CHEM DCO: Canon Hack Emulating Medium-format Digital Camera Obscura

This is a digital camera obscura designed to give Canon PowerShots, such as the ELPH180, the bokeh of a 44x33mm “medium format” sensor. The “Hack” aspect of the name is also a reference to the idea of using CHDK, the Canon Hack Development Kit, to reprogram the camera to fix focus on the obscura screen, shoot an HDR sequence, etc.

Although 44x33mm is a bit small for medium format, there is the nice benefit that the 55mm diagonal is easily covered by many lenses designed for full-frame cameras. Thus, this unit is designed to take an M42 full-frame lens, like the 55mm f/1.4 Mamiya/Sekor pictured, and let it render like a 44mm f/1.1 lens would on a full-frame camera – despite the ELPH180's sensor being MUCH smaller. When used on CHEM, a lens generally behaves like a lens with the focal length and f/number both divided by about 1.27 would behave on a full-frame camera, no matter how small the actual digital camera sensor is.

The printing is easy, although the silver and black parts are only for printing using a two-color printer (this was printed on a Bambu X1 Carbon). You can simply print the three other parts, and none should need any supports nor postprocessing unless your filament is somewhat translucent, in which case black paint can help. The screw is used to lock the PowerShot in place via its tripod socket. Notice that CHEM has its own tripod sockets and even an Arca-compatible foot.

The BSI screen is critical, and it can take some experimenting to find a good material. Vellum or diffusers usually work best, and you literally tape the screen in place as shown. Realistically, don't expect more than about 1MP effective resolution due to the screen diffusing the light.