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A SIMPLE SLIDE BAR
The "slidebar" provides the
simplest approach to macro as well as to normal stereo
photography. It provides a means to line up the camera
while permitting horizontal movement in order to obtain a left
and a right frame. Assuming you have either a 35mm SLR
or a digital camera, you
need only to construct a simple slidebar to try out stereo
imaging of small objects. While professional slidebars
can be purchased for ~$50 - $100 (see
http://www.stereoscopy.com/jasper/slide-bars.html),
you can make one for a dollar or two.
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Fig. 1.1
SIMPLE SLIDE-BAR
Here are the parts you need.
A two foot 2x2 board (find a straight piece)
A 1/4 - 20 screw about 2" long.
A 1/4 - 20 screw with about 1/4 " of threads
(may be cut or ground down).
A piece of 1 1/2 " angle aluminum, cut to
about 2" - 3" long.
A flat piece of plastic or wood about 1/8 to 1/4
inch thick, same length as angle, 1 3/8 wide (to fit
on inside of the angle). |
Drill a 1/4" hole in the angle
aluminum as illustrated. This will allow you attach the
bracket to the bottom of your camera via its tripod socket.
Drill a 1/2" hole in the plastic or
wood spacer, with the hole centered over the 1/4"
mounting hole. This spacer is necessary so that the
tripod-hole screw head (on the short 1/4-20) will not
protrude. It is "counter-sunk" into the
spacer.
Attach the plastic/wood spacer to the
inside of the angle using silicone rubber or epoxy. It
helps to lightly sand or steel-wool the joining faces just
enough to generate tiny scratches for the glue to adhere
to. Align the spacer so that the 1/2" hole is
centered over the 1/4" hole in the aluminum, as shown in
the illustration.
Drill a 1/4" hole at the midpoint of
the 2x2. Use the 1/2" drill to countersink it too.
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Fig. 1.2
SLIDE-BAR OPERATION
Attach the 2x2 to a sturdy tripod
with the long screw. Some tripods are 1/4-20
threaded. If not, use a nut.
Mount the bracket to the camera
base as illustrated.
Now you can simply slide the
camera sideways between R and L shots, and it will
stay nicely aligned, with parallel pointing.
You can add a clamp if need be. |
Choose a static subject. Set up the camera and take
the first frame. Slide the camera left (or right) a
small distance and shoot the second frame. The
separation should be approximately 1/30'th the distance to the
subject. Some tips for this kind of 3D photography are to a) photograph objects that don't move while you are
sliding the camera for the second shot, b) maintain constant lighting
angle and intensity for both shots, c) use a high enough
aperture (e.g. f22) to get good focus across the
subject, d) try to eliminate highlights or details
in the out of focus and "far-away" background.
The two (L & R) images you obtain can be viewed as
pairs of prints, or in a hand-held slide viewer.
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