| Author | Message | ||
     David_nebenzahl Tinkerer Username: David_nebenzahl Post Number: 158 Registered: 12-2009 Rating: N/A |
I'll talk about the one I built, and hopefully others will add their own observations and experiences. I built a fairly simple but very accurate shutter-speed indicator. It's a small microprocessor-based unit, in a small project box about 1x2x4 (inches). It uses a SX-28 MPU, an easy-to-program 8-bit chip, complete with memory, similar to the more well-known PIC line of processors, first introduced by Ubicom, then taken over by Parallax (currently owned by some other company, forget the name: they're still available). The tester consists of the SX-28 chip, a phototransistor used as the light sensor, an oscillator crystal, a LCD display (1x16 characters) and a few other components (including switches and a 9-volt battery). Total cost as I remember was less than $40. (Of course you need a programmer for the SX too; I borrowed one to program it.) The program is pretty simple, consisting of the following: o Sit in a loop waiting for the phototransistor to sense light o Start the timer counter, wait until it goes dark again o When it goes dark, compute and display the elapsed time in milliseconds There's some de-bouncing code and some display routines (plus hand-coded multiply and divide routines), but that's basically it. It shows you how long the shutter stayed open in milliseconds (1 second = 1000, 1/25 = 40, etc.). I know it's accurate to at least +/- 0.1 millisecond, as I tested it against a known good timer circuit with a microsecond resolution, so it's plenty accurate enough, at least for the cameras I work on. I'd be curious to hear about anyone else's DIY shutter speed test strategies. I know about the sound-card tester (basically a more primitive version of mine), using a TV set, various tricks with turntables, etc. |