At 17:19 4/9/02, Ian Nichols wrote:
In article <000e01c1e012$3baf4560$34b51e3e@eric>,
Eric Boyce <ericboyce@xxxxxxxxxxxxxxxx> wrote:
> >I assume you know about reciprocity failure?
> the effects on film of exposures of longer than a few seconds?
Well, specifically that for long exposures halving the light intensity
(e.g. by stopping the aperture down a stop) requires more than a doubling
of exposure time.
If you haven't already discovered it, most film manufacturers have lots of
useful information on their web sites, including data sheets for their
films (usually in pdf format) that you can freely download and refer to.
They will tell you how much to compensate for a given indicated exposure
time.
Yes . . . the exposure time at which the reciprocity law "fails" varies
greatly from film to film. Furthermore, with color film the failure often
occurs at different long exposure times for each emulsion layer (the cyan,
magenta and yellow layers). Consequently, there are often filter
recommendations as well. With color negative the printer can often
correct, but with slides intended for projection (versus printing)
considering color correction becomes more important.
BTW, my **favorite** exposure meter of all time:
Imperial Exposure Meter
No. 1 For Bright Light
The Imperial Dry Plate Co. Ltd.
Cricklewood, London, N.W.
Patent No. 3873 - 1901
f-stops from f/4 through f/64
Shutter speeds from 60 seconds to 1/500th second
Folds up and fits in shirt pocket like as a very thin book. No
batteries! Smaller and thinner than the Kodak Master Photoguide. Uses an
"actinometer" that still works. Only *two* moving parts: the actinometer
paper and the "slide" that is held captive by a "stator" much like a slide
rule. What could be simpler than that?
If I could only find some Imperial Orthochrome:
Special Sensitive, Special Rapid, or Non Filter.
Any of the three would do. Any of our U.K. list member know where I might
get some?
Anyone got a conversion scale from H&D speed numbers to the ISO system? I
suppose I could create one from the "Sunny-16" rule.
-- John
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