P3D Re: Graflex Stereo

[Tom Hubin <thubin@xxxxxxxxx>]

> Films faster
> than 50 ASA might be a bit of a problem in bright sunlight with the 1/50 sec
> fixed shutter speed.

With most cameras and film the problem is not enough light. Too much
light is easily remedied. If you need 1/9 as much light then make an
aperture for the lens with 1/3 the diameter of the present lens
aperture. That will limit your light intake amd increase your depth of
field. That may also sharpen some of the fuzzy images mentioned if the
cause is a poorly corrected lens. 

You can also use a neutral density filter. You might be able to get that
from a photo shop. If you do not have a place to mount a common threaded
filter you can try to cut and mount your own filter from plastic
sunglasses. Dark sunglasses are about 15% transmissive. 

You can also make an adjustable filter from 2 pieces of linear polarizer
sheet cut round or a pair of threaded linear polarizer filters from a
photo shop. Stack them as a pair, rotate one with respect to the other
to make as dark as you wish. However, this will give you the effect of
using a polarizer to take the photo. If you rotate the pair together
while looking at a polarized light source such as the north sky, then
you will see the effects of a polarizer.

If you do not want the photo to look like it was taken with a polarizer
then use circular polarizer for the first filter and linear polarizer
for the second. The circular polarizer normally uses a a linear
polarizer first then a quarter wave retarder to convert the linearly
polarized incoming light to circularly polarized outgoing light. Use the
circular polarizing filter in reverse. You want the quarter wave
retarder layer first and the linear polarizer layer second. If you use a
threaded filter you should be able to remove the plate, flip it over,
and remount it in the threaded holder.

To test this, hold the pair of mixed polarizers up to a polarized light
source like the north sky. When you rotate either of the polarizers you
will vary the light transmission from about 25% to nothing. If this does
not work you probably have the circular polarizer with the linear
polarizer layer first and the quarter wave retarder layer second. Flip
the circular polarizer over and try again. Once that works try rotating
the pair togeteher. There should be no obvious change.

You can get circular polarizers from photo shops and in sheet form from
Edmunds Scientific. You can also use a video monitor anti-glare filter
for this. It is really just a circular polarizer. It may be right or
left handed circular but it does not matter which for this application.

I do not have a cheap improvement for shutter speed. So you are stuck
with stills or slow moving subjects. I use a single SLR camera and it
don't get any stiller than that. Flash would help close in and fast. A
liquid crystal shutter might help speed but it is likely to be
polarization sensitive. There are ways to alter the polarization
dependancy but you are probably better off graduating to a more
versatile camera when shutter speed becomes an issue.

Sorry about the rambling. I started to suggest how to reduce light with
an aperture and just could not stop talking.

Tom Hubin
AO Systems Design
thubin@xxxxxxxxx


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