Help processing M31!

[ZiHao]

Tried my best to pull out what I have from 2.5hours of data but it still looks very bad! Stacked in APP and edited on PS. As I neutralize the background with PS using black point dropper, all the noise popped out, and further edits with the image doesn't really help. Maybe because the flats taken are not effective enough (I was reusing the flats taken last time), I will try to take new flats to remove the new bust bunnies if possible. 

Edited September 2, 2019 by ZiHao

[bottletopburly]

Is your setup permanent? Otherwise new session new flats , did you take darks  too , 

[vlaiv]

Not sure if the issue is with flats.

Inspect your subs - you might have couple of them with high altitude clouds creating uneven background.

[ZiHao]

5 hours ago, bottletopburly said:

Is your setup permanent? Otherwise new session new flats , did you take darks  too , 

Nope, I guess I will take a new set of data some day. I am using a non-cooled DSLR, so I guess darks wouldn't help much as the temperature doesn't match?

 

3 hours ago, vlaiv said:

Not sure if the issue is with flats.

Inspect your subs - you might have couple of them with high altitude clouds creating uneven background.

Removed 70 subs with a red tint on the corner, and it helps a bit. Now the final image is surrounded by a circular red ring. Need more data next time. Attached is the final image, darkened the image to conceal the red colour in the background.

[Rush]

Can u upload a stacked image right out of APP or DSS. Not touchiing the saturation silder ?

CS

[ZiHao]

12 minutes ago, Rush said:

Can u upload a stacked image right out of APP or DSS. Not touchiing the saturation silder ?

CS

https://www.dropbox.com/s/zv6m8a9vvmon0xo/done.TIF?dl=0

[Astrobug]

It looks like the skybackground is not the same for each color. Can you remove the gradient  for each color and not at once in RGB?

 

Edited September 2, 2019 by Astrobug

[vlaiv]

I have to say that this is beyond me ... I have no clue what might be causing this - it is possible that flats are to blame.

You said that you used old flats? If you remove camera from the scope or change focus or anything - old flats are not going to work. Also need to do proper calibration - which includes darks or at least bias.

I tried fixing things, and there is simply no way to fix the above. Concentric rings look like some sort of issue with vignetting - possibly due to use of old flats and wrong calibration.

Interestingly enough green channel does not have this issue - only red (I did not check the blue one).

[Rush]

9 hours ago, ZiHao said:

https://www.dropbox.com/s/zv6m8a9vvmon0xo/done.TIF?dl=0

 

👌 K.

[Rush]

This is what remains after cleaning up.

RGB channels

R

G

B

CS

 

[ZiHao]

On 03/09/2019 at 04:19, vlaiv said:

I have to say that this is beyond me ... I have no clue what might be causing this - it is possible that flats are to blame.

You said that you used old flats? If you remove camera from the scope or change focus or anything - old flats are not going to work. Also need to do proper calibration - which includes darks or at least bias.

I tried fixing things, and there is simply no way to fix the above. Concentric rings look like some sort of issue with vignetting - possibly due to use of old flats and wrong calibration.

Interestingly enough green channel does not have this issue - only red (I did not check the blue one).

Thanks for helping anyway! It is calibrated with 100bias and 15 flats, old flats which might be the problem here. I have 4 hours of dumbbell nebula with me now so I will try to stack them with and without flats.

[wimvb]

@vlaiv is right on the money. You used flats that didn't properly calibrate the lights. This causes weird vignetting and leaves dust bunnies. You also have walking noise, the noisy streaks in the background. These can be reduced by using cosmetic correction and playing with the kappa rejection settings. The only sure way to remove this pattern is by dithering; move the mount in a random direction some 12 - 15 pixels between exposures.

The bortle 8 sky doesn't help either; it causes gradients and a lot of noise. Once you remove the light pollution by adjusting the background, you're left with the light pollution noise. If you image from a site with light pollution, you need to increase the total integration time. For each hour of integration time from a magnitude 20 site, you need 2.5 hrs from a mag 19 site, 6.25 hrs from a mag 18 site, etc.

I downloaded your master file, and to me it seems underexposed. I would expect to see more stars in the unstretched image. What was your single sub exposure time? Did you use a light pollution filter?

Edited September 6, 2019 by wimvb

[ZiHao]

16 hours ago, wimvb said:

@vlaiv is right on the money. You used flats that didn't properly calibrate the lights. This causes weird vignetting and leaves dust bunnies. You also have walking noise, the noisy streaks in the background. These can be reduced by using cosmetic correction and playing with the kappa rejection settings. The only sure way to remove this pattern is by dithering; move the mount in a random direction some 12 - 15 pixels between exposures.

The bortle 8 sky doesn't help either; it causes gradients and a lot of noise. Once you remove the light pollution by adjusting the background, you're left with the light pollution noise. If you image from a site with light pollution, you need to increase the total integration time. For each hour of integration time from a magnitude 20 site, you need 2.5 hrs from a mag 19 site, 6.25 hrs from a mag 18 site, etc.

I downloaded your master file, and to me it seems underexposed. I would expect to see more stars in the unstretched image. What was your single sub exposure time? Did you use a light pollution filter?

I first did a polar alignment on PHD2 using my guiding rig and everytime after polar alignment, I wouldn't even try guiding on an EQ3 pro and instead went for the 30seconds maximum exposure sidereal rate tracking. Next time I'll try the settings on DSS to eliminate the walking noise and of course don't be lazy to take flats...

Single sub exposure time is 30 seconds only and no light pollution filter was used. Gonna save up for HEQ5 and that will probably help a lot compared to my bare minium setup right now. Thanks for your help.