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paulbeard
08-29-2006, 04:57 PM
from my experience, it seem like the 2 nanometer (nm) pinhole is easiest to make. I just made a new pinhole lenscap assembly for a Holga and since I now have a flatbed scanner, I decided to take a look.

This a rough look at what I have. I scanned it at 4800 dpi, brought it into photoshop, and then did my best to measure it. I think I got a lot of reflection/refraction in the scan: the hole looks beautifully round to the eye, and I can look through it and see a good round image.

As you can see it seems to be right on the .2 mm mark.

The technique was the tried and true sewing needle in an eraser method. I bought a set of sewing needles at my local craft emporium so I could get some different sizes (mostly so I could get small ones). Took the smallest and backed it, eye-first, into a block eraser, and to make a pinhole I just prick a sheet of brass. I find it impossible not to go right through, but it doesn't seem to do any harm. A quick touch on the other side with some 400 grit sandpaper, and that seems to be it.

I suppose I could try the other needles but I don't have a need right now to go bigger on the holes. 2 nm seems fine.

I notice American Science and Surplus have a set of hobby drills (http://www.sciplus.com/singleItem.cfm?terms=11846&cartLogFrom=Search) and teeninesy drill bits (http://www.sciplus.com/singleItem.cfm?terms=1385&cartLogFrom=Search) that might make this kind of work easier. The smallest would get you to .33 mm with a bit more precision than a sewing needle ;-) Attached files http://f295.f295.org/uploads/pinhole_987.jpg (http://f295.f295.org/uploads/pinhole_987.jpg)

Jim Jones
08-29-2006, 09:50 PM
When scanning pinholes, the exposure can alter the apparent size of the hole. This is especially true when using a transparency adaptor if the scanner tries to automatically adjust the exposure.

Making small pinholes with a tiny drill requires much care. The drill often leaves a burr. Backing the pinhole material with a fairly hard surface like Masonite can reduce this. The material should be held snug against the Masonite. Small twist drills are fragile. For drilling deep holes, the twist feature helps remove chips. This isn't necessary in a shallow hole like a pinhole. For working in thin stock, what is called an engineer's bit or V-drill might work better, and can be fabricated at home by someone with better eyes and steadier hands than me. Needles or small wire stock could be ground to make them.

Years ago an institution with a need for thousands of easily made pinholes of about 3 or 4 microns made a punch that worked somewhat like a paper punch.

Paul's method, or any of the variations of it, is probably the most practical for most of us. For very small pinholes. I clip the head off of an ordinary pin and chuck it into a pin vise with little of the point protruding. I dimple brass shim stock with the pin, and with the pin still in the dimple. grind pin tip and dimple on a fine whetstone. Leaving the pin in place during the grinding reduces any burr. If the pin must be removed for checking the hole size, any burr on it should be removed before resuming grinding. An optical comparator micrometer is ideal for quickly checking pinhole diameters, but they seem to be scarce on the market today.