digital images

Alan Harvey aharvey at AMNH.ORG
Wed Aug 23 14:57:05 CDT 1995

Joseph Laferriere wrote:

>The problem is that the smaller the aperture, the longer the necessary
>exposure time. I once took a picture of the fruit of a Devil's claw
>(Proboscidea sp.) with a necessary depth of field of over 3 cm. The
>camera needed such a small aperature that it required a 60-second
>exposure. It came out beautifully. A video image is really a series of
>still photos shown in rapid sequence. The very nature of the medium
>prevents long exposure times.

Actually, the smaller the aperture, the less light reaches the medium per
unit time, which can be compensated for by either increasing the exposure
time OR increasing the intensity of the illumination.  E.g., in
photographing the Devil's claw fruit you could have gotten the same depth
of field with a more typical 1/60 -1/90th second exposure with a strong
enough flash (and without the color shifts due to reciprocity failure that
often result from very long exposures).  Still, still cameras probably are
more flexible than video cameras in both respects (exposure duration and
light intensity).  Does anyone out there know how to synchronize a
framegrabber/video system with a flash unit?



Alan W. Harvey (aharvey at
Assistant Curator of Invertebrates
American Museum of Natural History
Central Park West at 79th Street
New York, NY 10024
(212) 769-5638

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