Post by Stephen on Mar 7, 2015 10:39:53 GMT -5
I notice a lot of references to members being unable to test shutter speeds properly. It is of course difficult to build a dedicated tester, and it would need calibration etc.
There are commercial units made, but are expensive.
However you have the guts of a tester in front of you, the PC itself, with a suitable audio programme.
Audicity software is able to register sound pulses down to milliseconds, and can also recognise the equivalent signal from a photo transistor, sent via the microphone socket to the computer soundcard.
The trace generated will show to shutter opening and closing, and you can count the milliseconds off the scale. It needs no calibration and is strictly accurate.
The circuit is very simple, powered by a 1.5 volt battery, the transitor can be almost any npn photodiode.
The diode is set in a wooden board about 6x6 inches facing up through a hole, and the bulb placed on a bracket above the camera or shutter unit.
To use, set Audity to a sample run, and simply turn on the circuit (in dim light), and fire the shutter, close the Audicity sampling, and have a look at the trace, and work out the speed.
It will work best if the cell is centred on the Transistor, and the LED bulb is directly in line.
The LED light source can be a simple torch light, a laser pointer, or a single high intencity white LED bulb. It is best the light comes from one bright source.
The tester is accurate enougth to test each side of a focal plane shutter, to ensure an even exposure. With leaf shutters set the aperture to mid range value to get best accuracy.
Stephen
There are commercial units made, but are expensive.
However you have the guts of a tester in front of you, the PC itself, with a suitable audio programme.
Audicity software is able to register sound pulses down to milliseconds, and can also recognise the equivalent signal from a photo transistor, sent via the microphone socket to the computer soundcard.
The trace generated will show to shutter opening and closing, and you can count the milliseconds off the scale. It needs no calibration and is strictly accurate.
The circuit is very simple, powered by a 1.5 volt battery, the transitor can be almost any npn photodiode.
The diode is set in a wooden board about 6x6 inches facing up through a hole, and the bulb placed on a bracket above the camera or shutter unit.
To use, set Audity to a sample run, and simply turn on the circuit (in dim light), and fire the shutter, close the Audicity sampling, and have a look at the trace, and work out the speed.
It will work best if the cell is centred on the Transistor, and the LED bulb is directly in line.
The LED light source can be a simple torch light, a laser pointer, or a single high intencity white LED bulb. It is best the light comes from one bright source.
The tester is accurate enougth to test each side of a focal plane shutter, to ensure an even exposure. With leaf shutters set the aperture to mid range value to get best accuracy.
Stephen