<<Extension tubes do degrade the image... Many lenses, for instance,
develop substantial field curvature when extended.>>
...
<If I did more closeup or macro I would certainly consider a macro lens. I
assume that the curvature development would also pertain to bellows...>
I think we get carried away sometimes. Lenses are tested on flat objects.
Unless you're copying slides or stamps or something, when was the last time
YOU photographed a flat object at macro range! In fact, a curved field can
be used to advantage when shooting the inside of a flower, for example!
My dad took prize-winning macro shots in the '50s by hand-holding a 4"
magnifying glass in front of his Praktika SLR! Don't let equipment get in
the way of creativity!
Please, don't take this as a flame against those explaining things -- it is
useful to know the capabilities and limitations of your equipment, but
sometimes we (I!) forget that we're in photography to make images, not
spend money.
Here's an exercise for those who want to do macro, but don't have a macro
lens. Take a bit of aluminum foil. Stretch it across the top of a ketchup
bottle and secure with a rubber band. Use your close-up filters, bellows,
tubes, or whatever, to fill the frame with the circle of foil, then focus
on the edges. With a finger, gently deform the center of the foil inwards a
bit at a time until it is in focus at the center AND the edges. If you're
truly meticulous, you can measure the deformation with a depth gauge.
Now you've characterized your lens, and know what kind of curvature you are
dealing with. Just as someone with a $900 macro lens learns to set up shots
to best use a flat field, you can now go and seek out (or contrive) macro
situations that exploit this sort of curvature! ("Just how did he get both
the center and the edges of that flower so sharp?")
: Jan Steinman <mailto:jans@xxxxxxxxxxx>
: 19280 Rydman Court, West Linn, OR 97068-1331 USA
: +1.503.635.3229
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