----- Original Message -----
From: "ROGER ARMOUR" <roger@rharmour.fsnet.co.uk>
> Subject : Ultra closeup photography.
> Bill Erickson in replying to Rachel Mallon's questionnaire mentioned ultra
> closeup pinhole photography. Please tell me what this means. What subject,
> how close, and how is it illuminated? I experimented with photographing a
> coin at diminishing distances obtaining magnifications of 20X and more at
> 1cm with a 0.16 mm pinhole. Lighting became a problem and the image became
> blurred.
I have no experience whatsoever with close up pinholing, but that won't
prevent me from giving you my 2 pennies worth of comments:
Remember that when the distance pinhole lens to object is decreased, not
only the object's image is augmented but that of the shadow of the material
where the pinhole was made, too, the latter is what forms the images, hence
the blurring of the images you are observing. Your circles of confusion get
too big and confusing :-) . To increase the geometrical sharpness you have
to use a smaller pinhole than the "optimum" for the distance pinhole to
film, which if I am not mistaken is, for your case, probably around the
200mm (for 20X at 1cm), by using a .16mm pinhole you are in the right track,
but IMO you need to make it even smaller, according to my analisys, if your
camera has a length of 200mm, you should use a pinhole as small as 0.035mm
for 20X magnification (more explanation on that upon request).
As for lighting the coin: - make your pinhole cameras with a tapered front,
this would allow you to illuminate your coin easily. - increase the working
distance by increasing the length of the camera, if you use a 400mm cameras
you'd have 2cm working distance for 20X. - use a ring flash around the
tapered front of the camera.
Guillermo
Received on Sat Dec 22 13:51:32 2001
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