| Author | Message | ||
     Aphototaker Tinkerer Username: Aphototaker Post Number: 64 Registered: 12-2009 Rating: N/A |
Oh crap, I sent so much time writing my post regarding this that I missed this thread. Anyway, I will repeat that post here so that we keep this thread as the main one. So here goes. I had wanted to check the accuracy of some recently acquired film cameras. They have horizontal traveling focal plane cloth shutter. After going over some online tutorials and DIY project description, I started off with a very basic and reasonably accurate shutter speed tester. My current hardware is a IR detector diode (D1) in series with a resistor (R1) and a 3 V dc battery (V1). The drop across the resistor is put as input to a line-in socket of PC and I record the signal on that input in Audacity on a computer running Debian Linux. The value of R1 is chosen to limit the value of current flowing through the loop to valid a valid value (I use 3.9 KOhm) and V1 = 2.8 V (2 NiMH batteries in series). D1 is from the usual IR emitter-detector pair available at any electronic hobby store. V1 is chosen to be 3V to get reasonably good voltage across the line-in socket. Now, the problems is that the rise and fall time of D1 are not fast to measure speeds faster than 1/1000. So till those speeds, one can more or less measure the shutter speeds reasonably well. I have mounted D1 on the base of a black film canister. I have cut the canister to make it around 1 cm in length and position the canister behind the camera's shutter with the back open. A pair of cables (audio speaker cables, nothing fancy, terminated with a 3.5 mm male connector) take the signal from across the resistor to line-in of a PC to be recorded by Audacity (there are other ways also to get a representative signal). The input signal is a flash light positioned in front of the camera shining through the lens. In audacity, I configure it to record at 96 KHz. Basically, higher the sampling rate, shorter the time interval that can be measure better. This works very well for speeds up to 1/250 and reasonably well at 1/500 and 1/1000. I can tweak the sensitivity of the line in mic to increase or decrease the amplitude of the waveform being recorded (useful at different speeds). The main problem here is the response time of the diode used. The diode usually available at hobby stores has a response time which is actually a bit slow to get more accuracy for speed ranging from 1/250 and upwards. I am next trying to get a faster diode. Apparently the ones used in optical drives are better. But that is for the second version of the hardware. I know the details are sparse here. But circuit diagrams are easily available online. If anyone wants details, I will be happy to share. I am also hoping to make a detector with two diodes so that I can measure the curtain speeds as well. |