Diy pentamirror blueprint

OK, so I built it without the penta-mirror to ground glass, but rather: projecting on a solid white screen tabletop. One 45 degree mirror points the vertically oriented lens at the scene and a peephole on top lets you view the projection screen tabletop just like a walk-in camera obscura room.

The solid white screen makes a much brighter image than translucent ground glass without the need for covering yourself in black cloth and the peep hole lets you at least partially correct the upside down look, which was very disorienting. The peep hole is not very satisfying compared to a large ground glass but the best use is to place a cell phone camera on the peep hole. It's also not very satisfying to watch the phone's screen but the photos you can capture are very captivating shallow depth of field "tilt-shift" / lensbaby / lomography images.

The technique can be gimmicky lensbaby shots but can also be used in a serious way for selective focus as in a shallow depth of field portrait lens with soft dreamy background. An angled plane of focus can be goofy lensbaby kitch but can also be used to place emphasis on select parts of a scene in pretty extreme ways. And I think the image quality can be pretty nice, using oddball old lenses. This build uses a cheap little old broken telescope lens with an 18" image circle but I've got another huge old movie projector lens which makes about a 6-inch image circle of very fine quality. I hope to build another camera with that which works with cell phone viewing and will be much more portable. The current build sits on a rolling cart, though the basic 18" black box cube can be toted around.

I believe I can get much sharper and more contrasty image than this early test. Note the extreme twisting of the plane of focus.

The basic 18x22" black box camera sitting on a rolling cart. 45 degree mirror on the top, with the vertically oriented lens projecting onto the tabletop below. A peep hole near the lens lets your cell phone see the image.

The white screen inside is hanging by 4 ropes which go through drilled holes and are tethered off on screws outside. A better solution would have fishing pole reels to adjust each rather than tethering. An even better setup would be a potentially complicated pulley system that brought all the fishing reels together in one place on the top and had a master reel for adjusting overall focus distance using all 4 ropes together.

Focusing a traditional large format or tilt/shift camera like this is complicated, slow and counter-intuitive. Focusing involves turning numerous knobs and dials in sequence, then going back through the sequence to fine tune. The truly ideal setup would be to bring all those ropes and pulleys to an airplane pilot's steering wheel to make those 3 dimensional adjustments intuitive.

Get a good lens and hook up a DSLR and this could take some extraordinary images. Unless you are doing huge prints this setup should be able to take some extraordinary images on a cell phone by utilizing inexpensive old odd-ball lenses. I've experimented for years with how to use these old lenses with relay lenses and whatnot and I think this is the most useful system yet. The image quality projected onto a good screen should be great for digital capture, making full use of the lens' original capability.

Another couple technical details: The peep hole is located in front and left of the lens. This means the phone is pointing at the screen at an odd angle which could mess with the focus alignment and geometric trueness. Not a problem if it's easy to fine tune the focus with a pilot's steering wheel.

The way it works is you stand on the left side facing away from the subject (because the image is inverted) and use your right eye (or right hand to operate the phone).

I've talked about tilt focus but not shift. Shift is about correcting parallel perspective for architectural photography. The 18" image circle for this camera is pretty generous, to allow for panning across the projected image till columns are plumb by panning over to the side of the image. This is a matter of how wide the angle of view is on your phone and how tall or low you can place the lens. We are getting into obscurities here: #cameraobscura