John's Dirt Cheap Shutter Tapering Tester:
Rewind and remove film if necessary. Put on a lens between 35mm and
85mm. Place the camera in manual mode and set the shutter speed to between
1/125th and 1/1000th. Open the back of your camera and aim at your
computer monitor with the computer and monitor on. A nice light colored
screen, such as a uniformly colored Windoze desktop works best. For an OM
body with horizontal shutter, hold it horizontal. Then fire the shutter
while looking through the open back. You should see a diagonal strip of
light the same width along its entire length. It can take firing the
shutter several times and experimenting with the shutter speed . . .
1/125th to 1/2000th. Slower speeds will make the diagonal strip wider and
faster speeds will make it narrower. For a given shutter speed it should
be the same width along its entire length if both curtains are traveling at
the same speed.
If it changes width:
Narrower toward the bottom right: shutter is tapering
(opening curtain is slower than closing curtain)
Wider toward the bottom right, shutter is doing the opposite
(opening curtain is faster than closing curtain)
This won't tell you how much different it is, just whether you have a
noticeable problem, but it's *much* cheaper than buying a shutter tester.
Why it works:
Your computer monitor (and a TV screen too) is a raster display that has a
beam of electrons scanning from right to left and top to bottom. On a TV
you get a complete top-to-bottom scan 60 times per second in North America
and 50 times per second in nations that have 50Hz power mains (Europe,
etc.). Since a TV is interlaced, it takes two top to bottom scans to give
you a complete image. Non-interlaced computer monitors can be anywhere
from 60 to 72 or more complete scans per second. This is why you need to
keep the shutter speed 1/125th or faster.
-- John
At 18:21 4/6/01, Kelton Rhoads wrote:
Gary wrote:
>Also, you'll want to know the
>speed of the first curtain versus the second, since when they are not
>identical you get tapering. That will result in longer exposure on one
>side of the frame and shorter on the other (in relation to the middle).
>A single sensor shutter tester only tells you the center. Tapering
>generally gets worse with higher shutter speeds.
Hmm. Is it possible to move the single sensor left and right within the
shutter opening to read both sides of the shutter with a single sensor?
Or do these sensors not allow left/right movement? (Considering the
purchase of a tester as found at http://www.homestead.com/cameratester/
or a similar one found at www.micro-tools.com). What sort of shutter
tester do you use?
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