Astrophotography

06 Apr 2020 13:24

Hey!

I am trying to work in M81 - M82 using my Skywatcher Blackdiamond 150/750 telescope, and my Canon T5 camera. I got about 4 hours of data, and I stacked it ussing DSS with default recommended settings.

Total of 4 sessions divided in 4 groups:

Main group: 90x90s (800 ISO) lights, 20 darks, 20 flats, 20 dark flats, 1 master offset
Group 2: 44x60s (800 ISO) lights, 20 darks, 20 flats, 20 dark flats
Group 3: 6x60s (800 ISO) lights, 10 darks, 10 flats, 10 dark flats
Group 4: 44x90s (800 ISO) ligths, 20 darks, 20 flats, 20 dark flats

Then, I started post-processing with Pixinsight, but I am not happy with the result. There is A LOT of noise (mostly blue) that I cannot get rid of.

I don't know if any of you experts can see anything that is clearly wrong with it. I would really appreciate if you could give me some advices, because I am truthly frustrated. It could be equipment, technique, stacking, processing...

EDIT: I am retrying rotating so the bands are vertical, and without using the ColorCalibration process and instead of a blueish/purple noise, I get some sort of multicolor noise:

vlad01 · 07 Apr 2020 01:03

I would do all the stacking and processing in pixinsight and forget DSS, you will get better results as it's a much better program with better capability. You can also use dithering in pixinsight which will help get rid of the noise.

Could also be a limitation of the camera. We use a EOS 200D and it's not that great, lots of noise as well.

07 Apr 2020 02:35

I've never heard before of dithering, and while looking for a solution for this noise issue, I find it everywhere. I was think about doing it for my next set if pictures.

I didn't know there was a dithering option in Pixinsight. I guess I can try using it for stacking too, but I always though that DSS was better for this.

Thanks you vlad01!

vlad01 · 07 Apr 2020 02:55

No probs, It's actually my friend who tried pixinsight and found it much better than DSS. I personally use DSS for ease of use and to preview the results and my friend then does the proper pic in pixinsight as he knows how to use it, I haven't used it as of yet but he showed me all the things it could do that DSS was lacking in, dithering was one of them.

He uses backyardESO for the capturing and it supports dithering. He uses it in conjunction with PHD for the guide scope.

A-L-E-X · 08 Apr 2020 18:09

I have a question about avoiding star streaking in untracked tripod astrophotography. Is the 400 rule a good one to use regardless of sensor size? 400/shutter speed..... I have found it works well with my 16 MP M4/3 sensors, would it also work well for smaller sensors (like superzoom 1/2.3" sensors?) So if you were using a 800mm EFL then the slowest shutter speed to use would be 1/2 sec and then do a lot of stacking (for example, on the Orion Nebula.)

Cantra · 08 Apr 2020 22:30

Tonight was a relatively clear night. Last night it poured rain so I was unable to see the supermoon, but tonight I was able to get some good pics.

Best picture of Venus I've ever taken.

Mizar and Alcor.

A-L-E-X · 10 Apr 2020 13:57

what kind of camera and lens did you use and what settings?

Cantra · 21 Apr 2020 14:40

what kind of camera and lens did you use and what settings?

For me? I just hold a phone camera up to the eye piece. I was using a Meade 130 Polaris telescope.
Last night I used the Celestron 114 lcm, it picks up more background stars and is overall a better telescope to use despite the Meade 130 being larger. The problem that I have with both of them is that the vibrations are rather extreme.
Mizar and Alcor through the Celestron 114 lcm telescope.

A-L-E-X · 22 Apr 2020 11:49

Thats impressive for a phone camera, you should considering getting one of those inexpensive phone holders that will steady your images.

Cantra · 22 Apr 2020 13:32

Thats impressive for a phone camera, you should considering getting one of those inexpensive phone holders that will steady your images.

I had one at some point, though I think I lost it. But your right, I should get one.

26 Apr 2020 14:48

Hi!

I am here again asking for your astro-help...

As I mentioned in previous posts, I have been trying to get some nice shots of M81 and M82. I had some noise issues solved with dithering, but now I see that I also have a collimation problem with my Skywatcher Blackdiamond 150/750.

Today I decided to try to fix it, but I am not sure if what I have now is good enough, of if I should keep trying to make it better (it's been hours without too much progress). I am using a collimation cap, but I have no collimation laser.

► Show Spoiler

Even if I think that the secondary mirror is perfectly in the center of the eye tube, and the donut of the primary mirror is in the center of the secondary mirror's spider vanes, I noticed that the reflexion of the primary mirror is not in the center of the secondary mirror. And actually, the shape of the secondary mirror is not 100% a circle.

What do you think? Is it actually ok? Or what should I do from this point?

Thank you in advance!

vlad01 · 26 Apr 2020 19:33

I would get a laser collimater, took me less than 5 min to correct the scope. Well worth the money.

27 Apr 2020 02:47

Already bought the collimation laser, but with the quarentine it won't arrive for another month at least. And I won't be back where my telescope is until August.

27 Apr 2020 11:11

pzampella, in Newtonian scope the secondary mirror in ellipticel in projection, and not centered. If you look carfully at the optical scheme picture, you will see that paths of edge rays are asymmetrical, thus secondary mirror must be off-center to prevent vignetting.

A-L-E-X · 27 Apr 2020 16:16

whats the slowest shutter speed one can use on the moon at 2000mm EFL? I am looking to capture some full frame total lunar eclipse images and I know totality requires rather long shutter speeds, but that at 2000mm EFL the shutter speeds need to be rather short to avoid blurring.

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