[filmscanners] Re: SS4000 again

["Bob Frost" <bob@frost.name>]

Tony,

Thanks for bringing me up-to-date - I did say my 'knowledge' was of light
microscopy many years ago. ;)

Bob Frost.

----- Original Message -----
From: "Tony Sleep" <TonySleep@halftone.co.uk>


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.

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