lens/stacking or light polution artifact ?

[Run45]

Hi,

This is just my 2nd astrophotography attempt. I was talking pictures of the nightsky from my light-polluted london garden just with a D100 and the StarAdventurer.

I just tried to get Andromeda galaxy in the shot to play later with post processing : using DeppSpaceStacker and Photoshop.

Actually I am quite happy with the result given the circumstances (=London, just a standard D100 with standard wide angle lens) .

Probably I "overcooked" the image in Photoshop a lot but personally I am quite happy with them. I attached 2 post-processing attempts of mine.

Now the thing I wanted to ask is the following: To get the galaxy to show in the image I added quite a lot (=6) of curves in Photoshop using the method described

in http://www.budgetastro.net/photoshop-basics.html .

It all works great but I get a spherical(circular?) background glow in the background image.

Any idea what this is ? Given that its dead-center of the image I  assumed its somehow connected with the camera lens. (I guess light polution would be not that symmetrical ).. Or is that and

artifact of the stacking process ? Is there a way to work around this artifact ? Maybe I should have just centered Andromeda in my image in the first place .. maybe next time....

I attach the fulll un-cropped  image that shows the artifact I am talking about (Processing done at that stage : convert 32bit to 16, adjust levels, add 6 curves to get galaxy showing)

Thanx for any advice.

[happy-kat]

Possible lens vienyeting. If it is flats would take care of that.

[Victor Boesen]

Did you take any flats/bias/darks? Because flats should have been able to remove some of the vignetting.

[Knight of Clear Skies]

Andromeda is standing out nicely there. The circular glow is vignetting caused by the lens. It's normal for lens and telescopes to produce a darker corners but in this particular case it's exaggerated by the amount of light pollution in your vicinity. From a dark site it's much less noticeable. Taking and stacking with flats should sort it out, or it can be removed in post-processing with Gradient Xterminator or something similar.

[lux eterna]

Hi Run45,

It looks to me your lens is suffering from vignetting. Wide angel lenses often do, specially when the aperture is full open. Stop down can help, but you will obviously need longer exposures then. Another option is to get the PS plugin called GradientXterminator.

Ragnar

[Victor Boesen]

Tried to fix it in lightroom (curves, radial filter etc). I think it turned out pretty good. I was able to pull out m33 as well as a little smudge (follow the three stars from m31 up the image and you should come across it) Tell me what you think.

(looks like you have a little smudge on your lens in the bottom right corner, but nothing too worrying)

[Run45]

that look good thanx will give this a go myself.

Thanx for all the comments. I only had darks and lights .. no flats/bias taken... good to know what it is now so I can try to do better next time ...

Thanx so much for all the comments and advice (will give gradientXterminator a go as well)

 

[Victor Boesen]

3 minutes ago, Run45 said:

that look good thanx will give this a go myself.

Thanx for all the comments. I only had darks and lights .. no flats/bias taken... good to know what it is now so I can try to do better next time ...

Thanx so much for all the comments and advice ...

You are welcome! Feel free to ask again next time you need help!!

[happy-kat]

Taking flats will in general be good for improving images and deal with lens smudge dust bunnies.

[Run45]

tried gradientXterminator .. looks good to me ... think I am happy with that ... need to take flats next time

[Knight of Clear Skies]

That's come out well. You've also picked up M33 as mentioned above, the Double Cluster at top right and another large cluster towards the top left.

[Run45]

That makes me happy .. never managed to see M33 from my light poluted garden with the telescope .. very happy to have got it just with my 100D+stock lens

 

[Victor Boesen]

33 minutes ago, Run45 said:

 

tried gradientXterminator

 

I need to buy it when i get into serious astrophotography. 

[Stub Mandrel]

Gradient Exterminator Is Your Friend :-)

[Run45]

So glad I posted this. Completely missed m33 , double cluster etc.. I was so focused on m31 that I forgot everything else... now found even E.T/owl cluster... very happy with the result . Thanx again everyone.. 

[Stub Mandrel]

A great reminder of how much you can get out of a widefield shot.