Hi Rich - A couple of ideas for consideration. Not necessarily the gospel though!
Since you have been investing in pinhole for years, it may be worth switching from spending lot of time to spending a little money. If you buy just one commercially manufactured laser-drilled pinhole, then you will have a known "gold-standard" as a reference. The thin wall, blackened circumference and sharp edges of the commercial piece might save years of misplaced effort. If the commercial hole is sharper for you then you are further along the path. If not, then you still have a righteous pinhole for your next camera. Regardless of outcome, you will truly know how good (or lacking) your own pinholes are... and what's that worth?
Next, is it possible that contrast is an issue? Could light be bouncing from your film to the wall of the camera, and then back to the film? Assuming you are painting the inside of the box, some matte black paint can bounce or scatter light more than you might think. Maybe a switch to a black velvet lining inside the camera would help. Or baffling. Or both!
Also, are you totally sure that your box material is 110% opaque? Far out question, but one never knows.
Along the same lines, are you "smoking" the edge of your pinhole aperture? This can help to eliminate stray light that might degrade an image.
Crazy as it sounds, sometimes problems can be diagnosed by "seeing what the film sees." If possible, try getting an eyeball onto the film plane of the camera. This will of course require totally excluding all other light sources, so you may find yourself staggering around the yard with a camera duct-taped to your head! Leave either your nose or mouth uncovered!! In any case, once your eye adjusts you may see obvious problems such as internal reflections, light leaks, hot spots, etc. (This technique also works wonders with Feds and Dianas!)
Same logic in revese applies to film holders. Go into dark room. Install holder, pull slide, remove pinhole, shine flashlight in through front of camera and look for leaks from the outside.
Finally, have you tried a few varieties of film? Say, a controlled experiment with T-grain fast and slow film along with conventional fast and slow film.
It would be instructive to try a controlled test with supposedly undersized or oversized pinholes as well.
All of this will leave you with no time to actually shoot the damn thing, so I promise you will no longer be vexed with unsharp images!
Originally Posted by Rich Ullsmith
Thickness of the metal could be a bigger problem than it is often given. You can buy a sheet of .001 stainless or brass from http://www.smallparts.com that will last you a very long time. While you are there, you can get those tiny little numbered drills, spin them fast in a dremel tool and they make great round holes in the thin material. When drilling, back up the .001 metal with something much thicker of brass or aluminum, this will help prevent the metal from distorting due to the pressure of drilling.
My local Ace hardware store has a packet of brass shim stock from .001" up. For larger pinholes .002" is easier to work with. The old method of dimpling and sanding the brass thins it down anyhow.
Thanks everybody, for giving me a few things to think about.
I shoot from those old vietnam era 50cal ammo boxes . . .divided in half, each side holds a 4X5 sheet. I made a mess of pinholes in dead-soft stainless steel shimstock, I want to say .01mm. I measured them all, inspected them under a scope, and installed them in the cameras so that two very similar apertures are on each camera, for bracketing. However, I did not smoke the pinholes, the benefits of which I have known for some time, mainly out of laziness.
The cameras are not only light tight, but airtight and water tight as well. The 58mm filter rings are glued on, and the filter over that, then another blacked out filter over that as a lens cap. Light leakage is definitely not a problem.
I'm just saying, I have seen pinhole images, albeit on a computer monitor, that looked to me to be focused light. I know a laser drilled hole would be an improvement, but I've seen mine up close, and there's nothing wrong with them. I know the black will help, though. But buying anything for my boxes, vice scrounging, would rob me of the perverse pleasure I get from this stuff.
I've never smoked an aperture. A few other things, perhaps, decades ago, but I can't recall.
Don't count on a laser-drilled hole being any better. I have some with nasty slag around the aperture. I don't know if they are typical or missed a cleanup process after the laser one. They were gracefully donated to me so I'm not going to badmouth them too much. I do have another size that looks clean.
I tried some loose silicon carbide & water but didn't have the patience to wait for something to change...got a few scratches in the SS after a while.
I may try one of those imitation Dremel bits with the 'diamond' grit under a microscope & see what I can do to get them flat.
Many people have observed better results with homemade ones because some of the homebrew procedures result in thinning of the aperture material.
There are procedures to alter aperture edges called apodization. Comes from the Greek for footless. This refers to the classic undulating Bessel waveform crossing thru zero repeatedly causing the intensity variations with distance. A typical apodized aperture may be altered to remove those variations and produce a single Gaussian curve without all the repeating maxima and minima.
Homebrew holes that result in other-than-perfectly-flat-and-round apertures may be accomplishing some form of asymmetrical apodization.
I want to experiment with non-round holes. I know the math is different and the maxima/minima mentioned above are different, and there can be some ugly artifacts like lenses with weird shaped apertures. I am not sure I believe yet that roundness is important because the square aperture is one of the examples in diffraction theory (slit, square then round in that order I think). I think the different theoretical behavior of non-round holes may throw off comparisons to round when designing with rules for round holes.
If you have the motivation to make your own holes, and are checking them I'd say you may as well keep doing that.
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If your apertures are 0.01 mm, they are far smaller than anyone's calculations for optimal at a distance that covers 4x5.
That could be a reason for excessive blur.
I can think of two good reasons for non-circular pinholes. Elliptical pinholes should (in theory) give slightly better images in some panorama cameras. Square pinholes can be made adjustable, so one pinhole can be used at a wide range of focal lengths. Perfecftly round pinholes and lens apertures are usually preferred, although my Leitz M-mount Super-Angulon f/3.4 21mm has a nearly square aperture at smaller openings, but the images are certainly good enough.
Sorry, Murray, I meant the shimstock I made the holes from are on the order of .01mm, not the aperture itself.
If you tend toward building alot of cameras of the same f.l. or want to share them in a group buy, look up emdiasum, a supplier of electron microscopy materials.
They sell electron microscope 'grid' apertures, called 'single hole', or 'Gilder Grids' by some suppliers. They are electrodeposited copper, very thin, with clean round holes in a range of sizes. A little tiny to handle (3 or 3.15 mm diameter), cost about $20-25 per vial of 100. Users find them to be as good as or better than laser-drilled.
They will darken to a dark gray in selenium toner.
I pick them up with black photo tape when ready to mount them. I gave up on tweezers. Maybe those little vacuum pickup tools would work well if it's a habitual thing.