industrial limit switches commonly use a packaged photodiode or phototransistor mounted in a plastic housing. Break the plastic away and you have a device to use. IR LED's are found in old remote controls. Almost any of these will be fast enough for checking camera shutters.
The counter approach is a good one. Old counters can be found at electronics flea markets for about $20-$30. A 20 MHz one is very slow by today's standards but fine for 1/1000 sec (1/0.001 MHz!) shutter speeds. For an oscillator- get a 10 or 20 MHz one and add a few cheap CMOS chips to divide by 100 or 200 to get 100 kHz.
Last edited by spark; 05-14-2009 at 12:11 PM. Click to view previous post history.