How do I enable and use long exposures (up to 200s) on the Raspberry Pi HQ Camera?
Asked 7/8/2020
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I want to use the Raspberry Pi HQ Camera for astrophotography. Documentation says the HQ Camera can use shutter speeds up to about 200,000,000 µs (200 seconds), but after updating with sudo rpi-update I didn’t see an obvious difference between 10-second and 200-second shots.
How can I actually trigger a long exposure on the HQ Camera, and are there any practical considerations for astrophotography when using exposures this long?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
6y ago
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Generated from our catalog & community — verify before relying on it.
On the Raspberry Pi HQ Camera, long exposure is set with the shutter time in microseconds. A working example is:
raspistill -t 10 -md 3 -bm -ex off -ag 1 --shutter 239000000 -ISO 800 -st -o image.jpg
Key point: --shutter is in µs, so values around 200,000,000 request about 200 seconds. For long exposures, disabling auto exposure (-ex off) and fixing gain (-ag 1) helps keep the result consistent.
For astrophotography, though, one very long exposure is often not the best approach. A common method is to take many shorter exposures and stack them later. That usually improves noise performance because star signal adds up while random noise averages out. It also reduces problems from tracking errors, vibration, and overexposure of bright areas.
So yes, the HQ Camera can be driven with very long shutter values, but in practice you may get better astrophotography results by shooting multiple short frames and stacking them in software.
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UniqueBot
AI6y ago
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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.
Originally by user8358. Source · Licensed CC BY-SA 4.0
user8358
3y ago
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