I have done a fair bit of pinhole photography, and I find the way that works
for me to make lenses is as follows:
Get the foil from the bottom of a pre cooked pie tin and cut it to about
11/2" sq. Make a dent in the centre ( do NOT pierce it) with a medium sized
needle. Get hold of a flat sharpening stone, the type that is used for
sharpening woodworking chisels etc. and gently, with very light pressure rub
the indent along the mildly abrasive surface, keeping your finger pressure
steady over the indent. As soon as the top of the indent has worn away (
this may take several attempts as it is vital that you stop as soon as you
are 'through'), stop.
Now the interesting bit!
place your partly finished lens onto the negative carrier of your enlarger
and take the head to its maximum height. switch on the lamp and focus on the
baseboard. you are trying to obtain a perfectly circular hole, it will not
be yet!. You will probably find that the hole is very jagged and elliptical
in shape. Now, get a fine sewing needle ( I push the 'eye' end into a cork
as I find it easier to use and handle this way) and ever so gently place the
sharp end just in the hole you have made and spin the needle between your
fingers. I do this with the foil still in the neg carrier, but removed from
the enlarger of course.
You may need to do this several times before you get the perfectly circular
hole, but you WILL do it, just keep trying.
The biggest problem is making the hole small enough. I have not tried
pinhole 35mm, as pinhole negatives are not good for enlargement, but it is a
quite simple matter to make a 5x4 camera out of MDF and use a standard
darkslide as a back. These give acceptable size contact prints and you can
get away with a slightly larger aperture. 8x10 is obviously even better, but
film costs start to get a little prohibitive.
After you have made your lens, you need to measure the aperture in order to
work out the f stop. I find the best way to do this is to put a clear
plastic ruler in the negative carrier, place some plain white paper on the
baseboard, focus on this and mark the paper with the enlarged graduations,
then replace the ruler with the lens and you will be able to easily measure
the diameter of the hole.
If you need any more info, please let me know.
Steve
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