I just ran a sensor analysis on my OSC in RAW16 and RAW8 modes and was astonished by the difference.
Read noise was massively higher at lower gains in RAW8 mode than in RAW16 (though similar at higher gains) and e/ADU was hundreds of times higher in RAW8 than RAW16. I assume e/ADU is a measure of sensitivity of the sensor?
So why would anyone want to use RAW8 mode? Or am I missing something?
Interpreting sensor analysis data
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Re: Interpreting sensor analysis data
Hi,
8 bit mode is useful at high gains because (as you noted) the figures are similar in terms of read noise, and you typically get twice the frame rate (or thereabouts). That fits very well with typical camera use for planetary/solar/lunar, where short exposures to freeze the seeing and high frame rates are critical.
If you have a camera that can run (say) 14 bit images, then the 8 bit images are effectively made by dividing 14 bit data by a factor of 64 on the camera. That means that all the e/ADU values will be 64 times larger. Changes to read noise values are more subtle - for low gain where the 8 bit e/ADU is very large gets a very high read noise due to the fact that when you change from 14 to 8 bit you throw away any fractional parts of the new 8 bit value. For higher gains the read noise can be similar to the high bit depth read noise.
cheers,
Robin
8 bit mode is useful at high gains because (as you noted) the figures are similar in terms of read noise, and you typically get twice the frame rate (or thereabouts). That fits very well with typical camera use for planetary/solar/lunar, where short exposures to freeze the seeing and high frame rates are critical.
If you have a camera that can run (say) 14 bit images, then the 8 bit images are effectively made by dividing 14 bit data by a factor of 64 on the camera. That means that all the e/ADU values will be 64 times larger. Changes to read noise values are more subtle - for low gain where the 8 bit e/ADU is very large gets a very high read noise due to the fact that when you change from 14 to 8 bit you throw away any fractional parts of the new 8 bit value. For higher gains the read noise can be similar to the high bit depth read noise.
cheers,
Robin