July 2020 Part 2 — This Month Through Your Adapted Lens

Started 2 months ago | Discussions thread
Travis Butler
Travis Butler Senior Member • Posts: 1,393
Re: Some Astro Success

Alan WF wrote:

You say you didn't see much improvement with stacking, but how many images are you using?

Between 8 and 15. Unfortunately, the clouds were moving fast enough that I really couldn't get many more than that.

Hmm. You should see significant improvement with 8-15 images in a stack. Naively, that's like having 8-15 times longer exposures or working at an ISO that is a factor of 8-15 lower.

I have to wonder if the stacking program might have been part of the issue. If you look at the second comet photo at 100%, you can see a number of artifact trails; streaks of solid non-aliased red, blue and bright white-ish pixels.

I used Lynkeos for all of the stacking. I also tried the demo of AstroPixelProcessor and couldn't figure it out; Starry Sky Stacker apparently only works with equatorial tracking, and Starry Landscape Stacker (the program the common author recommends for stationary tripod shots) didn't do badly, but...

...I dunno, it doesn't seem *that* much better. It's missing the pixel-level artifacts, at least.

I couldn't find much on suggested settings - ISO range, exposure length, number of photos - in the time I had to research, beyond 'more photos are better!' Oh, and talking about star-tracking mounts if you're doing extended sequences. Do you have a recommended set of parameters?

Here is a suggestion for the Milky Way, but I'd expect it work for comets too:


Caveat: I've never photographed a comet.

Thanks for the reference!

Slightly out-of-focus stars often show colours better than in-focus stars. I've seen stacks of images going from in-focus to out-of-focus, without correction for sidereal motion, and each star forms a wedge. These show the colours of different brightness stars quite nicely. Perhaps something to try once you get better weather?

Definitely sounds interesting! I definitely need to get caught back up on sleep first, though.

I've had a quick Google, and can't find any examples just now.

I typically focus using waaaaaay high ISO, live view, and magnified view. I then (try to remember to) switch to a lower ISO for deeper images.

Thanks again! Comet will probably be gone by the time the skies clear around here, but will be worth trying for some sky shots. I do wish I'd done a better job focusing with the Rokinon; I've seen good reviews for it as an astro lens, and I was pleased with the clarity and colors.

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