PixInsight versus AstroArt for Preprocessing

[rodmichael]

"Before putting time into making many Dark frames, bear in mind that most artifacts, except for hot pixels, are contained in the bias [frames].  Consider Master Bias subtraction and the averaged subtraction of a defect map in lieu of Darks."

This makes a lot of sense to me and it is what prompts my question in a user forum where I see little mention of this methodology.  BTW, AA also offers capability to deal with column and row defects.

I'm not too sure I agree with Warrens statement on a global basis. Having done quite a lot of testing, My KAF8300 chip builds significant dark signal over my 'normal' imaging times. I have another Kodak chipped camera that shows similar results. Both are significantly 'cleaner' at -20c compared with -10c. I do mostly Narrowband imaging so sub-exposures of 20 or 30 minutes are not uncommon. Whats more that dark signal is not even across the chip from top to bottom or around the edges and that 'gradient' becomes more pronounced with time. Bias subtraction will do nothing to deal with this. Sure you could try and deal with this later on with DBE or the like but I am of the mind it is better to deal with unwanted 'stuff' at source.

... A lot of my target objects are on the faint to very faint end of the spectrum. A robust calibration workflow is essential to having any hope at all of teasing what little signal there is above background levels. Bright objects are a lot more forgiving of workflow.

I suspect many of us do things slightly differently and one of the beauties of PI is that is flexible enough to allow for these subtle variations.

Thank you for those observations.  Since exposure times for the RASA are said to be a small fraction of "normal" exposure times, I wonder how that might mitigate build-up of dark signal on the KAF8300 that you have observed.

I guess that prudence dictates at least experimentation with and/or comparison of different preprocessing workflows to be as sure as possible of what works best for my particular setup.

[Duncan]

The RASA is certainly a very fast scope at f/2.2, so you're going to collect a lot of photons in a relatively short exposure. Nonetheless, if it was me, I'd still be capturing darks, and using the fast optics to go deeper with some long exposures.

Up to you what approach you want to take; there are different philosophies here and no one is necessarily "right". But since you have the camera, and are waiting on a concrete pour for your scope pier (if I'm remembering that right) it would make sense to capture a set or two of bias and dark frames with the camera indoors in the meantime. It would also give you some practice with the camera control interface that you're using.

Even if you don't end up using the darks, it would be good to have a set archived with whatever light frames you take over the next few months. You might decide later to come back and reprocess, and it's always good practice to have a set of corresponding calibration frames in your archive with the lights just in case...

[akulapanam]

As a long time user of hyperstar I can tell you are still going to need longish exposures (2-3 minutes for LRGB and 5 minutes with a 12 HA filter) with the RASA if you want to go for dim objects like those in the sharpless catalog.  F-ratio is always assumed to mean more speed, and it does, but not quite in away people normally think about it.  Etendue, think about this as how much light is spread out over the pixels in the chip, is what really matters here.  The easy way to think about this situation is to consider resolution in arc seconds.  A RASA will be no faster than any other 11" scope at the same arc second resolution and it will always be faster than any scope of less aperture at the same resolution. Consider you could use a RASA at .83" resolution with a Sony 178/183 based chip and 2.4um pixels or you could use a Kodak chip on a C11HD with much larger 11um pixels at .83" and get the exact same speed provided QE is the same. 

The formula for comparison is aperture in mm^2 * arc sec resolution^2 * QE

[rodmichael]

As a long time user of hyperstar I can tell you are still going to need longish exposures (2-3 minutes for LRGB and 5 minutes with a 12 HA filter) with the RASA if you want to go for dim objects like those in the sharpless catalog.  F-ratio is always assumed to mean more speed, and it does, but not quite in away people normally think about it.  Etendue, think about this as how much light is spread out over the pixels in the chip, is what really matters here.  The easy way to think about this situation is to consider resolution in arc seconds.  A RASA will be no faster than any other 11" scope at the same arc second resolution and it will always be faster than any scope of less aperture at the same resolution. Consider you could use a RASA at .83" resolution with a Sony 178/183 based chip and 2.4um pixels or you could use a Kodak chip on a C11HD with much larger 11um pixels at .83" and get the exact same speed provided QE is the same. 

The formula for comparison is aperture in mm^2 * arc sec resolution^2 * QE

I will have to think about this one.  I'm struggling to grasp the concept.  Thanks.