Effect of Thickness of Pinhole Material?

[AndyDDuncan]

I'm currently building a few different pinhole cameras, one that will accommodate 4x5 or 5x7 film/paper, one that will just do 4x5 with 4x5 film holders, and a scaled up version of the second camera for 8x10. I've made and used several pinhole cameras in the past, and I only ever used soda cans for the pinhole, which is about 0.004" thick. As I've been doing more research about different cameras, I've read of some people using 0.001" brass shim stock for their pinholes. So my question is this: does the thickness of the material used for the pinhole have an effect on the image made with it? I've seen several discussions about the diameter of the pinhole, and how roundness can affect the image, but nothing really about the thickness of the material.

 

[AgX]

The thicker the sheet the more vignetting you will get.

 

[DWThomas]

After a point, thickness comes into play because the pinhole becomes more of a tunnel. The longer the tunnel, the more fall-off at the extremes, and if really thick, you will get full vignetting. I had used 0.002" brass stock for a few that worked well, and then succeeded in making a couple out of 0.001". This past April, I discovered one of those later ones had a crack in the foil! I theorize the sanding, plus using some sort of nasty chemical to blacken the finished plate, may have weakened it a bit too much.

My first pinhole plate (at least in the 21st century) was made with soda can stock. I would say my later results have been better, but I also blackened that first one by smearing a felt permanent marker around it, and it could be that left a small blob or two in an unfortunate location. A careful dimple-and-sand job actually creates a knife edge for the hole, so I would expect the sensitivity to material thickness to be less important as long as you don't start using 0.032" or some such thing.

My 1.3 (after tax) cents,

 

[markbarendt]

If you drill a hole it generally creates two sharp edges; in that case thickness does matter, the thinner the better.

If instead you dimple the metal and then sand the dimple off a single sharp edge is created, which is better yet.

 

[AndyDDuncan]

Great info so far! Thanks! I'm going to try this dimple and sand method on these. Do I use a needle to make the dimple, or something a little more blunt?

 

[markbarendt]

It doesn't need to be a needle, just sharp and round. You control the size by how much you sand.

 

[AndyDDuncan]

I take it it's still possible to end up with an asymmetrical hole? Not that I'm so worried about a perfectly round hole enough to buy a laser cut or chemically etched pinhole.

 

[markbarendt]

Sure, thats true of most any mechanical method.

You are right, IMO, not to worry. If you were truly worried about perfect sharpness a pinhole wouldn't be in consideration.

 

[DWThomas]

I take it it's still possible to end up with an asymmetrical hole? Not that I'm so worried about a perfectly round hole enough to buy a laser cut or chemically etched pinhole.

It is possible, but part of the process is to work slowly and gently. I use wet-or-dry sandpaper wet, in circular motion -- usually at least 400 grit or finer. I usually use a piece of mat board as a backup surface to work on. Once a dimple has been raised and sanded enough to open a hole, one can gently rotate a decent sewing-type needle in the hole to enlarge it slightly. That leaves an "upset" edge which can then be sanded down gently and carefully. Keep working the needle from the same side and sanding on the opposite. This process can be repeated to "sneak up" on the final hole size. What I consider perfect (not that I necessarily achieve it! ) is at the point where the dimple has been sanded down level with the surface of the plate leaving the desired hole diameter with a knife edge. As I understand it, laser cutting does not give a knife edge, although if the plate itself is super thin, that issue is pretty much academic. Chemical etching does tend to leave an edge, but doing really precision chemical milling is probably beyond a do-it-yourself process. As Mark alludes, for the ultimate sharpness, a lens is in order -- although a pinhole generally gives way more depth of field than a lens.

 

[AndyDDuncan]

Once again, thanks for the advice and shared knowledge. I'm real anxious to finish these cameras up and start making photographs with them!