I've never used Velvia and, based on the examples from a MF friend, I
don't expect to.
However, I do have a comment about this 50 vs. 40 asa/iso discussion.
1/3 stop is into the range of variability to be expected in a
camera/lens/film/meter system. People without engineering/scientific
training and/or practical experience with electro/opti/mechanical
systems tend to assume that marked and labeled numbers represent greater
accuracy than is the case. There are manufacturing tolerances from
nominal values to be expected in each of these components. Age, wear and
time from adjustment simply make these bigger. They tend to average out
through the system, but there will be individual combinations that vary
from nominal by more than 1/3 stop.
To reliably get consistent results from film this sensitive to exposure
variation, one must, as Joel says, do one's own tests. If one uses
multiple bodies and lenses, multiple tests will be needed. If using an
all mechanical camera, tests of all shutter speeds should also be made
because of the way they are made and adjusted. Remembering that metering
is done wide open and that the mechanism that stops down to shooting
aperture is subject to error that may increase with wear and tear from
use, tests at all usual apertures may be useful as well. Anybody know
how much variation is effective speed there is between batches of film?
From beginning to end of batch? How consistent is processing?
I suspect that a fair amount of exposure variation that people blame on
their imperfect photographic skills are rather a result of thier
imperfect understanding and execution of extended system variable
management. Many years ago, I created and managed a small, specialized
production facility that made super hi-rez 4x5 transparencies including
both exposure and processing using a film requiring exposure accuracy of
1/4 stop or better for consistent results. Maybe that's why my favorite
films now are low contrast negs like Portra NC that are exceptionally
forgiving of exposure variations.
Moose
Joel Wilcox wrote:
<snip>
This is not the "proper" way to test film speed for one's taste and
one's camera. The proper way to do it is to set up a well-lit,
balanced scene with perhaps a white shirt and a gray card in it and
then shoot brackets using the ASA dial to change exposure. But when I
did that, I didn't find anything wrong with the ASA 50 setting. In
the field, I seem to get slightly different results. I think 40 must
be a little more accurate, since many people complain about the lack
of shadow detail with Velvia. Even so, a 1/3 stop difference is very
small!
In any case, no one should deviate from the manufacturer's
recommendations just because somebody on a list says to. He should do
his own tests.
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