[Shiraz (Ray)]

Originally Posted by alistairsam

Hi Ray,

Mine's an STF8300M

I do have bias frames and this is what I get

background 858.30
maximum 921

you've mentioned
SBIG quote 9.3 e read noise and 0.37 gain for their STF8300


ADU = Bias + 10*RN*RN/camera_gain

ADU = (970)860 + 865/0.37
which is 3307

Is this what I should aim for?

Your bias is ~860 from your measurements, combine that with the SBIG specs and about 3200 is what you aim for - no need for it to be exact, somewhere between 3000 and 3500 maybe.

Congratulations, you have now completed the calibration of your camera - from here on in, adjust sub exposures so that your lights have background values between about 3000 and 3500. That's all you need to do.

here are some values from my previous images


8min L - 4050

this was a reasonably good exposure for the conditions, but you could have shortened it a bit if you wanted - 5 minutes would have yielded a bit over 3000, so would have still been OK for noise, but with almost twice the dynamic range.

Do we aim at a relatively empty patch for the measurements?
above was from different nights.

Use the region that you are going to image (or somewhere close by). I presume that your capture software will allow you to put the cursor on a test image and read out the ADU - just test a few points in a blank sky region near the field centre to find a rough average value - that will do. Don't worry if it is a bit out of spec - the sky will vary in brightness through a sequence anyway, so just get exposures that are in the ballpark and err on the longer exposure side.

For NB, use "as long as possible", even your 20 minutes exposure did not get anywhere near 3000.


I might run a sequence and plot it to see the trend for the stf and my skies.

thanks
Alistair

Good luck. Ray