T3D Re: apertures

[john bercovitz <bercov@xxxxxxxxxxx>]

> Yes, I want to just put in some metal that has f22 hole in it.  
> [...]
> Anyone know how I would make the apertures, or buy them?  I don't have
> equipment at home to do this, and I wouldn't know what size bit to
> use anyway.

They're easy to make.  Go to an auto parts store and ask for some brass
(easy to drill) shim stock.  Get a couple of pieces of flat scrap metal
and make a sandwich with the brass in the middle.  Then drill through
the sandwich with the correct size drill bit.  The sandwich approach
gives you a burr-free hole.

The size of bit is easy to calculate but I guess I said too much last
post so it wasn't obvious.  Divide the focal length by the f/number.
So if the focal length of the lenses is 30 mm, then 30/22 = 1.36 mm
hole.  It doesn't have to be exact by any means.  A 1.4 mm drill bit
is fine.  If you use US measurements, that would be an 054 drill.  So
you can pick a #55 dril which is 052 or a #54 drill which is 055.
Number drills are also available at the auto supply store.

What _is_ the focal length of a Nimslo lens?  I'm just guessing it's 30.

You could also buy the apertures from Edmund depending on how well
your job pays.  8-)  OK, I just looked in Edmund and their largest 
pinhole appears to be 1000 microns.  Not much help.  Their cheap ones
are $26 each.  Melles Griot only goes to 200 microns.  You might search
on aperture/pinhole/spatial filter and see what you come up with.

John B


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