Thickness limits of pinhole appatures

I'd like to know others thoughts on making appatures out of brass, copper, gold alloy and silver, American coin of 90%, some 40%, sterling and some fine, 9999.

I have plenty of copper and brass on hand, in different thicknesses and a small piece of dental gold, a filling of about 12k.

The silver types listed above are also nice too work with

I also have jewelers tools, etc for working these metals and I want advice on which metal is an ideal ductile material that will allow a smooth, round hole, by whatever method folks have to hand.

I can blacken all but the gold, with Liver of Sulfer but my biggest concern is how round a hole will each make and how thick the metal should be.

I have a good micrometer, so thickness can be measured.

This pinhole is for a full frame 5"x7" pinhole camera and I want it to as sharp as possible this no burrs or oblong openings

As the pinhole gets smaller sharpness increases to a maximum, after which, the image just gets darker, but not any sharper. With a view camera, you can use some trial and error to get the brightest, sharpest hole.

You can place a very thin metal sheet under pressure between thicker sheets and drill it then. This yields a better hole than drilling the thin sheet directly.

AgX said:

You can place a very thin metal sheet under pressure between thicker sheets and drill it then. This yields a better hole than drilling the thin sheet directly.

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That is clever, must remember for next time.

pinhole metal should be rigid, perfectly flat and very thin. Most use brass or stainless steel.

I have a friend who has had good success using the material from beer cans, blackened suitably.
He also has the resources to be able to mount very thin brass (IIRC) shim stock in an appropriate holder, and has had excellent results with that.
He has a neat trick where he mounts the result in an enlarger and projects the (very dim) image of the pinhole on a wall. That way he catches pinholes that are significantly off from being a circle, or exhibit large edge burrs. He discards those.
He also uses another enlarger set to a high magnification with a short lens to calculate the actual pinhole size.

awty said:

That is clever, must remember for next time.

pinhole metal should be rigid, perfectly flat and very thin. Most use brass or stainless steel.

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One could use stainless gauge or shim strips.

Pinhole metal does not need to be rigid, as long as it's supported both when you drill the hole and when mounted in the camera.

I've made many pinholes from .001" (= .025 mm) brass shim stock; this stuff is less stiff than regular printer paper. The pinholes I've made in this material have ranged from 0.2 to 0.7 mm with good results.

Ideally, the thinner the layer with the actual pinhole, the better; if you have a thickness comparable to the diameter of the hole, you lose sharpness due to the doubled diffraction effect (from the front edge of the hole, and from the rear). The true optimum thickness is zero at the edge of the hole; this can be approached by "dimple and sand" method of drilling the hole in a somewhat thicker material like beverage can aluminum; the edge of the hole can be pretty much a knife edge (but it's hard to control the hole size with this method, hence why I haven't used it myself).

Also, smaller isn't better beyond the point where diffraction effects outweigh the simple geometric projection of the hole. There's an optimum for any given projection distance -- the best compromise between geometry and diffraction -- and there's a calculator for it online at Mr. Pinhole web site. This provides a guideline, however, not an exact solution; if you expect to make a lot of close-up shots, for instance, you will gain by making your hole a few percent smaller than the calculated optimum.

Another factor is that the longer the projection distance ("focal length"), the larger the optimum hole, which overall detracts from final sharpness. Couple that with the well-known effects of large vs. small film, and that 5x7 will likely be best with around 100 mm projection (pretty wide, a bit less than half a "normal" focal length) as the best tradeoff between "too wide to compose for" and "optimum hole gives too much fuzz". Even 4x5 with 135-150 mm projection looks good in a contact print, however, and any large film at any reasonable projection distance will tend to look better, just because you normally view from further way or with less magnification the larger the film.

Bottom line is that for large format you can’t make the hole too small, because no matter what, you are going to have long exposure times. Some foil, a pin and two seconds of work are all that is needed.

I use the aluminum from pop cans. Poke through with a pin (don't push all the way through to the shaft), and gently sand with wet/dry sandpaper. Blacken inside with permanent marker.

eli griggs said:

I'd like to know others thoughts on making appatures out of brass, copper, gold alloy and silver, American coin of 90%, some 40%, sterling and some fine, 9999.

I have plenty of copper and brass on hand, in different thicknesses and a small piece of dental gold, a filling of about 12k.

The silver types listed above are also nice too work with

I also have jewelers tools, etc for working these metals and I want advice on which metal is an ideal ductile material that will allow a smooth, round hole, by whatever method folks have to hand.

I can blacken all but the gold, with Liver of Sulfer but my biggest concern is how round a hole will each make and how thick the metal should be.

I have a good micrometer, so thickness can be measured.

