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Check
out our...
RESOLUTION
CHART
TAMRON
AND TOKINA SQF CHARTS
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| Sample
jungle dilemma: The
Tokina 24-200mm f/3.5-5.6 ATX AF (left)
is considerably larger, and heavier, and
doesn't focus as close as the Tamron 28-200mm
f/3.8-5.6 XR AF but offers 4mm in wide angle.
But do the optical differences between them
count more? |
Whenever
anyone asks me how he can tell if his lens is
sufficiently sharp, I tell him (or her) to take
pictures with it. Load up with one of those great
ISO 400 slide films, wait for a nice bright day,
find a colorful scene at mid-distance, and shoot
away using a tripod.
Nothing
makes a photographer's heart beat faster (or
eyes sparkle more) than enjoying a well-exposed,
bright, crisp, trans-illuminated slide as revealed
through a 4X-or-greater magnifier.
Satisfied,
but still not sure how the lens performs at
full aperture or different focal lengths? Go
shoot and see.
Taking
pictures and enjoying them is what photography
is really about, so why not let your own pictures
settle the matter subjectively?
Surely
we can get more objective tests of lenses that
will help us quantify specifically whether lenses
are excellent, very good, good, fair, or not
acceptable. And surely some lenses may be rated
differently at various apertures, center, and
edge. Is lens A better than lens B, and what
about lens C?
So
at just about the birth of photography, the
search for a method to test lenses began. Optical
engineers—pseudo and qualified—stared
through optical benches atĘstar images
formed by lenses at infinity, detected aberrations,
and even read test targets. Dozens of lenses
could be examined swiftly.
Such
visual examination was challenged by other optical
engineers who claimed optical bench testing
could only be understood by optical engineers.
Picture-taking, they said, was how photographers
should test lenses.
In
the early 1950s, many photographers (myself
included) photographed double-page want ads
from the newspaper and compared the sharpness
of the birdseed-type therein. Later, we realized
that all we were learning was how well lenses
photographed newspaper pages at close distances.
Then
we all gravitated to the U.S. National Bureau
of Standards lines per millimeter targets, which
we could photograph at a near infinity distance.
We searched our test negatives for the finest
pairs of resolved lines we could see through
a 20X or better magnifier. The targets were
printed in high and low contrast so testers
could evaluate differences between high and
low contrast subject resolution.
These
targets were later often supplanted by U.S.
Air Force high resolution targets.
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