First light artifacts. Should I worry?

[Datalord]

Hey,

I have had first light with my CFF 12" RC, with a G3-16200, which is the usual nightmare of tinkering with all the stuff that needs to click. I got some reasonable focus on a took an hours worth of data on Sadr. Below is a stack of 4*180s blue WITHOUT flats, with and AutomaticBackgroundExtraction done in PI.

Dustbunnies, ok, flats will deal with that.

The "copycat" diffraction spike is only present in the blue. Is that a filter problem? I use Baader LRGB.

The huge odd pattern, what is that?! I don't presume flats will cure that.

 

[Merlin66]

A bright central object well over exposed.....inevitable.

 

[Datalord]

2 minutes ago, Merlin66 said:

A bright central object well over exposed.....inevitable.

 

In other words, nothing to worry about?

[Merlin66]

I would image on a better target before worrying.

 

[Zakalwe]

Its the imaging equivalent of shining a torch down the tube and worrying about dust on the lens.

[Datalord]

2 hours ago, Zakalwe said:

Its the imaging equivalent of shining a torch down the tube and worrying about dust on the lens.

Well, my assumption was that imaging on something extreme would reveal things I have to sort before trying fainter objects. 

Thanks for the comforting words. 

[vlaiv]

Out of 3 outlined squares I would just worry about middle one.

Right one is related to dust and it will be corrected with flats.

"Additional spike" is either satellite / airplane trail or another bright star out of the FOV that had it spike enter FOV. I believe it is first one, as it looks like not being fully perpendicular to spike from central star.

This is easy to check - first examine all 4 subs and see if it is present only on one - then it is satellite trail. If it is present on all four subs - look at that particular area of the sky and see if there is another bright star that would fall just outside FOV.

If it's satellite trail - sigma clip will get rid of such things (not sure if it will work on only 4 subs properly - not enough data for proper rejection).

What I would worry about is following:

That repeating pattern of unfocused light is something very strange, I can't even imagine what would cause that - it's usually down to internal reflections (filters / flatteners / etc) but that creates concentric patterns (like you would get from a single star if you superimposed different focus position on top of each other - each successive one being quite a bit less brighter - since only small percentage of light gets reflected). Such pattern is present in the image - central star and first "doughnut"/halo around it. I have no idea why this halo repeats in X and Y direction regularly. It might have something to do with sensor micro lenses - these are oriented like that.

Try to figure out what is causing this reflection and vary spacing between this component and sensor if you can. Depending on filter type you can get this with even much less bright stars, and grid repetition of it is not something you want in your images.

Here is example of it with RC8" and not as bright star:

This is from stack of subs, about 2 hours total.

Some targets will have stars of that brightness around, and you don't want repeating halo to show up on your images - so investigate that further and see if you can eliminate it.

[Datalord]

So, I asked the seller of the scope to have a look and he sent it on to CFF.

Meanwhile, today, while I was adding some stars to my pointing model, I used Vega. Placing vega in the top left, made a clear projection in the bottom right where I essentially saw the inside of the scope, with vanes and everything. So that was definitely a reflection.

Right now it is trying to tick away on some Ha and O3 on M27. I'll post a quick and dirty stack from there tomorrow.

[Datalord]

Went back and checked the individual frames. This pattern above is only present on the RGB shots, not on the luminance. So I guess it's a filter problem, but why? And how do I get RGB to work with this setup?

[Adam J]

On 29/10/2018 at 23:04, Datalord said:

Went back and checked the individual frames. This pattern above is only present on the RGB shots, not on the luminance. So I guess it's a filter problem, but why? And how do I get RGB to work with this setup?

It's a micro lense diffraction pattern for sure. I wouldn't worry, that's a very over exposed very bright star. Try the horse's head. That's a more realistic test.