An easy DIY lightproof drain for a pinhole camera?

I’d like to make a homemade pinhole camera to make solargrams, which require long exposures while exposed to the elements. I’ve tried this in the past with varying results, but one thing that has been consistent is that water gets into the camera and messes with the photo paper. The occasional raindrop will hit the pinhole and, once inside, there is little opportunity for the liquid to escape; it can’t evaporate faster than new water enters. I tried replacing the pinhole with a thin piece of painted glass, with the pinhole being a clear spot in the paint, but that didn’t work very well either, since the glass caused refraction that spoiled the pinhole effect, and the paint weathered and lost opacity.

This time I was thinking of making a camera out of an aluminum soda can. I’ll cut the top off the can to insert the photo paper and reseal seal it with the bottom of a second can, stretched and inverted to slide over the top of the first can. But I wonder whether there is a way to make this camera have a light-proof drain to let accumulated water out of the system. My first thought is to cut the bottom half inch off of several soda cans and punch a small hole in the bottom of each piece, then stack them with the holes rotated 180 degrees apart, then to punch a hole in the bottom of the camera and slide the stack over that. I’d spray everything black inside before assembling the stack. It seems like water should be able to find its way out by gravity, but light would have trouble making it around all the bends.

What do the teeming millions think of this approach? Are there already ways to let water out of an enclosure without letting light in that would work on something the size of a soda can?

How about including a packet of silica gel as a drying agent?

I would make a hole at the lowest part of the enclosure and cover it with a black cloth. Water should be able to seep through it.

But maybe the problem isn’t water entering the pinhole, but moisture condensing inside the enclosure? If so, it’s probably caused by radiative cooling of the enclosure. (Water will only condense on a surface that is cooler than the surrounding air.) If that’s the case, you can minimize it by covering the enclosure with some type of insulation or a shade.

Over a six month period, the cameras retain a macroscopic amount of water - like 15-20 cc - so I think that silica would be overwhelmed, or would swell way up.

I suppose condensation could be playing a role, but would it result in a net accumulation of water over time?

Yes if it’s not completely air-tight.

Your original idea of staggered holes should work too. If I understand correctly, you are talking about multiple surfaces, spaced some distance apart, with holes that don’t line up. I’ve seen a design like that used as a light-tight air vent. I’m not sure how well water would flow through it though.

Another design I’ve seen is a twisted (coiled) metal tube. Though to act as a water drain it would need to be a downward incline all the way.

I still think black cloth would be the simplest way to do this.

Ah. I didn’t realize this was such a long term project. What about a small fan directed across the pinhole to deflect most of the incoming water?

Or a fan ducted into the camera body creating a positive pressure blowing water away from the pinhole and incidentally clearing dust or other obstructions.

Glue a microscope coverslip (0.1mm thick) behind a hole in the camera body. Give it a spritz of flat black paint inside the box and poke a pinhole through the paint. Minimal refraction problems and the paint is protected from the weather.

What I would do is use compressed, dry air, to slightly pressurize the camera. This will prevent any moisture from accumulating within and also prevent any rain from coming in.

Another option would to keep it hot, like 20-30 degree above boiling which will also prevent condensation. Don’t know how the film would handle that long term though.

So, back to air. You’ll need a source, lines, and a regulator. Compressed dry air from a supplier might be best as if you use a compressor you’ll have to dry it via desiccant plus vibration isolation. If this pinhole is as small as I think it is, the tank might well last for awhile as you’ll only need to be at a PSI above average (storms can change this) and a relatively low flow rate.

Why would you say that ?

For 20 cc (20 g) of water, you’d need about 60 g of silica gel. Make it 100g to be safe and you are all set. Also - silica gel does not swell.

From - Types Of Desiccants | USA Emergency Supply

I wouldn’t expect much water to get in through a well-made pinhole camera. The aperture is typically about a third of a millimeter or smaller in diameter, and it’s hard to see water getting in through that unless it’s a downpour.

https://en.wikipedia.org/wiki/Pinhole_camera

There is species of Nautilus that has a pinhole eye. The way it keeps things from getting in is by having a narrow trench filled with waving cilia that constantly sends a stream of water over the pinhole. The equivalent for our air-based camera would be to use a blast of air across the pinhole, as already suggested, or perhaps to pressurize the container so that there’s a constant stream of air coming out.

You can color in all but a pinhole spot on a very thin piece of glass or plastic, or placing such a thin piece behind the pinhole (as also suggested above).

