I am a total beginner when it comes to astrophotography, so these questions will probably make you roll your eyes . Please, bear with me.
First, a little bit of context:
- At a high level, I understand the concept of image calibration and the need for darks, flats, flat darks, etc., although it's been only theoretical at this point... I learned about calibration by reading the excellent "The Deep Sky Imaging Primer" book.
- I have a ZWO ASI 533MC Pro on order. It should arrive (hopefully) before the end of the year.
Now, here are a few questions regarding calibration frames:
1) Bias frames and modern CMOS cameras:
I read somewhere that many people forego bias frames all together with these new CMOS cameras due to their extremely low read noise. Is this accurate? Or am I misunderstanding something? Not having to worry about yet another type of calibration frame would sure help to simplify the entire processing workflow!
2) Dark frames:
If I understand correctly, one of the benefits of a cooled dedicated astronomy camera over a DSLR is that because these cameras are temperature controlled, I can use them at any time of the day to take dark frames, as long as I use the same temperature, gain, offset, and exposure time for the darks as I do for the light frames (e.g, -10C, gain 100, offset 70, 30 second exposure). This is great because doing so does not take away any time that could be spent capturing the night sky. Also, if I understand correctly, one has to take a large number of these dark frames (e.g., 100) and stack them in software like PixInsight for example, and I suppose the result is called a "master dark". Assuming these statements are not completely incorrect (feel free to provide clarification if I am way off), here are a few questions:
a) How do you take these dark frames? I am familiar with N.I.N.A., but I don't see an easy way to do this with that software. I guess one could use the sequencer, but that sequencer relies on an object to be added as a sequence target. What do you use as a target object when you take darks in the middle of the day from within the house? Or do you just use a bogus object since it does not matter, and set the type of the frame to DARK? I am just guessing here... Or is there a better way to do it with N.I.N.A. or other (hopefully free) software?
b) How many dark frames does one usually stack to create a master dark? 10, 100, 1000?
c) How often do you need to recreate a master dark? Every 6 months? Once a year? More/less often?
d) I think I remember reading somewhere that it was possible to "scale" a master dark, i.e. create a master dark from 30-second dark frames, and create a version of that master dark to use with 2-minute light frames by, I guess, multiplying the value of each pixel by 4 (just a guess...) Is this correct? Can you do that in PixInsight? (Note: I don't have PixInsight, but will probably buy a license eventually since it seems to be the de-facto standard)
Again, I apologize if these are stupid questions. But any pointer would be greatly appreciated. Thank you so much!
San Jose, CA
Edited by jlecomte, 03 December 2020 - 12:55 AM.