On Sun, 1 Jul 2001 04:51:48 EDT (RogerMillerPhoto@aol.com) wrote:
> Film speed is determined by methods established by
> standards organizations; it's not up to the whim of an individual film
True, it imposes a standard means of comparison and to that extent is
perfectly fine. But the method of ISO measurement has been widely
criticised for using the wrong part of the sensitometric curve (ISTR
density 0.6 above base fog, or something like that). The value used is
barely off the toe of most films and not in the linear midrange. So quoted
speeds don't necessarily correlate with real ISO required for 'correct'
exposure of the 18% grey used for exposure meter calibration, but do allow
manufacturers to often flatter their products a fair bit.
http://www.halftone.co.uk - Online portfolio & exhibit; + film scanner
info & comparisons