Effective speed of Delta

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Is it true that the effective speed of Delta is slower than the speed stated on the box? If so, why is that? And what should I rate with Delta 400? I use Ilford a lot about ten years ago and get frustrated with the speed, it was "a lot" too slow than recommended. Do Tmax400 have the same problem?

-- Kevin On Man Lee (kevin.o.m.lee@bc.sympatico.ca), December 18, 1997


You really have to experiment to find the EI that works for your equipment and shooting/developing style. FWIW I get the rated speed with Delta 100 and 400 developed in Xtol diluted 1:3 about 10% longer than Kodak recommends and printed with a dichroic (diffuse) enlarger.

-- Tim Brown (brownt@ase.com), December 18, 1997.

Effective speed

The effective speed of film is the point on the film curve where density reaches 0.1 (density units) above the density of film base and (normally occurring) fog. Because shadow areas develop out very quickly, the particular developer used makes no difference. 0.1>B+F is Zone I in the zone system. This is usually one half to one full stop slower than the manufactures' rating. If you lack access to a transmission densitometer, you'll be safe to divide the speed by 2 and set your meter accordingly. Make sure your shutter is calibrated accurately. There are proceedures for arriving at your personal film speed and development times clearly documented in Ansel Adams book The Negative and in Fred Picker's book The Zone System Workshop.

-- Michael D Fraer (mdfraser@earthlink.net), December 18, 1997.

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