At 16:46 9/14/00 , BBB asked:
>Using the extension tubes with a normal (non-macro) lens, should I
>set focus to near or infinity for best results?
Assuming you are asking about primes, this may depend on the lens. If all
the lens focus helical does is extend the entire lens, it doesn't matter.
The lens must be extended the same distance from the film plane to focus at
a specific subject distance. Whether the extension from the film plane is
achieved with an extension tube or the focus helical doesn't matter. If
there is an internal floating element, which Olympus uses in some of the
fast wide-angle lenses (and I believe in the newer 85/2 also), one end or
the other of the focus helical may be friendlier to usage of extension
tubes. What you want generally for macro work is a very flat field free of
pincushion or barrel distortion.
>What affect will this
>have on actual depth of field?
None. For a particular focal length, your depth of field remains the same
for a specific focus distance, whether you achieve it using an extension
tube, or the focus helical.
-- John
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