Quote:
Originally Posted by Heian
Nice one Al,
this seem a silly question, but why do you have to take a 20sec exposure on such a bright star? I'm assuming it's software settings 
I know with my dsi3 + 120mm refractor exposure times for me are in the order of 1 sec, or shorter.
cheers
Mark |
Just trying to come to grips with exposures on the ST8, Mark. I've been trying to maximise S/N ratio, and trying to get a handle on what is the right level of exposure. The histogram when capturing in CCDSoft doesn't appear to be linear
... and the maximum value achieved is well short of what I expect.
The 20s exposure peaked at about 27000 after I subtracted the background, but the spectrum was the right shape, longer exposures were clearly clipped (at 32k intensity) - the spectrum had a flat top.
At this stage I don't think I can use the histogram to judge my exposures like I'm used to with the DMK.
I have to admit not having my head properly around what's happening with the histogram yet...
I've attached some raw spectra: 5s, 20s and 60s. The 5s spectra shows the noise, the 20s one has less noise, but the 60s one is a different shape due to clipping or the non-linearity of the ABG chip (unfortunately my ST8 is ABG
).
Al.