Hi there,
I've tried two methods of measuring my ASI1600's individual performance and can't get either to work.
I've tried following
Craig Stark's tutorial, and the
BasicCCDproperties Script in Pixinsight.
The PI script fails to execute, citing an error regarding the variable 'this.x0'. Some have suggested simply removing the variable from that line. I've tried that too, to no avail.
Doing it manually via Craig Stark's tutorial, I get stuck at the flats section.
So, I have to take pairs of flats where the only thing that changes is the number of photons hitting the sensor. Rodger that.
But the numbers are killing me here.
From what I can tell, I take one flat (presumably the brighter one) and read the mean value, say 38629. Then I multiply by 2 to get 77,258 (why? I don't know and he doesn't say)
Then I make a difference image with a 5000 pedestal value added to the first image to make sure everything comes out in positive numbers and no data is clipped. I don't have ImageJ, whatever that is, so I try pixelMath in PixInsight. I edit the expression to read "(image2+5000)-image 1"
At this point, every single pixel is maxed out to white. If I change the pedestal value to anything other than 0 or 1, it maxes out.
At this point I'm stuck because the tutorial is good on what to do, but not so good on why, so it's hard to extrapolate a solution when things go awry.
I can read off the values in PI statistics but is avgDev or MAD the same as a Standard Deviation?
I don't mind getting my hands dirty in a spreadsheet, but I don't really understand what he's doing. Surely the pedestal value thing means all your data will be wrong by 5000 if you don't subtract it out later on, which puts you in the same situation of clipping? If you need positive numbers, and neither flat frame has priority here, you can simply subtract the smaller value from the greater value with no need for a pedestal. And why does it have to be mean *2?
If someone could just tell me "take these values from PI statistics and do this with them in a spreadsheet" I'd be so grateful.
I also notice there is a difference in methodology between the script and the tutorial in that the script wants two flats that are taken under the same conditions, whereas the tutorial wants sets of two flats taken at the same settings with only the light level increasing between sets.
Any help gratefully received.
Best
Markus