>
> I'm still not grasping the correlation between f:Stops and density
> range.
OK. The reflectance of a scene is what governs camera exposure, and is
measured in stops. Transmissive density of a piece of film can also be
measured and expressed in stops, and if you use a suitable light meter you
could measure the EV for blank processed film and again for maximally
fogged film and be able to say that the density range = so many stops.
But it's more usual to express a measured transmissive density as a log
value, because 0 = completely clear, perfect transmission. With stops
there is no such reference value for zero opacity (you'd have to
reference it to a standardised lightsource luminance), and the calibration
anyway belongs to lens systems. Densitometers are thus calibrated in log
values, and each increment of 0.3 (log2=0.301) represents a halving or
doubling of transmitted light through the target.
So a real-world measurement of a piece of film might give a minimum
density (base fog + substrate) value of 0.2=Dmin, and a maximum opacity
(Dmax) of 3.8, in which case the OD (optical density) range = 3.6. You
could equally say there is a 12 stop range between the amount of light
transmitted at Dmin and that transmitted at DMax, but it'd be a mouthful:)
Regards
Tony Sleep
http://www.halftone.co.uk - Online portfolio & exhibit; + film scanner
info & comparisons
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