At 01:27 PM 11/17/04, you wrote:
>As a total tube rookie, and a very inexperienced macro photographer, is
>there a reason why I can't/should use my 100/2.8 + tubes for macro shots? I
>like the idea of the working distance that this setup would give, but have
>never tried it.
>
>Thanks,
>Evan
None at all. The working distance and extension required for a given
magnification level on film is related to focal length. Longer focal
length allows farther standoff for the same magnification level on film . .
. but it also requires more extension to get that magnification. I've used
tubes with everything from the 18mm/3.5 (you can only use the 7mm OM with
this lens . . . anything longer puts focus distance somewhere inside the
lens) to the 200/4. I've considered lenses longer than that to be more
weight (and torque) mechanically on the mountings than preferable . . .
plus something like the 300/4.5 would require an enormous amount of
extension to get the same magnification as with the 200mm.
I won't go into the math in this posting . . . it would be a bit
lengthy. A number of on-line resources have the math (do a Google) plus
Ansel Adams' "The Camera" has a section on it (just remember his discussion
is for view cameras and his total extension is from film plane to rear lens
node, approximately the lens board, not to rear focal point at infinity
focus, which is what 35mm and medium format commonly consider to be
"extension" . . . additional extension beyond focal length).
-- John Lind
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