|Favorite Classics Camera & Repair Articles Test Equipment Shutter Speed Tester|
Theory: A capacitor stores voltage. The magnitude and duration of the voltage applied determines amount stored. For a set aperture and light level (magnitude), then the faster the shutter speed (duration) the less voltage is stored.
Gather up all the components listed on the circuit drawing and assemble as shown in the pictures. This is just my own personal physical arrangement, nothing sacred. Feel free to modify it anyway you desire. The power source voltage, resistor value and capacitor rating are all variables also. The values shown are from Tomosys first book. Different values will change the range of the shutter speed readings. You should seriously consider purchasing Tomosys and Romneys books. They are a good read. Ive seen this same circuit with different value components in basic electronic experiment books.
I use 3/16" thick light baffle material on the tester surface that contacts the cameras focal plane. All extraneous light must be blocked.
Use the Adjustable Light Source set at a known EV and at a standard distance from the camera. The light brightness and distance from camera must not vary. Calibrate by recording the voltage readings of a known accurate shutter at all its speeds. Better yet, compile data from several known accurate shutters to be even mor accurate.
My standard setup is to set the Adjustable Light to EV 13, for camera at a focal plane distance of 8" with lens installed and aperture set at 3.5, room lights off .
Tomosy also shows how to turn a Commodore 64 into a shutter tester, but I havent tried this... yet. What I am working on is using my laptop and a parallel port adapter to do apertures, shutter speeds, curtain speeds and EVs. Im not very good at programing so this may take awhile.