RE: Indoors film speed


Richard Knoppow (dickburk@ix.netcom.com)
Thu, 20 May 1999 18:34:52 -0700


At 07:41 PM 5/20/99 -0400, you wrote:
>
>> It may not be film speed at all that influences the final
>> negative density.
>> Many studio photographers using medium format equipment, without TTL
>> metering, have adapted and reduced their E.I. rating empirically to allow
>> for bellows/focus extension. This is explained in Gene Nocon's bbok on
>> Black and White printing.
>>
>> Cheers......Tony McLean.
>Dear Tony--
>
>
>I'm sorry to say that Gene Nocon couldn't be more wrong.
>
>1. Bellows factor does not change with light sources, only magnification.
>2. People take close-up photos outdoors.
>3. Unless you are working at extremely close distances or are using a view
>camera the bellows factor is negligible.
>
>If there is a difference in E.I. between tungsten and daylight sources, I
>shoot both and have never noticed, it must have to do with the film's
>greater sensitivity to the blue/green wavelengths.
>
>The only way to be sure is to run a film speed test measured on a
>densitometer. I have a student who owes me an extra credit assignment. I
>think I just figured out what her project is. I'll let you know what the
>results are.
>
>Jerry
>
>http://kmcamera.com
>
>
  Its really the difference between the spectral sensitivity of the film
and lightmeter. If they were identical there would be no difference in
required exposure index for any color of light.
  In the days of ASA speeds most lightmeters had selenium cells which have
relatively poor blue sensitivity. Modern meters use Cds or something else
which more nearly matches the film.
  In any case the error for pan film is less than is likely to be caused by
other factors such as shutter speed.
----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com



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