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by crazygringo 529 days ago
Oh that's a real shame then. The resulting composite images are certainly artistically interesting to look at, and you can see the big-picture effects like sunrise/sunset and moon, but that explains why you can't see the gradual brightening at dawn, or degrees of darkness at night.

It seems like if you wanted to do this accurately, you'd need to lock exposure to handle a bright blue sky without blowing out -- both aperture and shutter speed. And lock white balance. The question is whether that would allow for sufficient sensitivity at night. But if you're just averaging color values across a section of sky and mainly looking for moon and moonlit clouds, I think it would, since pixel noise will get averaged out and the moon is bright.
2 comments
jupiterelastica 529 days ago
Additionally to locking the exposrue time and aperture, one could also take multiple exposures, figure out the camera's light response function and fuse multiple exposures together into a single higher dynamic range (HDR) image (see OpenCV tutorial on that or Debevec et al. 1997) Assuming you can find the camera response for the very long exposure times at night _and_ the very short during the day, one could relate them to each other and display both for accurate visual comparison.
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dekhn 529 days ago
Yeah, I agree this should be using a fixed exposure (possibly on a schedule) with locked white balance. They are using an astro camera so the sensor is very sensitive, they can get away with extremely low exposure times.
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teamonkey 529 days ago
> get away with extremely low exposure times

For night sky photography with an astro cam you’re still looking at exposure times of 20-60s at night (possibly also increasing the gain at night) and milliseconds during the day. The dynamic range is immense.

As someone who has struggled with this for my own allskycam, it’s extremly difficult to have white balance settings that perform well at all times of the cycle, especially with a camera designed to be more sensitive in the IR part of the spectrum (which will always look unrealistic). Settings that give you lovely white clouds and blue skies during the day tend to give you purple skies and green clouds at night. The quality of light is different so the white balance is different.

You can use autobalance or different white balance profiles for day and night but they each have issues.

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