[HOW-TO] ExposureTime / ShutterSpeed

How set minimum ExposureTime / maximum ShutterSpeed.

Dear Developers, I working on a SkyCam for SolarPowerPredictions. I created some examples…

libcamera-jpeg -o shutterspeedxy.jpg --shutter xy

Ironically there comes a point where the exposure increases again instead of continuing to decrease.

However I just would like to reduce the exposure time further? How can I set the maximum possible, do i need to add more settings?

Thank you!

[davidplowman]

There are a couple of problems here. Firstly it looks like you might be using the old PiCamera interface? The Picamera2 interface uses a set_controls method to pass particular camera controls, e.g.

camera.set_controls({"ExposureTime": 100000, "AnalogueGain": 1})

The next thing is that cameras have quite a deep pipeline, especially for exposure and analogue gain (as even the sensor takes several frames to deal with them), so it will be quite a few frames before those controls have the effect you want. Though you can change them frame-by-frame, so the long-ish delay is only for the first change to happen. (The other alternative is to stop the camera, request the values and then restart it. You’re then guaranteed that the very first frame will have to values you wanted, but the whole stop/start procedure is a bit slow.)

I’ve wondered about providing a function which says “capture frames at these different exposures/gains”. It would take a while for the first one to arrive, but then they’d come in pretty much “back to back”, (Though even then care has to be taken because nothing guarantees that the system might not drop one of them, so you’d have to sort of keep requesting them until you’ve got them all). So maybe I’ll look into that.

One more small fly in the ointment is that I think nothing actually tells you the max/min possible exposures, so asking for something smaller than is possible would end up getting stuck waiting for something that can’t happen. We’d probably need some changes in libcamera to address that, so that might be slightly trickier, or at least take longer to change.

[davidplowman]

I see you’ve posted on libcamera-apps now, so thanks for doing that. I’ve replied there, so will close this thread. Thanks!