I need some help with photostacking

[Jack Meehoff]

Hey y'all,

So I have some questions about photo stacking, I can't seem to figure it out. Just wondering if anyone could help to simply explain what the process is. I can only seem to find a lot of convoluted explanations.

So first I understand the dark frames you take about 20, lens cap on and with all the same settings as the light frames. And take them right after you shoot your lights.

Then Bias frames also take about 20, same settings as light and dark, lens cap on and shortest possible exposure. take them right after you shoot your lights.

Flat frames so I've heard a few things, from my understanding you use the same settings as the lights, darks and bias, but you cover the lens with a white T-shirt or something then smooth out the folds then take 20 shots but at a bright light or at the sky?

So my 2 questions are, first regarding the flat frames, what is the easiest way to do this? during the day? in the morning? what will produce the best results, and is the least complicated.

My second question is I do not understand the light frames, I heard It would be ideal to have between 20-40 light frames, but if you are taking 40 frames of the exact same scene at say 45 seconds or whatever, are you not going to get trailing when you stack all of the photos together?? or do the stacking programs correct for this?

Thanks

 

[maremarmar]

Flat frames so I've heard a few things, from my understanding you use the same settings as the lights, darks and bias, but you cover the lens with a white T-shirt or something then smooth out the folds then take 20 shots but at a bright light or at the sky?

So my 2 questions are, first regarding the flat frames, what is the easiest way to do this? during the day? in the morning? what will produce the best results, and is the least complicated.

My inexperienced advice would be just to ignore flat frames (like I do). From what I know, they are the least significant type of frames.

My second question is I do not understand the light frames, I heard It would be ideal to have between 20-40 light frames, but if you are taking 40 frames of the exact same scene at say 45 seconds or whatever, are you not going to get trailing when you stack all of the photos together?? or do the stacking programs correct for this?

Yes, the stacking programs do all the corrections (aligning, rotation). Usually, you take a single frame as long as possible (to acquire as much light as possible), but short enough to avoid trailing.

20-40 frames is good number, because "effects" of stacking are proportional to square root of number of frames (so, further increasing number of frames gives smaller effects).

You can take much more frames, however there are some limitations. For example, when using ultra-wide lenses (especially fish-eye): the sides of frames are heavily distorted while rotation, so after too many frames (that is, significant angle of rotation) the automatic aligning/rotating in DSS cannot help anymore. Of course, I'm talking about imaging without tracking.

 

[Dogglet]

For a longish while (9 months), I just shot darks & bias, until I realized that flats would do away with the obvious vignetting I was getting in some pictures. In some cases, I could crop the vignette away, in others I couldn't. In these cases, I'd always hear my friends ask "why aren't you shooting flats". Well, I do that now, and voila no more vignettes. And dust spots.

I use an EL panel @ ISO400 and shutter speeds from 1/15 to 1/60 to get the light curve near or just to the right of centre in the histogram. Very easily done. Important is not to change the optical aspect of your setup or focuser.

 

[Tristimulus]

Seems like newer cameras from about 2008 do not need dark frames (on chip magic take care of this dark side of the trade). With my Atik camera images become MORE noisy if applying dark frames. Technology move on but old traditional stay...

Roger N Clark and other nocturnal gurus have a lot sound information about astrophoto gear and methods on their web pages. They share genenously!

 

[starman1969]

I did away with any calibration frames on my last run out. Mind, my ISO was no more than 1600 and I used 800 ISO for most of my stuff.

I just didn't have time to take extra frames, but I'm sure it would have made little difference re my settings.