Wrote Thomas Horgan:
>Maybe some of the experts on this group could define sharpness or
>give some examples of sharpness in print photographs -- did you
>ever see the white line at the horizon in a landscape photo?
A) Sharpness in the plane of focus in subject:
1) Resolution. Lines per inch or millimeter. A function of cameraman
(holding, tripod, good focusing), camera (film flatness,
adjustment and
focusing aids in finder), lens quality and film emulsion (coarse
grain =
low resolution).
2) Acutance or edge sharpness. The abruptness of change from dark to light
or from one color to another at a subject edge. Mainly a function
of the
emulsion (thin = better) but can be influenced by development,
e.g. in
a dilute developer with still periods between agitations--but it
presupposes
good resolution in the first place!
3) Contrast transfer (MTF): does fine detail hold contrast or does it
go flat?
This is mainly a question of lens quality (if 1 and 2 are present).
B) Experienced or subjective sharpness. Heavy stopping down can create an
impression of great sharpness because more is in reasonable
focus--but
sharpness in plane of best focus decreases beyond mid-stops
because of
increased diffraction around edges of diaphragm blades. Also,
high contrast
subjects and contrasty printing can give rise to a false
impression of
sharpness. And coarse and sharp grain can mask an inherently somewhat
unsharp optical image, as I pointed out previously.
Each point above could be the subject of a chapter in a book---or even a whole
book! However, if we try to be clear about what we are talking about, much
misunderstanding will be cleared away.
Vänliga hälsningar/Best regards
Lars Bergquist
Välkommen till/Welcome to ...
<http://www.bahnhof.se/~timberwolf/>
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