Testing Film, was Re: Step Wedge

Whatever works for you is fine, but without wishing to sound to
negative about this method of testing it has some serious flaws, in
my opinion.

First, as mentioned in a previous message, flare is a serious
problem. If flare were consistent and predictable we could account
for it, but it is not. It varies considerably with bellows position,
lens, subject lighting, and type of lens hood used. And,
unfortunately, even small differences in flare will distort curves
significantly, so much so that the method makes comparison of
effective film speed of different films virtually useless.

Second, the accuracy of most shutter systems does not provide the
degree of precision necessary to compare different films and
determine EFS. You really need some type of light integration for
this.

I used the method suggested for many years, and it works fine for
some purposes, i.e. determining development time for a specific film
in a certain kind of lighting condition and with lenses of similar
transmission. The method seems very intuitive but it is inherently
flawed in many respects and is not a reliable way to determine either
SBR or EFS, or to compare the EFS of different films. The BTZS system
of testing, which eliminates most factors other than the
characteristics of the film material itself, is a much superior
method of testing.

Sandy King

> >>> dilcher@hiddenworld.net 11/10/04 1:24 PM >>>
>>>Is the 31-step wedge, mentioned, on a 4x5 piece of substrate? I was
>thinking sandwiching this in front of film, in my film holder, and
>exposing in-camera would also serve to help me conduct film tests...
>
>BTW, anyone use this method of generating film curves and finding
>film speeds? I'm assuming that I would be exposing an evenly
>illuminated
>surface at zone X? (snip)<<
>
>This method is described in John P. Schaeffer's "Ansel Adams Guide:
>Basic Techniques of Photography- Book 2" pp. 52-61.
>
>I've used it and found it to be very efficient and convenient.
>
>Joe
Received on Wed Nov 10 15:24:37 2004