Date: Sat, 10 Jul 1999 08:33:39 -0700
From: Norma Foltz <flzhgn@xxxxxxxxxxxxx>
Subject: [OM] I like the Zuiko 4.0/200mm
<snip>
_____________
Now a question for the OM group:
Does anyone have recommendations for making a pinhole that can be used on
an OM camera or any examples of pinhole photos done with an Olympus Camera?
I am thinking of making a pinhole attachment that I can use with my Olympus
extension
tubes, etc.
Hank Hogan <flzhgn@xxxxxxxxxxxxx>
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Norma,
Title says it all. I found this in a site on amateur telescope making, and
thought I would pass it on. I haven't actually tried this, but the method seems
to make a lot of "horse sense" to me.
regards,
Mahlon
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How to Make Precision Pinholes
Conducted by Roger W. Sinnot
Cribbed without permission from Gleanings for ATM's, Sky and Telescope May, 1981
<background info snipped>
Let us turn to the New Photo-Miniature, where the directions are given:
Before we can make the needed pinhole, we must have the needles of the
right size. SInce the beginnings of
pinhole photography, three sizes have been most generally used, No. 10,
about 1/55 of an inch in diameter, No.
11, about 1/65 of an inch, and No. 12, about 1/75 of an inch in diameter...
FOr use, the needles should be
forced, eye first, into little sticks or holders about the size of a lead
pencil, or a fine pin-drill may be used as a
handle...
Metal pinholes may be made of copper, brass, aluminum or even silver. They
may be made in two ways, using
rather heavy, 24 gauge or so, metal or using very thin metal and mounting
the finsihed pinhole on thin card or
fibre...
If the heavier metal is used, we must first cut a cup-shaped depression in
it by starting to drill with a 1/4 inch or
5/16 inch twist drill, stopping just before the drill begins to go through.
We must be very careful not to puncture
or tear the metal with the drill, but we do want to get the bottom of the
depression as thin as possible. After the
depression is made, the procedure is just the same whether we use the thin
metal or the thick.
The metal is laid on a yielding surface, like several thicknesses of
blotting paper or a piece of linoleum. With a
blunt rounded point like that of a used lead pencil and gentle pressure, a
dent is made in the bottom of the
depression or in the center of the pice of thin metal. The metal is turned
over and the bump raised by the pencil
point is gently rubbed away, even with the surface, with a fine sharpening
stone or a smooth file. This results in
a very thin spot in the center of the metal. The metal is now turned
face-up again and laid on a block of wood
or a piece of cardboard. The thinnest center of the metal is now just
punctured with the point of the selected
size needle. This raises a burr on the back, which is rubbed away with the
stone or file. The needle is pushed,
not twirled or twisted, through a little farther and the burr is rubbed
down. This is all repeated until the needle
passes through smoothly to its largest diameter. The needle-hole should now
be polished gently with the
sharpened point of a toothpick, very gentle because the edge is very thin
if properly made. The needlehole
should be blackened with India ink or dull black lacquer, but preferably by
heat and fumes from sulpur or a
burning match. The edge of the aperature must be blackened, above all else,
to avoid stray reflections.
Examine the needle-hole with a magnifier and run the needle, used in
making, through the aperature carefully
to clean out any matter resulting from the blackening process.
For the rubbing down of the burr, various implements may be used; the
principle thing is to rub lightly. Fine
grained India, Washita, or Carborundum sharpening stones or hones may be
used. An old style slate pencil,
which is all slate and not cased in wood, is excellent if used deftly. It
should be first rubbed down on sand
paper or emery paper until it has a blunt bevel on the end instead of a
point. Very fine emery cloth is one of the
best things to rub down the burr; it should be wrapped around a little
block of wood about the size of a
domino...
These sure, careful steps stand in sharp contrast to the hit-or-miss procedures
mirror makers have generally used to make
Foucault pinholes in aluminum foil. Yet when I tried out the method on a sheet
of brass 0.025-inch thick, it proved easy and
fun to do, and gave exquisitely thin and circular pinholes. I now have a whole
set of various sizes, for photographic and
mirror making purposes.
Among the old-timers, Rev. W. F. A. Ellison in particular waned against too
small a hole in Amateur Telescope Making ---
Book One (page 84) because diffraction effects might lead to misinterpretation
of the mirror's figure. He and Russell W.
Porter merely suggested a fine needle for piercing thin metal. G. W. Ritchey,
who made the 60- and 100-inch materpieces
for Mount Wilson Observatory just after the turn of the century, preferred to
test with a 1/250- to 1/500-inch pinhole, much
smaller than an ordinary needle can produce. Honing a needle to make it smaller
is described in ATM-2, halfway down on
page 89; then the photographer's directions quoted could still be applied.
The size of a pinhole for optimum photographic imaging was investigated by Lord
Rayleigh long ago. First he pointed out a
plane parallel glass window will meet his 1/4-wave tolerance as a substitute for
a lens, provided the focal length exceeds
about 20,000 times the square of the aperature in inches. This being so, he
noted, one can take away the window and use an
opening of the same size instead!
According to his formula, a 1/50-inch pinhole should be used at 8 inches or
more, although in photography there is nothing
really critical about this. A 1/4 inch "pinhole", which might be used to project
sunspots on a screen in a dark chamber should
have a throw of 1200 inches or 100 feet; the 11-inch solar image will show
diffraction-limited detail likle that seen with a
properly filtered 1/4 inch telescope (resolution 20 arc seconds. A heliostat and
a long tunnel would be ideal for such an
experiment.
A cardboard tube with a pinhole objective atone end an an eyepiece at the other
becomes a pinhole telescope. I have tried
such an instrument on landscapes by day and on the Moon, planets, and double
stars by night, hoping to find out whether
more can be seen this way than with the naked eye alone. I'd like to hear from
readers who try the same thing.
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