![Filmomat Photoplug smartphone shutter speed tester ( free APP download required)]()
The worlds first and only optical Shutter-Speed-Tester.
Buy the plug, download the app (for iOS or Android) and start making precise exposures today.
Instructions here:
https://drive.google.com/file/d/0BxEX-OlKQPG9T2pIZ2FRc1dVWl9WUzFUUC1xWE94WGF5UlpN/view?usp=sharing