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HermannSW
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Joined: Fri Jul 22, 2016 9:09 pm
Location: Eberbach, Germany
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very short multiple exposures (eps: exposures per second)

Sun Jun 02, 2019 9:51 pm

I did google and found a lot "frames per second", but no "exposures per second" hits.

In this forum I found hits for "long multiple exposure", but not of (very) short multiple exposures.

In "Raspberry v1 camera global external shutter" github repo I describe how to do very short multiple exposures:
https://github.com/Hermann-SW/Raspberry ... al_shutter

For video "speed" the number of interest is "frames per second" (fps).
Similarly I name "eps" as exposures per second (I am sure that was done before, but I found no hits on google).
Here are some examples.

Five 9µs strobe pulses 241µs apart, this is a "4000 eps frame" (1000000/(9+241)):
Image


Nine 9µs strobe pulses 116µs apart, this is a "8000 eps frame" (1000000/(9+116)):
Image


Slower, but linear capturing of flying airsoft pellet instead of radial. Taken with a 3kHz PWM signal with duty cycle 2.5% (8.33µs). For PWM the PWM frequency is the eps value as well; this is 3000 eps frame:
Image


Tbd later is capturing flying bullet from real rifle. A 375m/s bullet does move 0.375mm/µs. If an exposure every 3cm is wanted, exposures have to be taken every 30/0.375=80µs (12.5kHz PWM). The result will be a 12500 eps(!) frame (1000000/80).

Such a capture every 1.5cm would result in a 25000 eps(!) frame.

I took frames with 4µs strobe pulse length already, doing so 6µs apart would give a 100,000 eps frame ...

P.S:
Impressive eps numbers, Raspberry cameras can do high framerate video capturing only up tp 750fps/1007fps for v1/v2 camera due to the "slow" data transfer needed for each frame from camera to Pi. For high eps transfer frame time is no issue at all since the single frame will be transferred after the capturing completed. While 1007fps capturing with v2 camera is only possible for 640x75 frames, the above shown 8000 eps frame is a 2MP 1920x1080 frame(!).
bookmark list: https://stamm-wilbrandt.de/en/Raspberry_camera.html

https://github.com/Hermann-SW/Raspberry_v1_camera_global_external_shutter
https://github.com/Hermann-SW/fork-raspiraw
https://github.com/Hermann-SW/userland
https://twitter.com/HermannSW

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