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Author Message   Hanskerensky Tinkerer Username: Hanskerensky Post Number: 256 Registered: 05-2009 Rating: N/A Votes: 0 Posted on Saturday, June 22, 2013 - 01:20 pm:    Strangely enough, that webpage mentioned by the OP contains a link to another page : http://www.echolot-online.de/Shutter-Speed.html Which seems to be made by Lukas Fritz himself. There he mentions that for SLR's you can go only till the flashsync speed because faster will not be recognised by the acoustic system. However, IMO faster speeds should be recognised by going the optical way. Accuracy is of course another theme. This would greatly depend on shape, position and characteristics of the used sensor. For SLR's it would be better to have at least 2 optical sensors, positioned near the start and the end of the curtain travel. Even better would be 3 so that also the middle of the filmgate would be visible in the measurement. The measurement head (for 24x36mm filmframes) on my Kyoritsu Arrowin EF8000 even has 6 sensors, 3 for a vertical traveling curtain and 3 for a horizontal traveling curtain. btw Just wondering if the iPhone has a stereo microphone input ? In that case 2 optical sensors could be used and that would make this system more versatile.