View Full Version : Testing shutter speed using audio?

13-Sep-2009, 07:29
I have a nice fujinon 150mm lens mounted in a copal shutter. I'm pretty sure the slow speeds are way way off but would like to test it.

Has anyone ever tested a shutter's accuracy by using audio analysis? I don't have a shutter speed tester and I don't want to buy one, nor do I want to waste half a dozen sheets of film trying to find out what the real shutter speeds are.

What I mean is, set up a microphone near the shutter, open an audio recording program, set the shutter then trip it.

My idea is that you should be able to hear the shutter when it opens, operates and then closes, and you can measure the audio signal very accurately down to thousandths of a second.

Will this work or am I missing something?

13-Sep-2009, 07:34
Why not? I think I've heard of people doing this.

13-Sep-2009, 07:51
This definitely works and it is pretty accurate if you have some digital audio experience. I have done it quite a few times.

Ivan J. Eberle
13-Sep-2009, 07:58
Since you apparently already have a computer you could easily try this using a freeware sound editor like Audacity, which will record/graph the sound and time it with great precision. Zooming in to analyze it should allow you to infer something about the rise and fall times of the shutter opening. But for just a very few dollars and an hour or so of your time, you might consider buying a fast-rise photo transistor to make a "sound-card shutter tester" which also uses the microphone port of a laptop but triggers with light, not sound. Google this term and you'll find a half dozen tutorials. I built the simplest of these, using only a $13 photo-transistor, a AA battery holder, a small project box, the plug end from a defunct set of ear buds and a daub of 5 minute epoxy. Total cost of under $20 for something that works very well indeed with my MacBook Pro.

13-Sep-2009, 08:01
I have done it but at faster speeds, it is difficult to find the exact opening and closing points because the tripping mechanism makes noise also. Slower speeds it works fine. To test the fast speeds I tried putting some 'white noise' behind the shutter and putting a cardioid mic in front of the shutter to see if I could catch the sound, but the problems with sound waves (unlike light waves) is the frequency of some of the sound passing through the shutter is lower than the opening/closing speed. So you don't get a good wave. You get a complex waveform that is hard to analyze.
A high-frequency pizo source might work.

Rather than using a mic and sound, you can use light and an optical sensor. A very simple electrical circuit can turn the optical output into a sound input for you sound card. There are a number of web sites that tell how to do this.

13-Sep-2009, 14:21
i never use high shutter speeds for large format, i've got some 35mm stuff for that. the slow speeds are way off though and i spend all my time down in that range so i thought i should check it out.

i have a nice shotgun condenser mic so i think i'll use that.

i think i'll give it a go, thanks guys, will see how it works out.

Greg Lockrey
13-Sep-2009, 15:53
It's close enough for photography work. :)

13-Sep-2009, 19:59
A more fool proof way of testing the shutter with audio would be to run a fixed frequency tone into a LED, and use a photo sensor on the other side of the shutter to receive it, hooked to a mic or line input.

Any good audio software (or competent o-scope) should be able to measure the duration.