JimH123 wrote:
That's the beauty of stacking. It aligns each image so that all the stars line up on top of each other. And I used 4 sec only because I wanted to preserve star colors. When you expose for too long a time, all the bright stars saturate and as saturated stars, they all appear white. If I can expose for a shorter period of time, the color can still be seen. Now the advantages are stacking are that the stars become more distinct and the background appears darker due to an increase in the signal to noise ratio of the image being made up of additional images. But the big thing is that noise goes down too. For any given image, there will be noise. On the next image, there is noise too, but the random placement of the noise means that they noise specs don't line up in exactly the same pixel positions. And as you add more and more images, the image quality goes up as the noise goes down.
To do this stacking, there is a free application called 'DSS' which stands for Deep Sky Stacker. I suggest only downloading from the actual site since there is no guarantee how clean a program is coming from some other URL: http://deepskystacker.free.fr/english/download.htm.
There are a ton of settings in DSS, but the settings all have a default and for the majority of things you might do, the default settings are fine. I also like to add 'Darks' which means that I just capture some additional images with the lens cap on, but same camera settings. What it does now is to locate the stuck at pixels and DSS uses that information to fix the DSS output so that these stuck pixels don't show up in the final result.
After DSS runs, it creates a file called 'autosave.tif'. I don't do any additional adjustment within DSS and go straight to Photoshop to stretch the 'autosave.tif' file. First thing to do is to go to adjustments and change 'mode' from 32-bits to 16-bits. And then I do 'curves' and then 'levels', perhaps over and over until I get the result I want. I also use a plug-in from RC-Astro called XGradient to make the sky be a consistant dark color.
I use version 3.3.4 and find that the next earlier version doesn't support my cameras.
Some of my efforts are done with telescopes, and some with cameras and camera lenses. Just to show that I may use a longer shutter time, I am attaching the results of a stack of 15 + 10 darks using an Olympus em5ii and a 400mm f5.6 old m42 Pentax lens. This gives an effective focal length of 800mm, but is useful to see what focal length is needed to see galaxies. But some are closer and some are farther away, so you see all types. This one is 15 images of 60sec each with ISO 1600.
And just for fun, an image of Markarian's chain which shows a ton of galaxies. With the 400mm lens (effective 800mm), you can see about 15 galaxies, but a bigger scope sees far more.
Finally what can be seen using a telescope. The scope has a longer focal length, and the camera is a CCD camera (Atik Infinity), and you get image #3. This was a 40 sec image stacked 40 times.
Hope this explains a few things.
That's the beauty of stacking. It aligns each ima... (
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