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Re: [OM] Velvia at ASA 40

Subject: Re: [OM] Velvia at ASA 40
From: Moose <olymoose@xxxxxxxxxxxxx>
Date: Sat, 22 Feb 2003 12:41:28 -0800
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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