Master Flat tutorial question

[topboxman]

From PixInsight Master Calibration Frames tutorial at:

http://www.pixinsight.com/tutorials/master-frames/en.html

In the Master Flat Generation (I) section, it checked "Calibration" boxes for both Master Bias and Master Dark. Is this correct? Wouldn't it perform double Bias subtraction and introduce more noise? Should the "Calibration" box be unchecked for Master Bias and checked for Master Dark. I believe checking "Optimize" box is correct under Master Dark section to have Master Dark, Bias-scaled to the Flat.

If the tutorial is correct, please explain how the "Calibrate" box works.

Thanks,
Peter

[pfile]

if your masters have not been bias subtracted, then the bias signal is present there. in that case you need to tick "calibrate" under the master dark and master flat areas of IC while calibrating your lights.

if the dark subs were bias subtracted before integrating, then you leave "calibrate" unchecked while calibrating your lights. similarly if the flat subs were bias subtracted or had flat darks subtracted, then leave "calibrate" unchecked while calibrating lights.

double bias subtraction would only happen if you pre-subtracted your masters and also ticked 'calibrate'.

i always precalibrate my dark and flat subs, then load a master bias, so i never check "calibrate"

rob

[topboxman]

Hi pfile,

Thanks for making a very clear statement.

Peter

[topboxman]

In the case of Master Flat Calibration to calibrate individual flat subs. What does it do when both Master Bias and Master Dark have "Calibrate" boxes checked as shown in PixInsight tutorial? Isn't that a double bias calibration (or subtraction)? This assumes Master Dark has not been previously Bias calibrated (or subtracted).

According to the hints for "Calibrate" box, both says

"Select this option to calibrate the master bias (or dark) frame at the beginning of batch calibration process".

If both "Calibrate" boxes are checked, won't it result as double bias subtraction or is PixInsight smart enough to prevent this?

Please see the following link and look under Master Flat Generation (I) section where it shows both Master Bias and Master Dark "Calibrate" boxes checked.

http://www.pixinsight.com/tutorials/master-frames/en.html

Thanks,
Peter

[pfile]

well, i think that's something different. that's telling IC to do additional work to the master bias - to apply any defined overscan regions to the master bias.

http://www.mirametrics.com/tech_note_overscan_bias.htm

if you hover over the "calibrate" checkbox for the master bias it alludes to this.

so, that's probably checked because vicent is using some research-grade equipment which has overscan regions...

rob