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Long lenses, or telephotos, have always held a
fascination for all photographers. Not long ago, a study by a
national photo magazine showed that a telephoto lens was the
first ancillary purchase for new camera buyers.
We see fantastically long lenses on the
sidelines of sports arenas, on the beach at famous surf breaks,
and of course, those wonderful Alaskan cascades where salmon
appear to leap into bears' mouths to the click of a hundred
shutters.
35mm camera manufacturers long ago dubbed the
50mm lens as "normal" with telephotos beginning at 85mm and
extending out to 1000mm and beyond. The major trait of the
telephoto is it magnifies a scene. A 100mm lens will make a
scene twice as large as a normal lens - a 500mm lens will
magnify by a power of 10.
Long lenses also tend to magnify camera
movement. High shutter speeds and/or a tripod are recommended.
Other traits include a decreased depth of field, useful for
portraiture in throwing a background out of focus. Telephotos
also tend to flatten distance and compress objects in the scene,
a pleasing visual effect for many subjects.
Prosumer digital cameras generally come with
built-in optical zoom lenses that move from a wide angle view to
a moderate telephoto. A 3X zoom will generally range from 35mm
to 100mm providing a practical choice of focal lengths. The
Canon IS Pro90 has a long focal length of 370mm, really getting
out there. Canon's image stabilization system on the digital Pro
90 makes hand-held shooting at the longest focal length a
possibility.
Most digital cameras come with a
wonderful-sounding feature called digital zoom. Fortunately,
digital zoom can usually be disabled. The digital zoom feature
increases the apparent focal length of the lens by cropping from
the center of the image and - very important - decreasing the
resolution of the image.
However, for one group of enviable digital
shooters, the digital zoom can be extremely useful. I'm talking
about those who shoot exclusively for on-screen use: web and
multimedia.
Optical zoom @ 210mm
The pictures on this page were taken with a Fuji
6900Z which has a 6X optical zoom plus digital zoom for three
resolution levels: 3mp, 1mp and VGA. All four photos were taken
from the same vantage point, using a tripod and a high shutter
speed.
With just the optical zoom turned on and the
telephoto to 210mm, the 6mp image at top looks very sharp (until
it's been compressed for web use).
3mp @ 294mm digital zoom
Dropping the resolution to 3mp and using the
digital zoom runs the telephoto our to the equivalent of 294mm
and the image appears quite sharp, excellent for web use. Note
how the scene seems compressed with light poles appearing to
"stack up."
1mp @ 462mm digital zoom
At 1mp resolution, our lens has stretched to
462mm and the resulting image is still sharp enough for web use
but not fit to print.
And finally at VGA (640x480), the whopping focal
length of 924mm gives a fuzzy image not fit for anything.
VGA @ 924mm digital zoom
In short, if you're shooting for the web or
screen presentation only, don't be afraid to experiment with
your digital zoom. If you're shooting for print, digital zoom
should be used only in desperate times.
Next week, I'll try to cover the acres of PMA
2002 in Orlando and give you an update on digital cameras and
other equipment. |