If your problem is due to condensation – as I expect, since I thin water getting in through the hole unlikely – you can use heating to keep the condensate out. Wrap heating tape around the camera, or do something similar to keep it warm. This will also help evaporate out water if it DOES end up coming I through the pinhole. It’s work better than dessicant, although it means your camera would have to be near a power source.

If it’s just 20 mL of water, you wouldn’t even need to drain it completely. You could just have your camera draining into a reservoir below it, with the whole thing completely sealed.

That said, your idea of staggered holes and black paint should work just fine. And you’d probably want the interior of your main chamber to be completely painted black, anyway.

I am making multiple cameras and setting them up in remote locations to take six-month exposures on photographic paper. Compressed air or heating elements or anything requiring power or ongoing maintenance is not an option. Each of these cameras costs me about a dollar to make, not counting the cost of the soda cans, and I’d like to keep them cheap. I will try an add-on double bottom that contains silica gel, with holes in the camera bottom to let water weep into the gel, as one option.

As I said in the OP, I already tried a glass window with a pinhole in paint, and optically it was unsatisfactory. And yes, I used glass coverslips, because that was the thinnest glass I could think of, too. I would expect another attempt to be more difficult, since I would be trying to seal a flat coverslip to the curved wall of the aluminum can camera body, instead of to the flat camera face I used previously.

I’ll try my offset-holes-in-nested-bottoms as another option, and I’ll see if I can rig up a coiled tube drain as well. A bit of black fabric wicking plugging the outermost hole seems like a good idea too.

Yeah, but which side did you paint? And was the pinhole perfectly smooth around the edges? Adapting a flat slip to a curved surface is easy if you mount it in epoxy putty.

I used a needle to deposit a tiny drop of hairspray on the center of a coverslip; the coverslip was painted with matte black rattlecan primer, including the edges, and the hairspray dissolved with water to create a pinhole chip in the primer. The pinhole appeared quite round and comparable in size to the physical pinhole apertures. The coverslip was glued to the inside of the camera body with black silicone, paint side in. After six months, the image was blurred and overexposed compared to the pure pinhole images, albeit not wet or moldy. The primer was faded to charcoal gray and probably no longer 100% opaque. The external glass surface of the coverslip was dusty, too. All in all, I’m inclined to try a pinhole with water diversion rather than a glass ‘window’ that will get dirty/have internal reflections/maybe not be as opaque as I want.

OK, I’ve got two cameras made with reservoirs at the bottom to hold water away from the photo paper.
Two have bottom reservoirs filled with ~3/4 cup of silica gel.
Two have bottoms with three layers of offset holes, and two have bottoms with just two offset holes with synthetic fabric or a Scotch-brite pad wadding in there to block the light. Without the blocking material, two offset holes don’t work to keep light out.

I will try to get them all set up in time for the Solstice tomorrow, with the plan to take them down after the Summer Solstice next June. We’ll see how they do.

[Bolding mine]

Couldn’t that be motion blur? How well was the camera stabilized? I would imagine that wind and rain would move the camera causing motion blur.

Is/would be your camera facing straight up? If not, maybe the pinhole could be recessed so that less/no rain could hit it. If you can keep out all moisture except for condensation/humidity the desiccant packets should keep moisture low enough.

ETA: A quick look on Google shows me other folks are making solargrams with pinhole cameras. Find out what their set-ups are.

Maybe put it on its side and use a mirror at 45degrees?

I recall “how to make a pinhole” for spatial filter for holography, the technique was to put a piece of tinfoil against glass and use a pin to make… a pinhole. then remove the glass and you have a fine hole.

For the teeming millions who were waiting to find out how this all came out…

Of my eight cameras, none had any moisture in them! All the photo papers were dry, and there was no evidence of old water intrusion. Apparently the soda-can construction is the key. The pinhole alone doesn’t seem to be enough to allow water to enter. My older cameras must have been leaking along the seams despite my efforts to seal them, and/or my pinholes were smaller this time around. This was after an unusually snowy winter and a rainy, flooded spring here in my part of the Midwest.

The light-proof drains worked inasmuch as there wasn’t any light intrusion into the camera bodies, but they probably weren’t necessary. I didn’t weigh the silica gel before and after, but its gross appearance is unchanged.

So for round 2, I’ll probably skip the reservoir/drain entirely, and just go with a sealed can for simplicity. A 16 oz soda can is just about the perfect size to hold a 4x6" sheet of photo paper.

Pics or it didn’t happen…