higher apparent
sharpness at boundaries with collimated light, but if you equalise contrast
by other means, sharpness is pretty much identical.
I say 'pretty much' because there are some small-order interactions
between film grain edges and collimated light, which leads to enhanced
adjacency effects (an optical version of a sharpening filter). Diffuse
light bounces around more within the emulsion and tends to creep round
grain edges. However the optical ability of the lens system is unaffected
and a touch of USM should restore comparability.
What's more of a problem is the existence of higher amplitude HF with
collimated light excites more grain aliasing through interaction with the
sensor Nyquist limit.
Regards
Tony Sleep -
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