Quote Originally Posted by BetterSense View Post
I have 2 homemade shutter testers, an analog one that uses a phototransistor and a digital one that uses a photodiode and microcontroller. I use external sources of light for both. Any concerns about the unevenness of the shutter tripping can be taken care of by putting the measuring photodiode at approximately the film plane, which you should be doing anyway. Since the photodiode is approximately a point source, any concerns about the shape of the shadow cast by the shutter are taken care of. You are welcome to worry, I suppose, about the light pulse being not-exactly-digital due to lens effects from leaf shutters, but I'm sure not.
I did the same with mine. I have an IR photodiode mounted in a plastic plate and I place the camera with the back open onto this which places the diode at the film plane (or close enough). I use it on my kitchen worktop directly under a light fitting and I have found it works just as well with or without a lens fitted (35mm SLRs). It works fine with in shutter lenses too.

Mine has a 7 digit (7 segment LED) counter and a 100kHz oscilator which is gated by the photodiode. It gives the shutter time in milliseconds to the nearest one hundreth of a millisecond.