Joaquín de prada in Opensx70 5 minutes

the "jig"

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As part of my on going investigation on the SX70 I wanted to photograph the shutter operation: I wanted to know how log it takes for the shutter to open from the moment I remove the power to the Solenoid. It turns out it is a lot. For this purpose I got the amazing RX100 and built a jig to do my tests.

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It is basically a few pieces of MDF wood screwed toguether. I have a sliding platform for the digital camera and a close up lens.

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Then I process the video with Avisynth and extract a bunch of jpegs with the frame number, every frame is a ms. I have modified my arduino code to light an LED for 5ms just before and after I issue the shutter open and shutter close command. When the LED turns off, it is T=-1.

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Then at T=8 the shutter begins to let light through, this is very consistent with both the Sonar and the SLR690.

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And finally at T=82 the shutter is totally closed.

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So we can say that it takes around 48-50ms to fully open and 10-15 to close, so it definitely closes much faster that when it opens with the spring action. I have no tried to make it faster by adjusting the screw.

As a conclusion, I am happy with the results. I have made a even-slower-motion video of the whole thing for my Alpha (“Franken”) camera. 66ms lends to the shutter to archieve the f.8 fully open possition. I am baffled as to the relation of the aperture with the speed, meaning, when is a shot x ms f.8? When it reaches f.8 in x ms of time or when it, once it has reached f.8 position stays in that position for x ms amount of time?

https://youtu.be/MU2MqRjvjZs

I might be redoing the whole thing, trying to get more accurate across-the-board results. My first-gen camera didn’t work as the rest. I am thinking that maybe it lacks the flyback protection diode? Keep learning!

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