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I would like to use the Raspberry pi HQ camera for astrophotography. I have read in the answers and comments on this question that I should be able to use a maximum exposure time of 200 seconds.
This is also stated in the camera guide book (pdf) on page 115:

Shutter speed
--shutter or -ss
Sets the shutter speed to the specified value (in microseconds). The upper limit is around 6000000 µs (6 s) for CM v1; 10000000 µs (10 s) for CM v2; 200000000 µs (200s) for HQ Camera.

Can somebody explain how to use 200s of exposure time? In this answer they mentioned, using sudo rpi-update is enough to unlock this functionality. But after running that command I can't see a difference between photos using the 200s and 10s exposure time.

The solution: I found it on this page.

time ( raspistill -t 10 -md 3 -bm -ex off -ag 1 --shutter 239000000 -ISO 800 -st -o image.jpg )
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    \$\begingroup\$ Glad to see you've found a solution (and came back to share it)! Please post it as an answer (and mark it as answered) as that allows people to give you credit for it and improve it if necessary. \$\endgroup\$ Commented Sep 16, 2020 at 17:08

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Personally, I would not use a continuous 200 second exposure for astrophotography.

The way I see successful astrophotographs made is with multiple short exposures, stacked in external software, or sometimes in-camera.

Stacking has numerous advantages. For one, noise performance is greatly enhanced, as the light from stars is additive, but noise, being random, tends to cancel itself out.

So, you might try (for example) taking 200 each 1-second images, then stacking them.

Some cameras (Olympus, perhaps others) have a "Live Composite" mode, which only overlays light parts of the image, keeping the dark parts dark.

Your Raspberry Pi may have enough horsepower and RAM to be able to do stacking internally. Since it runs Linux, there is software you can install on it for stacking. One that is fairly lightweight is ImageMagick, but it is fairly nerdly! But I think it would be capable of the composite stacking that Olympus (et. al.) does.

This was not done on a Raspberry Pi, but it demonstrates what you can do with composite stacking. It used 4,200 ten-second exposures.

Alpha Monocerotid meteor shower

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  • \$\begingroup\$ 200s is a little over 3min, a fairly standard exposure time with guided astrophotography. Otherwise you‘re not answering the OP‘s question. \$\endgroup\$
    – Grimaldi
    Commented Jan 19, 2023 at 20:19
  • \$\begingroup\$ @Grimaldi, The OP mentioned astrophotography. I think I addressed his question with a useful alternative. You should look at the EXIF data of a lot of astrophotos. With commodity digital cameras, astro exposures of 200 seconds are rare these days. Most astrophotographers strive for stacking multiple independent exposures that are just long enough to avoid streaking stars — a few seconds or less, depending on focal length. If you agree, I'd appreciate your reversing your down-vote. Thanks! \$\endgroup\$ Commented Jan 26, 2023 at 20:06

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