A Low Cost Spherocam

ScanCam Mark 3.

ScanCam Mark 3 takes near-spherical panoramas with a Sigma 8mm fisheye lens that covers 152 degrees vertically. To keep them out of sight, the bulky parts of the scanner (circuit board at front and motor plate at rear) rotate along with the lens, which is tilted up 3 degrees. A cable wrapped around the axis carries power and USB lines from connectors mounted on the base plate. The electronics are from a 600 DPI Umax Astra 3450 scanner, whose CCD is 28 mm long with 5400 pixels. The lens’s image circle covers about 4300 pixels – roughly 12 pixels per degree, or 35M pixels in a 360 degree image. The drive ratio is 9600 steps per turn, allowing a minimum scan time of less than a minute. I was lucky enough to get the lens, an old manual focus model on a Minolta mount, for only $250, so parts for Mark 3 cost under $450. The “camera body” is a Minolta-to-C-mount adapter, slotted at the rear to accept the plastic lens cone sawed from the scanner carriage, which is glued in place with Plastic Weld. The cone houses a simple electrically operated shutter for dark calibration and supports the CCD board. There are rubber strips between the board and the cone so that I can set infinity focus with the mounting screws. The CCD board is currently shrouded in black vinyl tubing and electrical tape – ugly, but dark. Since this picture was taken the lens has been fitted with a 3mm wide vertical slit aperture, to reduce flare, and the white ribbon I/O cable has been replaced with something that better matches the USB impedance requirements.