Re: super 8 shutter speed, formula

From: Jim Carlile (email suppressed)
Date: Thu Mar 08 2007 - 21:54:08 PST

Here's the rough and ready formula for determining the shutter speed:
(Shutter Angle/360 degrees) X (1/frames per second)
or, the shutter angle divided by the total degrees of the shutter coverage,
times one divided by the frame speed, its reciprocal.
Say your shutter on the Canon is set at 220 degrees (not all models can do
this), and your motor speed is 64 frames per second. Divide 220 by the total
360 degrees, then times this by one over 64. The result will be about 1/104th
of a second.
It's easy-- you're just multiplying two simple fractions. Plug in whatever
values you want.
But your bigger problem when using an external meter to determine the
exposure is that the f/stop value of a zoom lens will not correspond to that of the
meter reading. In other words, the glass elements of a zoom lens will soak
up light, so that the f/5.6 of your camera's meter reading will not be an
accurate setting. There are two solutions to this:
1) figure out through experimentation how much your lens is generally off
compared to the meter (it's probably about a stop), and then manually
compensate for this all the time, always adjusting for the film speed difference, or
2) Rely upon the camera's internal meter alone, and then manually tweak it
to a smaller aperture, if the film you are using is beyond the camera's ASA
range. I believe most super-8 cameras automatically set the ASA rating at 160 if
 they cannot find a known cartridge setting.
The second is probably the easiest way to use higher ASA films. An ASA 500
film is --what-- about 2 stops faster than 160? If so, then after you get your
internal reading, boost it up two f/stops to a higher number.
Obviously, a couple of trial and error cartridges will be needed to see what
works best. If you bracket your exposure settings and keep records of it
all, it's really easy.
Jim Carlile
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