Andrew Dacey wrote:
> Mainly what I'm looking for is some info on how to go about the
> conversion. First, is a body cap usually light tight around the edges
> (obviously I could check this fairly easily but may as well start with
> the wisdom of the list). Second, what's the focal length and what size
> pinhole would be needed to cover the 35mm frame? I'm assuming that it
> would be the flange distance plus however much the body cap extends
> out from there, is that right? And finally, what's the best method for
> doing the conversion? I thought of drilling it but don't know if I'd
> have a small enough bit and has the drawback of having a fairly thick
> piece of plastic so I'd need a wider opening to avoid vignetting I
> imagine. The other thought would be to cut out a larger hole and then
> attach a copper shim (which I do have). The added bonus I see here is
> that I could use extension tubes and a different shim to get different
> focal lengths.
---------------------------------
I'm sure a Google search will turn up 1000 sets of instructions for
building you own. But I will make a couple of comments.
1) I doubt that a lens cap is light tight. However, a paper thin gasket
of some flexible material glued on the back side would probably rectify
that. Alternatively, a ring of tape around the outside. Perhaps better
yet would be a screw on metal cap. Very sturdy and light tight.
2) Yes, drill a larger hole and then glue on a piece of foil with the
pin hole in the foil. A good performing pinhole must not only be very
small but also very round. If made by hand they are done by using a
sharp pointed needle pressed into the foil against a piece of glass as a
backing. Once the needle is through the foil rotate the needle in your
fingers to round out the hole. Careful, don't make it much bigger.
Chuck Norcutt
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