Pin Hole Question...
I have been interested in trying pin hole photography.
I have a cambo 4x5, an extra lens board, some sheet brass, and some micro drills.. down to #80 (.0135 in.)
1) What size does the hole need to be, and how do you calcualte the exposure?
2) How "clean" does the hole have to be... can it be drilled or does it have to be done with an etching process?
3) Does the brass have to be really thin like foil... or can it be something thicker.. say .005 in. ?
The hole should be as clean as possible, but I'm pretty sure thickness doesn't matter. The reason many people use thin sheets, I'm assuming, is because it's relatively easy to make the hole clean. Regarding the size:
The size can vary depending on the focal length you what. f/stop of the pinhole is calculated by the size of the opening in relationship to the focal length.
Cleaner the better, or you'll get funky aberrations from light reflecting off the edge of the hole. (Which could be interesting.)
No, thicker than thin foil.
The easier solution is to buy a laser drilled pinhole.
Yes! What Pinholemaster said. Thickness of the drilled material is a variable so thinner and cleaner are best.
Originally Posted by Pinholemaster
I would start by making an f/256 pinhole, in other words, whatever your plate to film distance is, divide it by 256 to get the hole diameter.
Originally Posted by Christoper
If the subject interests you more from a technical perspective, you can investigate 'optimum' pinhole diameters. But be careful, many 'false' formulas are around. There is an optimum pinhole diameter for resolution and another for sharpness, hence the confusion. The eye seems to prefer sharpness over resolution, and that's why the following equation is usually recommended.
d = sqrt (2.44 * wavelength * focal length)
It is based on the George Airy's diffraction-limited disc. Keep all units constant, and if working in metric units, enter 0.000555 mm for the wavelength of green light.
You want to use a thin foil to get the largest angle of view possible and the least interference. Laser-cut pinholes give the best quality, but the beauty of pinholes is their soft images.
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I made a pinhole lensboard that allows me to use any of the three different pinholes with my 4x5 camera. Each pinhole is mounted on a small bit of 2-ply mat board that fits the lensboard. I then simply adjust the bellows draw to the length that I've marked on the small board that holds the pinholes and I'm ready to roll. This gives me some flexibility in the field, which is kind of nice.
To make the pinholes I've used a root beer can (cleaned up of course) and some micro drill bits that I got on the cheap online somewhere. I didn't worry about how clean the holes were myself, but if you drilled ten pinholes and used each one you would like find that each was slightly different, so if you don't like the results just drill a new one I've got some pics of the device on an older webpage but have not gotten around to getting any images from these pinholes posted (sorry). They do a nice job though, as pinholes go...
There are links to bunches of resources on the Worldwide Pinhole Photography Day resource page. The ideal pinhole would have a knife edge to minimize light fall-off at wide angles of view; as such, thin material gives a head start. I used .002 inch brass shim stock for my last pinholes. Down toward .001 the material is so flimsy it's hard to handle. My first ones I used soda can sidewalls, that measured about .004 inch thick. The time-honored pinhole fabrication uses a sewing needle to push a dimple into the foil (not necessarily piercing it) then using fine sandpaper -- #600 or even finer -- to sand off the dimple. You can continue to raise the surface a little and sand until you wind up with the desired hole diameter. With great care this technique can make a pretty good hole; it's likely the laser cut jobs are more consistent and probably somewhat better.
I would be leary of drilling unless you have really sharp bits and a very high speed drill setup. The probability of torn edges and burrs could be rather high.