Sound Card Shutter Tester Questions

[Todd Barlow]

Two questions for anyone who has used a DIY sound card shutter tester for leaf shutters.

1) When you test the shutter of a leaf shutter what aperture do you use?

2) Where to you measure on the graph? I have attached 4 screen shots (from the Audacity software) showing the area I used to measure the the shutter speed. I would appreciate your feedback on where I took my measurements from.

I was testing some C330 lens shutters, the screen shots are from the 105mm.
-None were fast
-Very few matched the markings on the barrel (exception was the 105mm)
-Fastest and slowest had the greatest deviation (1/3 to 1 1/3 of a stop slow)
-Markings of 1/15 to 1/125 where found to be slow by 1/3 to 2/3 of a stop.

As always thanks in advance!

Best regards

Todd

 

[ic-racer]

Two questions for anyone who has used a DIY sound card shutter tester for leaf shutters.

1) When you test the shutter of a leaf shutter what aperture do you use?

For some reason I could not pull up your graphs so I am not sure of your technique. But I can say that even though leaf shutters 'efficiency' changes with aperture (lets in relatively more light at small apertures), the actual 'speed' does not. If your graphs look like what I am thinking of, your upslopes and downslopes should be steeper at a small aperture. The measurement across the base should be the same irrespective of aperture.

 

[Todd Barlow]

Thanks for your help and response, if you want you could PM with an e-mail address and I can sent the graphs to you for your comments.

Thanks

Todd

 

[RobC]

The graphs are contained within a word doc. right click and use save as to save the file locally and then open the doc. I had no problem.

I don't know how your lenses work exactly but if they have an aperture and a shutter, then if the shutter opens fully and the aperture is not wide open, then the click of the shutter being fully open may happen after the aperture has been fully exposed. And when it closes, there would be some elapsed time before it had closed down to the aperture size. I would therefore suggest that testing with aperture wide open is likely to give most accurate results for timing test, but it would really depend on the actual sequence of events when you press the shutter release. e.g. does the aperture also have to close down or are the shutter and aperture the same. i.e. the shutter and aperture are not two separate mechanical devices.

[edit] and there is elapsed time as the shutter opens and closes when the shutter is not fully open or closed, so the time between clicks would be longer than the given shutter time. Basically what you are attempting will not give you exact results and unless you know the exact specifications of how its supposed to work, your tests will at best be ball park figures which may give you false concerns. I would get it checked by an expert if it seems to be faulty.[/edit]

 

[David A. Goldfarb]

I assume you're measuring light rather than sound, using a photocell and amplifier circuit attached to a sound card input.

I think your graphs look right, but for the shot at 1/500 sec, f:3.5, I'd measure the peaks of the curve when the shutter is fully open. Of course the shutter is more efficient at small apertures than at large apertures, as ic-racer posts above.

The thing to do is test and be aware of the issues. For instance, if you're in low light shooting wide open and need a shutter speed around 1/15 sec, the efficiency of the shutter can make a difference, but if it's on the slow side, that might compensate for inefficiency.

 

[petrdvorak]

What photo transistor did you use? I found out that those infra ones sold in Radioshack are too slow and unreliable, their speeds vary quite a lot. I have a pair and they show very different readings. Mine were not good for anything faster than 1/125s IIRC.

 

[John MacManus]

Hi Todd

I am using Audacity/photo cell to measure a focal plane shutter on a Speed Graphic. I use a Schneider ApoSymmar on the front and its shutter for comparison. I use the lens wide open f5.6.

I get action profiles like your first one, 1/30 @ f3.5. I measure peak rise to second peak bottom. I get “expected” times on the Aposymmar at ½, ¼, 1/8, 1/15, and 1/30. Any speeds greater than this fall off and I get my 1/500 time like yours, but I’ve never seen shapes like that. I always have a down spike.

I am wrestling with this at the moment. I do get similar times with the lens shutter and the FP shutter at 1/30, 1/125, 1/250 and 1/500, so maybe absolute times at all shutter speeds with such crude apparatus is not possible. Relative speeds may be all I can get.

I am considering the $2 CDS photocell I have just doesn’t react fast enough. You might find the info on
http://www3.telus.net/public/rpnchbck/shutter speed tester.html of interest.

Have you seen the use of TV screens or audio turntables for shutter testing eg https://ritdml.rit.edu/dspace/bitstream/1850/1487/1/ADavidhazyReport03-30-2006.pdf

Keep at it … best wishes … John

 

[Lee L]

Todd,

I opened your .doc file in openoffice and saved as a .pdf, then reposted so people who don't have MS Office can view it. Let me know if you want it removed.

I'm over my quota so it won't upload. I can send the .pdf to you if you pm me with your email and you can post it yourself so others can see it. Or you could download openoffice and do it all yourself.

Lee