This pinhole is for a full frame 5"x7" pinhole camera and I want it to as sharp as possible this no burrs or oblong openings

Click to expand...

You'd want as thin a material as possible - a .2 mm (.008 inch) hole in a .2 mm sheet is a rather cylindrical thing. Beer cans are about half that. If you can make the hole by punching a nipple in the sheet and grind away until you have a hole, your thickness to diameter ration will probably be much better. Your grinding stone has to be extremely fine to avaid a jagged edge.

psmithp said:

You'd want as thin a material as possible - a .2 mm (.008 inch) hole in a .2 mm sheet is a rather cylindrical thing. Beer cans are about half that. If you can make the hole by punching a nipple in the sheet and grind away until you have a hole, your thickness to diameter ration will probably be much better. Your grinding stone has to be extremely fine to avaid a jagged edge.

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PS the material is so to speak immaterial, any will do.

For me dimple and sand works really well, using brass. You can see under a microscope that I get nice round holes with a sharp edge. Also can use the microscope to measure hole diameter... with some trial and error you do get a very good "lens".

I also want to add: precision control of all variables is not where pinhole photography is at. Dimple and sand, it takes maybe 5 minutes to make a whole and you can try and test it with a paper negative in less than 30 minutes... so trial and error is rather effective

Agree but especially for 35mm film: if your pinhole is too poor you may loose interest before you get bitten by the bug

eli griggs said:

I'd like to know others thoughts on making appatures out of brass, copper, gold alloy and silver, American coin of 90%, some 40%, sterling and some fine, 9999.

I have plenty of copper and brass on hand, in different thicknesses and a small piece of dental gold, a filling of about 12k.

The silver types listed above are also nice too work with

I also have jewelers tools, etc for working these metals and I want advice on which metal is an ideal ductile material that will allow a smooth, round hole, by whatever method folks have to hand.

I can blacken all but the gold, with Liver of Sulfer but my biggest concern is how round a hole will each make and how thick the metal should be.

I have a good micrometer, so thickness can be measured.

This pinhole is for a full frame 5"x7" pinhole camera and I want it to as sharp as possible this no burrs or oblong openings

Click to expand...

that's a good question. For pinhole thickness there is very little research, while pinhole diameter has been researched to death. There is an optimum diameter and it is not the smallest but optimized for contrast(not resolution).

eli griggs said:

I'd like to know others thoughts on making appatures out of brass, copper, gold alloy and silver, American coin of 90%, some 40%, sterling and some fine, 9999.

Click to expand...

I have a roll of pure silver that is .003" thick. A jeweler can roll it out for you. I think any thinner is very difficult to work with. I have a 50x projection microscope, and I have made gauges that are 50x bigger than increments of .001", which I can compare with what I have on the screen. I use a needle to make a hole that is too big, then I whack it using a polished peen hammer on a polished anvil to reduce it to smaller than what I want. Then back and forth between whacking and working with the needle until the desired size is reached and the opening is free of junk. It takes time, and it's tricky to find the image of the hole, but possible.

The metal is now super thin, and the hole has a tremendous clear image circle. These holes make images that a friend of mine calls "too damn sharp". They can produce incredibly rich diffraction analysis of light that falls on them.

Dominique Stroobant makes his pinholes by electro etching. That's a great idea too. Then you could use .001 with relative ease, I would think. But it's pretty high tech. If you work in a printed circuit lab, it would be worth trying.

If the metal has a significant thickness your hole will be a tube, and thus the image circle will be constrained and the diffraction effects will be irrational. Pinholes made well are capable of amazingly fine quality images.

Larry Bullis said:

Pinholes made well are capable of amazingly fine quality images.

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And the bigger the film, and wider the angle of view, the more so.

Thanks, Larry.

I have good jeweler's tools here, no mill though, and good machinist micrometers with which to check thickness and flatness there of.

I was thinking a small, but inexpensive set of precision pin gages might be handy, however, I do have some of the tiny diameter burs/endmills that Harbor Freight (and others) sells so I can check to see how well I can cover the pinhole sizes I make.

I need to test how black Fine, Sterling and Coin silver can be built with Liver of Sulfur.

I do find it interesting that gold is often used un-blackened or painted, but I've also some thin brass that can be used as a pinhole support for a very thin silver or gold foil.


Cheers.

If the edge of the hole is very thin, reflectivity is only an issue on the flat surface toward the film. I used to use black masking tape to cover that surface of my brass shim pinholes, leaving only about a 1 mm square of bare brass around the hole.

painting with musou darkest black. tested multiple blacks on scura cams. its like day and night compared with other dark blacks. also tried to darken velvet. musou non waterproof but quite!