Stacking, potential silly question

Ok, so the goal is to take a number of photos of the same view and stack them. Why not just take one photo and make "X" number of copies and then stack?

the jimmy wrote in post #13349946
Ok, so the goal is to take a number of photos of the same view and stack them. Why not just take one photo and make "X" number of copies and then stack?

No silly questions, I'm curious of other's answers since I'm relatively a newbie as well. But my take..

The goal of stacking is to improve the signal by averaging out the random noise present from sub to sub. This helps bring out more of the object in post process without also increasing noise.

If you stack the same picture x number of times, you end up with the original because the noise is in the same location each time...the data is the same.

That is basically correct. Stacking the same image doesn't achieve anything!

I also have a newb question about stacking. From reading these threads people seem to use two different programs for stacking.
DSS for bringing out lots of details / stars and another type of program for creating star trail pics.

My question is if you take lets say 40 pics, can those be used both for the nice clean crisp photos in DSS and for creating star trail photos?

trossite wrote in post #13393416
I also have a newb question about stacking. From reading these threads people seem to use two different programs for stacking.
DSS for bringing out lots of details / stars and another type of program for creating star trail pics.

My question is if you take lets say 40 pics, can those be used both for the nice clean crisp photos in DSS and for creating star trail photos?

This may be possible depending on the duration of the overall exposure but generally no. Images usually taken of constellation, dso, etc normally are tracking the stars and for this reason the foreground are usually excluded.

For star trails, you want to include some foreground to make your image interesting and the image is not tracked so that you can create the star trails. Image taken for star trail though can also be use for time lapse photography which you might also want to experiment.

I believe that stacking also reduces sensor noise by analyzing all the shots and averaging them to reduce noise.

Been constantly reading through the Astronomy and Celestial thread here and in the sharing section ever since i first looked about 4 weeks ago, I can't get enough.

Just dying to get out there and try some shots, but waiting on a tripod purchase, time, and dark skys.
I'm going to Hilton Head Island over the holidays and hoping to find a nice light house to shoot with star trails.
I ordered a cable release / timer so i can set the camera up to take a number of shots timed without having to touch the camera.

My theory is to setup
set the camera to mirror lockup
use my kit lens at 18mm & f/3.5
ISO 800 or 1600
and shoot a number of shots each at an exposure of 20 - 30sec long.

Any tips or suggestions with my theory? Two things I'm worried about, not having clear skys when i get down there, but also it can be pretty windy on the island. I'm hoping that it won't be too bad and not cause the camera to shake on the tripod.

If you're really desperate, you could try just laying your camera on its back and shooting that way. Anything that makes sure the camera is stable and gets the part of the sky you want to see is good enough. BTW, 30 sec will likely be too long for 18mm, so be ready to experiment and shorten your exposures if you get trailing (unless you want star trails, of course).

I think i really want to try some star trails pics using a star trails stacking program. Is there a recomended exposure length for doing that?

As long as you can get without making the sky too bright in the resulting exposure. You'll have to experiment to find that.

cyberon wrote in post #13394658
This may be possible depending on the duration of the overall exposure but generally no. Images usually taken of constellation, dso, etc normally are tracking the stars and for this reason the foreground are usually excluded.

For star trails, you want to include some foreground to make your image interesting and the image is not tracked so that you can create the star trails. Image taken for star trail though can also be use for time lapse photography which you might also want to experiment.

Actually yes you can use DSS to stack pictures taken with fixed tripod.

I've done it here to capture M31 with my T1i @ 50mm/f1.4 via DSS
Here are 367 light frames 2.5 sec exposure each (15min 57sec total exposure), ISO800, 50mm prime @ f1.4; + 54 dark frames + 30 Bias frames. DSS processed, output into Apple Aperture 3
https://photography-on-the.net …p?p=11043548#po​st11043548

the jimmy wrote in post #13349946
Ok, so the goal is to take a number of photos of the same view and stack them. Why not just take one photo and make "X" number of copies and then stack?

The, "Signal" (real light) in each photograph (sub-exposure or sub) will be the same. The, "Noise" in each sub will be different. Stacking images improves the signal to noise ratio.

A stacking program aligns each sub based on the real light like the stars, building the signal with each additional sub. The noise is never in the same place, (or at least not constant) so it gets subdued with each additional sub.

You can also take, "Darks" of the same shutter duration with the lens cap on and stack these with the, "Lights" or subs.
Darks will recognise the false light (noise) in each sub and remove it.