Hi Martin,
Some answers to your questions;
Quote:
|
I know that taking an stacking shots will increase data and image quality. However digital errors are not that random so why cant I just take less shots, Say 5 shots and keep re-naming them and stack again and again with those 5 images. Would I then not be introducing less mount error etc, or is this what is done and I have been missing this all along?
|
Unfortunately there's no such thing as a free lunch. The stacking process typically involves an algorithm that determines the 'most appropriate' value for each pixel.
There are many ways of doing that (median, mean, kappa sigma, and hybrids).
The important thing is though that the more data the algorithm has to work with, the better it can estimate the 'most appropriate' value for each pixel.
Presenting the same 5 images over and over will simply get you the same 5 results over and over. Presenting the 5 images, plus the stacked image will, depending on the chosen algorithm, yield something that isn't any different at best, and suboptimal at worst.
Here's a simple example
Let's say we're stacking 5 pixels using a median algorithm.
Let's say the values are as follows;
1 3 2 9 8
The median of these values is 3
So let's add 3 to our stack
1 3 2 9 8 3
Median is still 3
Add that again
1 3 2 9 8 3 3
Median is still 3
etc.
Do the same for mean
1 3 2 9 8
Mean is 4.6
So let's add 4.6 to our stack
1 3 2 9 8 4.6
The mean is still 4.6
Add that again
1 3 2 9 8 4.6 4.6
The mean is still 4.6
etc.
Quote:
|
Also I am not sure about comments that stacking more and more shots makes up for short exposures? If I have one single 30 sec exposure and keep adding more and more 30sec exposures I just end up with a better quality (dense, more data) 30 second shot. I have not seen that stacking keeps building on the detail gained by longer exposures. Am I missing somthing here in the settings? http://www.iceinspace.com.au/forum/..../confused2.gif
|
It's very easy to create a long exposure shot from a short exposure shot. Simply multiply the pixel brightness by whatever factor you want to lengthen your exposure by.
However, as soon as you do that, you'll also notice that the noise has been multiplied by that same factor and has become much more pronounced.
And this is where the multiple exposures come in. By stacking the multiple shorter exposures, you will have reduced the noise sufficiently to allow for multiplication of the signal without the noise getting (noticeably) worse.
Quote:
|
I have been getting some nice shots that I am happy with. No hubble shots, but as good as many I have seen on the net, and not as good also. But I just stoped last night and relised I was doing all this stuff and it was working. But then I thought I had made an involentary sound like a sheep! then the light bulb came on and hence came this Post... http://www.iceinspace.com.au/forum/..../shrugging.gif
|
There are always best practices and the well trodden paths to a quality image, however, if you're happy with your the quality of your shots, then that's great!
It's always good to keep learning though - one day you'll come across something that you can incorporate into your workflow to produce something that's even better.
Hope this helps,