On Sun, 24 Jun 2001 at 15:05:17 +0530 (IST), Ayash Kanto Mukherjee
<[EMAIL PROTECTED]> wrote:
[macrophotography: shallow depth of field, long exposure times; will
a true macro lens help?]
The optical formulas relating depth of field to aperture, focal
length, and magnification are complex, but their implications are
pretty clear:
Depth of field at a given aperture is closely related to the
magnification factor. No matter what lens you use, you will have
shallow depth of field when you are working at near lifesize
imaging. There is simply no way around this: it arises from the
fundamental physics of the situation.
IOW, if you took photographs of the same scene with the same
magnification using a series of different lenses all set at the same
aperture, you would find little or no variation in the depth of
field.
A true macro lens will *not* overcome these limitations, but may
have other advantages such as a flat field of focus and optimization
for high resolution at close-up distances.
If you are seriously interested, I direct you to the following Kodak
publications:
N12A: Close-Up Photography (essentially up to 3x lifesize)
N12B: Photomacrography (3x to 50x lifesize)
N16: combined hardback edition of N12A & N12B
These were first published around 1969; I do not know if they are
still in print, but may be worth pursuing. I was lucky enough to find
a second hand copy of N16.
Note that these are *not* the last word on the subject, merely the
reference I happen to own; however, they seem to be extremely
thorough, and I doubt much has changed of a fundamental nature in 30
years.
--
Rodger Whitlock
Victoria, British Columbia, Canada
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