People are making this way too complicated. If you just want to use your soundcard or a scope or some other input, then all you need is a photodiode/phototransistor and a resistor. And a AA battery. I made one like that and used it a lot until I made my microcontroller-based one. It works fine. Note that the simplified diagram shown will dump a square wave into your soundcard, but for the short speeds typical of shutters, it shouldn't be a problem. Mine uses a capacitor and a pot, so it actually outputs two spikes, one when the shutter opens and one when it shuts. Using audacity you can just highlight the distance between the shutter opening and shutting, and it reads out the time value of the highlighted selection in seconds at the bottom of the screen.