On Fri, 26 Oct 2012 19:23:06 -0700, "Zane H. Healy" <healyzh at aracnet.com> wrote: Several years ago I built a simple shutter speed tester with two phototransistors on a piece of perfboard. It is meant for 35mm cameras and has the phototransistors spaced 18mm apart, 9mm from the edges of the frame, so that they are equally spaced from the centre of the frame, half the frame width apart. The transistors have 10k collector resistors and are fed from a 4.5V battery supply. The collectors go to the tip and ring of a 3.5mm stereo plug, which plugs into the line (or microphone) input of my laptop. I strap the perfboard behind the shutter of my camera with rubber bands and point the camera at a lamp. I then use Audacity to record the output of the tester when I fire the shutter. If you display the recorded waveform from a focal plane shutter, the two channels will show when the shutter curtains pass each phototransistor and you can then easily work out the shutter speed. IIRC it will also show if a curtain is slow near one end of its travel. Obviously, it also works for blade shutters, both traces will then show the same. Also obviously, the transistors are fitted behind holes in the perfboard so as not to foul the shutter curtains :) You can find several versions of this design on the net by Googling. It works quite well. You will probably find that speeds down to about 1/250 are correct, and 1/1000 will be quite badly off and cannot be made correct. /Jonas