I installed a brief (3-4 days) camera obscura locally as an experiment. Initially I started with a variable iris, about 1.25-1.5" in a 33'x24' or so room. 90 degrees away I put in a 4m (13') zoneplate made my a list member (I won't name unless he volunteers, so he doesn't get swamped with requests).

There was a portable wall, v-shaped with a 90 degree corner in the gallery. For optimal use at the zone plate side, it was in the way of the main aperture. The sun was able to illuminate the zoen plate, so at sunset it looked like a flashlight spot. So we covered it up.

It became overcast, and I tried a 0.25 diopter (4000 mm) 40 mm diameter (f/100) lens, and despite similar or worse f-number compared to the open iris, the lens brightened and sharpened things in a much better way. I was sure that DOF would be terrible so I didn't try it until the last day. It was actually good.

I did not want to spend time with a learning curve shooting with film in the dark, so I just set up a digital camera. Phone cam did not have enough sensitivity. I shot 15 seconds @ f/5.6 which was EV1 (I think I was on ISO 100, but didn't check). I had to brighten images in GIMP, so the light level was still lower than EV 1.

Here are two images.

The right angle wall was moved in front of the f/100 lens. If you look carefully you can see how the flat building was bent into the 90 degree corner and the 6" thick wall ends are visible.

An inverted view is also included for convenience.

Cars, bicycles, runners and a person with a limp were all interesting to watch moving by. A tree in front of the gallery was macro, larger than 1:1.

Cars seemed to be affected by a 'visual Doppler effect', their speed changing and seemingly moving around the room as the image changed walls. The lens also projects aberrations at the far end of the room.

It was well received, and they want to do it again this summer during their art camp.

Attached files