LRTimelapse Forum

hi,

just a quick question for shooting milky way timelapses. At constant aperture (wide open), is it better to shoot with long exposures (for example 30sec with high ISO) or stack multiple smaller exposures (for example 10sec by using multiple echos in additive mode in after effects ans maybe lower ISO also)?

The first solution will get more light and maybe more small stars (a supposition) but the 2nd will help a lot decreasing noise and you can easily choose how many echoes you want before having trails.

Maybe it's just a matter of gear. With a Canon 6D and a f/2.8 or f/1.4 wide lens, maybe noise is not a problem at high ISO but with my Canon 550D and a Samyang 8mm f/3.5, if I go beyond 800 ISO, it start to get noisy.

Here is a exemple with echo stacking (10sec exposure, interval 11sec, f/3.5, ISO 1600, stacking : echo with 4 pictures in additive blend mode with 0.8 decay, final speed x2).



It's not really a good milky way timelapse (my first test ever at shooting stars and not the better gear to do it), but it's just to add some video to the post

I've never used stacking for Time Lapse, so I can't say. I always use high ISO and up to 20 seconds exposure time. I assume this is the easier and less complicated way and normally delivers very good results. That "echo" would have to be applied after developing the RAW files, so you will be limited in your developing and loose quality in comparison to a straight, all-raw-workflow with LRTimelapse/Lightroom and single exposures.

Neat idea. You are right in that stacking decreases noise (not increasing signal) but ultimately, I'd guess its dependent on your equipment weather this is an advantage here. Do a side by side and see which result pleases you more. Shorter exposures will equal less exposure time per hour as you have to write and that's gonna add up. And yes the 6D or better yet a7s will yield several stops advantage in ISO

After testing side by side :
- 1 long exposure : 30sec, ISO 1600, f/3.5
- 3 staked shorter exposure (blend mode additive or screen) : 10sec, ISO 1600, f/3.5

The result is not the one I expected.
While the 10sec are too underexposed, you have to get the exposure right before stacking, and this add even more noise that you'll can get back stacking them.

So as Gunther said, the long exposure seems to be a better choice, less complicated way.

The only thing that seems weird is that with the 30sec, f/3.5 fixed parameters, the 800 ISO +2EV in Lightroom, 1600 ISO +1EV and 3200 ISO +0EV aren't really different in quality and noise.
What is the best choice, get the ISO as high as possible to get the exposure right out of camera ?

Because you are amplifying the noise that's all ready there. If you have not yet, read this article, I found it very informative wit regards to the sources of noise.

http://www.dpreview.com/articles/8189925...s-of-noise

Intersting article. Read it some time ago but I think I started with the second part so I didn't understand anything lol. Make much more sense reading it from the start. Still have problem completly understanding everything about upstream and downstream noise but the part on shot noise was well explained.

And regarding the small differences between the 800 ISO +2EV in Lightroom, 1600 ISO +1EV and 3200 ISO +0EV, the worst noise must be the shot noise for my camera.

I am betting that you are correct.