----- Original Message -----
From: "Colin Talcroft" <ctalcroft@yahoo.com>
> I have rigged up an "extension tube" for my Zero image
> 4X5 camera that puts the pinhole 32.5CM from the film
> plane. The pinhole is designed for use at about 5.0CM.
> I'm not worried about the "optimal pinhole" thing. I'm
> confident this will create an image, just wondering
> how much this distance is likely to force me to
> lengthen my exposure time. I will be experimenting, of
> course, but in the hope of not wasting too much film,
> does anyone have a rule of thumb?
There is no "rule of thumb", just plain physics of light.
This case is in no way different than if you were using a glass lens.
> If I would expect a 2-second exposure outside in full
> sunlight with a 5.0CM "focal length", for example,
> what would be a theoretical equivalent at 32.5 CM?
84.5 seconds (uncorrected for reciprocity, time)
Guillermo
Received on Fri Nov 30 00:18:08 2001
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