Add a Raspberry Pi camera to your AmScope desktop microscope. Fits exactly over the eyepiece with no additional hardware required.
Since every eye piece is slightly different, you'll need to experiment a little to find the best place to mount the Raspberry Pi camera board. When you find the perfect spot, burn a couple of holes in the plastic with a soldering iron and screw the board in place.
More details here: http://hackerfriendly.com/amscope-upgrades/