Hi,
> Date: Sat, 31 May 2003 16:46:05 -0700
> From: Moose <olymoose@xxxxxxxxxxxxx>
> Subject: Re: [OM] Body Cap with a hole, is pinhole "lens"?
>
> I suspect the fuzziness was a result of a poorly formed and likely too
> large hole. If you check the web resources on this subject, you will see
> how important a very smooth and thin edged hole of proper size is. And
> how relatively difficult such a hole may be to produce.
I made my own too, in photography classes, about 5 years ago. It's a Genuine
Olympus Body Cap (TM) with a 5mm hole drilled into it in the middle. On the
inside, I stuck an aluminium sheet with a .1mm hole in it. I was lucky because
somebody in my class back then knew a precision instrument builder and he got
us a sheet with a pile of those holes. Holding it before my eye, it looks as
round as it gets.
Blocking the camera in B and measuring the distance from the pinhole to the
camera pressure plate, it's about a 50mm, so I rounded it off to f512. That
makes calculations easy: the exposure is 1000 times more than on f16. You need
a *very* bright scene (and very sensitive film) for handheld exposures :-) But
it's practical, because I can compose & meter the light with any 50mm lens, put
on the pinhole and come up with a decent exposure. Very easy.
Doing a very quick google search, I came up with a link for the optimum
diameter of the hole
http://members.rogers.com/penate/pinsize.htm
The reason why there's an "optimum" diameter is that diffraction kicks in again
when the hole is too small. Light will scatter on a wider surface instead of
being focussed. That's the case with mine: for a 50mm lens, the hole should be
about .25mm. I notice that on A5 (15x20cm) prints, the lack of resolution is
already such that it looks like a pre-1900 picture. It's not the best, but
it's quite charming anyway.
I have been considering getting a fine and sharp needle, and trying to enlarge
the hole, but as has been mentioned in the thread before, I'm worried that it
would ruin the regularity of the current hole. And as the web page mentioned
above puts it: it's not because there's an optimum for diameter size as far as
sharpness of your pictures is concerned, that you like that kind of pictures !
Peter.
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