How to make clean hole
I built a 4x5 pinhole camera that requires 0.56mm hole.
An empty coke can, 0.5mm dia needle and 800-1200 grade sandpapers were used to make the 'lens'.
However when I look closely with a high powered mag glass, the hole edges look rough like saw.
How can I make clean edged hole? Do you have any un-told tricks?
Once you are done sanding, you can go back with the same needle and twist it gently, taking care not to enlarge the hole any more.
I found that .002" brass shimstock works cleaner than aluminum. Don't try to make the hole the finished size in one step. Instead, insert the needle a short distance through the material, sand down the bur, and repeat this until the desired size is reached. If any burr remains, a needle with the tip ground to about a 45 degree cone can be rotated in the pinhole to abrade away the burr. Pinholes the size of yours can be drilled with a no. 74 or 75 drill, perhaps obtainable at a hobby or model shop. A small pin vise is handy for holding the drill, needles, and other pinhole making tools. When using a drill, clamp the material between sheets of fairly hard material to reduce burrs. There is much information on making pinhole cameras and doing pinhole photography at http://www.f295.org/Pinholeforum/forum/Blah.pl.
I've heard that "drilling" with the needle is better than poking straight through, kind of what 2F/2F mentioned. You didn't say which method you used though. I'd also advise trying your pinhole out on a camera if possible before you spend hours fretting about the perfection of the hole - it could be fine how it is despite the edges.
2F/2F, generally that's how I make the hole - slowly drill (with needle) sand drill a bit more sand ... until I get the right hole size.
It looks okay but under a mag glass the edges don't look clean. May be I am unnecessarilly meticulous.
Good idea using brass shimstock, Jim. Also aperture blade of an old lens could be good too. Aluminum is easy to work with but too soft. Thanks for good advices.
aaronmichael, thanks for the advice. My camera has a focal length of 155mm and according to Rayleigh's formula the optimum hole size is 0.56mm. Fortunately it has removable 'lens board' so I can test a few different size holes (lenses).
I've found that a jagged edge hole works good until a light source is in the field of view, then you get flair from the edge of the pinhole. You would get a bit of flair normally, but abnormally so depending on how ragged the hole.
eSPHOTOS -- Some photographers consider Rayleigh's formula to yield too large a pinhole. Rayleigh based his formula on the scientific principles of 120 years ago rather than on the photographic experiences of today. I use Pinhole Designer with a user constant of 1.5 instead of the 1.9 Lord Rayleigh constant. This seems to give the best sharpness in the center of the image, although sharpness in pinhole photography is more subjective than objective. Some of us expend more energy in squabbling over optimum pinhole diameter than in taking photographs. It does provoke us into learning more about this suprisingly complex subject.
First off....that title is great.
Second, I'd try the lens first before working towards "perfection". I found that my really nice, laser cut pinhole lens just produces boring images because they are consistent, sharp, and vignette little (that's due to focal length though). My favorite pinhole looks like a triangle under high magnification but produces great, interesting images. (Mine is made out of a beer can too)
Shoot, and if it's not what you want, experiment some more!
I've been pondering something all morning. I was wondering if a red hot needle for drilling the pinhole would result in a cleaner hole. I quess I'll have to head for the workshop to try it out.
I've made quite a few myself with good success rates - I personally like to use the credit-card sized diamond plates and wet sand them and I work from both sides once the inital hole is made. If you have a larger needle on hand, once the hole to size insert the point as far as it will go and gently turn it without enough effort to expand the hole further. It will burnish any jagged edges that might exist and help true up the circularity as well. Do it from both sides as a final measure and you are good to go.
PS these are the plates I talk about (amazon should have them but they are not hard to find in any case) -the 600 grit works just fine but you may want to use the 1200 to finish but it takes forever to do it all with that one: