Of course, pinhole photography images are always going to be softer than refractive lens images, and while "embrace the softness" might therefore be a good working philosophy there's nothing wrong with attempting to eek out as much resolution as possible from your pinhole system.
Pinhole size and quality is only one factor affecting overall resolution, another major factor being format size. For equal angles of view, a larger film format will require a longer focal length and thus (by Rayleigh's formula) a commensurately larger focal ratio, which will produce images less affected by diffraction. There is also the advantage afforded by larger film formats of needing less enlargement, further reducing image degradation.
But if you're going to find the optimal pinhole, and don't want to purchase commercial electron microscope apertures (which are the best one can find) then do yourself a favor and choose a material a bit better suited than soda can metal. You want to make your pinhole as close as possible to a two-dimensional hole, not a three-dimensional tunnel. The more tunnel-like your pinhole, the more off-axis vignetting and loss of resolution, especially if you are after wider angles of view.
I might also mention that a sturdy tripod is also very important to sharp images, more so than with glass-lensed LF cameras, since your typical pinhole exposure time will be much longer. Another important thing with these long tripod-mounted exposures is not moving your feet anywhere near the tripod during the exposure, especially on soft ground where such movement can slowly but perceptibly move the camera.
Wind-induced camera movement is also an important image degradation factor, a good reason to have both a heavy tripod and heavy (like plywood) camera that can't easily shake in the wind. In this regard, adapting a bellows fitted LF camera for pinhole is probably the worst idea as far as image sharpness in real-world wind conditions. Making a solidly overbuilt MDF or plywood box camera is better, plus you will come to learn to appreciate the camera as a hand-built crafted thing.
Another equally important factor is the shape and roundness of the hole. Uniformity and smoothness can only come through lots of practice making pinholes, which you should do before settling on a final version.
Of course, they all will form an image, it's really a matter of how good of an image will you achieve.
I therefore recommend thin brass sheet metal, no thicker than 2 mil, and use the dimple-and-sand method, using fine emory or a wet stone to sand the tip of the dimple down to ultra-thinness, then barely pierce with the tip of a needle, then continue to sand and ream out the hole until you have the correct diameter and a smooth, clean aperture. With this method I inspect periodically using a loupe, and measure the diameter with the pinhole placed adjacent to the edge of a machinist's scale, marked in millimeters, with the aperture half exposed at its widest point and sufficiently backlit for proper viewing; you can easily estimate the pinhole diameter to within a quarter of a millimeter using this method. You need to practice this method on a dozen or so pinholes until you arrive at the cleanest, roundest, thinnest hole of the correct size for your camera's focal length.
Regarding film, though panchromatic sheet film yields shorter exposure times, don't discount the use of paper negatives, especially graded paper whose image contrast is less affected by the color of the light than with multi grade paper. There's also a theoretically sharper image possible with paper, due to it being sensitive to light of a wavelength shorter and narrower in spectrum than panchromatic film; though in practice you will lose this added sharpness if contact printing your paper negatives.
Like with everything else, there's a science to deriving the best possible results. But it's also possible to over analyze the details. My best advice is to shoot a lot of film or paper as you go along, because experience can teach you much, plus you won't be burdened as much by the prima donnas who eschew the primitive pinhole camera as something they did in school as a kid, but now they're beyond that. You will find through experience that there are only a few things that can truly improve the sharpness of your images (or, more exactly, prevent further degradation), and that also having a powerful artistic vision to you work is at least as important to the audience as is sharpness, which is often over-rated. In this regard, studying the work of other pinhole photographers can give you much inspiration creatively.
Last edited by Joe VanCleave; 07-09-2012 at 08:23 AM. Click to view previous post history.