Well, it’s time to verify if the shutters speed of my cameras are compliant to the specifics declared by the constructors. This is a periodic check that every photographer have to run to assicure that his cameras (expecially the older) are always reliable. I have got a Nikon FE, an 801-s and a Mamiya rz67 pro2.
The best method to measure the shutter speed of a camera is using a light beam. It have to travel through the camera body and the shutter when the latter is released. The time during the shutter is open is than registered and precisely measured. How to do that?
I’ve made with just few electronic components a signal generator that produce a pulse at the beginning when the shutter is opening and another when it is completely closed. The pulse are registered by the PC through the sound card (line-in input) using Audacity (the best free sw for audio recording). With Audacity is possible to measure the time passed between the two pulse and calculate hence the amount of the error of the shutter speed (or better find if the shutter has to be revisoned).
In the image above the simple schematic. A phototransistor bpw40 (I chosed this because is simple to find and has enough sensitivity in the visibile zone of the light (< 900nm). A resistance, a ceramic capacitor and a voltage source (1x AAA or AA 1,5v or 9v battery- as you wish) and a jack 3,5mm stereo (for simplicity) that will connect the “gadget” with the line-in plug of the sound card on pc.
above how I’ve mounted all teh stuff (in a dia box !). Notice on the bottom of the image, the black caps with a small hole in the middle (2mm). It permit to measure with more precision the light coming through the camera even at fast times (1/1000 sec).
In the image the Mamiya that have the lens mounted (central leaf shutter). With Nikon FE the lens is not necessary (it’s better to measure without lens).
Now an example of measure:
The frequency of sample is 384Khz. The time between the pulses is visible on ythe bottom (ie: 0,004 sec).
So proceed to measure the time of every speed of the camera and than elaborate with excel the data:
With my surprise the Mamiya have a 1 stop of overexposure at 1/400″ (the fastest shutter time permitted). For now I’m going to compensate with the aperture (-1 stop at 1/400″).
That’s all folks! Enjoy yourself 🙂