The subject of using a Arduino to do video capture/digitizing was beaten to a miserable death in the thread: http://forum.arduino.cc/index.php?topic=150237.30
I am looking for an alternative solution and I will explain why. I use a very old, obsolete Nikon Coolpix 995 camera with an inspection microscope. The reason that I use this particular camera is because there has been nothing manufactured since that approaches the effectiveness as an 'eyepiece' camera. It is ruggedly constructed with adequate resolution (2048 x 1536) and a 28mm lense thread. There are/were many lens adapters for microscopes and cameras ... and I happen to have a one. ref: http://en.wikipedia.org/wiki/Nikon_Coolpix_995
Unfortunately the camera control RS-232 and the USB 'disk' interface on this camera use a Nikon proprietary 8 pin connector that can not be obtained except as an USB disk cable. The female connector can not be obtained period. Four pins are used for RS-232 control and the other 4 pins are used for USB disk drive emulation. There is documentation on splitting the Nikon end of the USB cable and adding the wires for the serial control interface, however when the serial interface is active the USB disk function is disabled. It has occurred to me that I can attache the modified Nikon cable to a small Arduino (Nano or Teensy ??) and develop a small sketch to control the current mode and pass the signal back to the computer over a "STANDARD" USB cable. The small package could be attached to the 1/4-20 tripod mount of the camera. As long as I have to furnish power to the Arduino I might as well include power for the camera as well (wall wart).
That leaves one function that is missing: "live view" for focussing and such is provide by an additional connector that outputs a NTSC/PAL video signal. It would be extremely convenient if this signal could be passed back to the computer over the USB cable. This is particular true because I do not currently have anything that can display a NTSC/PAL signal. It does not need to be live (30 fps) speed. One to five frame per second should be adequate.
So thinking outside the box: has anyone got any ideas ??? .... a fast A/D chip .... USB PAL/NTSC converter .... give up and punt