calibration files master or all

[Wirral man]

Hi all im in the process of taking my calibration files darks flats etc once i have done this do i load all frames into a stacking programme or just use the masters as i have a set point cooled camera? 

[kens]

Not sure I understand what you mean. The calibration frames need to be stacked into masters. Then use the masters when stacking the lights.

If you use DSS, you create the masters by loading up all the calibration frames with the first set of lights and it creates the masters for future use.

[Wirral man]

10 minutes ago, kens said:

Not sure I understand what you mean. The calibration frames need to be stacked into masters. Then use the masters when stacking the lights.

If you use DSS, you create the masters by loading up all the calibration frames with the first set of lights and it creates the masters for future use.

sorry just read my question and it was not clear i ment to ask for every new subject you image do you have to select all the calibration files ie 50 darks 50 flats etc... or from the 1st time you stack a object you can use the masters it creates??

[kens]

One thing to watch for with DSS. If your flats and flat dark subs are all in the same folder, the master gets overwritten on each filterSo I put my flats and flat darks into a separate sub-folder for each filter.

[wimvb]

If you have a parmanent setup, you can probably reuse flats, and just use the master flat that was created the first time. But if you move or rotate your camera, the vignetting pattern and possibly dust on glass surfaces will move, and you may need to redo the flat subs. Any dust that has moved between taking light frames and flat frames, will show up in the calibrated light frames, and ulimately in the stacked image. Those blemishes are impossible to remove in post processing (at best you can hide them). If you don't have a permanent setup, be prepared to shoot new flats with every imaging session. Good flats are critical if you want to reveal weak signal in your images.

Darks from a setpoint cooled camera can be reused, but have an expiration date. Over time, pixels on your sensor will deteriorate or die, and sigma clipping will not be able to remove them completely. You'll need to take new darks. The same goes if you use a bad pixel map.

[tooth_dr]

Just to jump on here..

What setting would be best for darks and bias, when stacking to create a master library?  Average/Median/Sigma Clipping?

[carastro]

Yes, you can re-use master Darks and Bias from the same camera, but the darks need to be the same temperature and length as the lights, as stated above you can re-use flats if you haven't moved anything.  If you've moved anything you'll need to re-do them.

I have a library of darks and Bias, but I must confess I do load all the separate subs, though I know you can use a master, just force of habit I guess. 

Carole 

[wimvb]

5 hours ago, tooth_dr said:

Just to jump on here..

What setting would be best for darks and bias, when stacking to create a master library?  Average/Median/Sigma Clipping?

Average, not median. Avoid using median. As for sigma clipping; make sure you don't clip hot pixels in your darks, because you need those when calibrating light frames.

Darks need to be taken at the same settings (gain/iso, temperature, time) as the lights. Bias need to have the same gain/iso and temperature as the darks/lights, but the shortest exposure time your camera can handle. If you move your setup between sessions, flats are actually the most critical of the bunch. Moving or rotating the camera changes the position of any dust bunnies. With a mobile setup you should really shoot flats immediately after you shoot light frames. For a fixed setup you can create a flat library, and reshoot when you see that the old ones no longer work.

In short: darks and bias correct electronic issues in your light frames, so you need to take these at the same electronic (camera) settings as the light frames. Flats correct optical issues, and need to be taken at the same optical settings: same focus, camera orientation, etc.

[tooth_dr]

1 hour ago, wimvb said:

Average, not median. Avoid using median. As for sigma clipping; make sure you don't clip hot pixels in your darks, because you need those when calibrating light frames.

Darks need to be taken at the same settings (gain/iso, temperature, time) as the lights. Bias need to have the same gain/iso and temperature as the darks/lights, but the shortest exposure time your camera can handle. If you move your setup between sessions, flats are actually the most critical of the bunch. Moving or rotating the camera changes the position of any dust bunnies. With a mobile setup you should really shoot flats immediately after you shoot light frames. For a fixed setup you can create a flat library, and reshoot when you see that the old ones no longer work.

In short: darks and bias correct electronic issues in your light frames, so you need to take these at the same electronic (camera) settings as the light frames. Flats correct optical issues, and need to be taken at the same optical settings: same focus, camera orientation, etc.

Thanks for that Wim, I'm happy enough with what they are and do, I just wasnt sure which settings, as there is conflicting advice on different forums!  I've lots of darks taken at -15oC of various exposures, so I plan to get these stacked and ready for when I get a few clear nights, next week is looking good.  I had a feeling sigma clipping might not the best based on your explanation.

 

All the best

Adam.