Bit of advice please.

[alan potts]

This is 3 hours of 4 minute subs on M33, you know this.  I am getting a darker area to the left hand side most of the time no matter what I shoot. I tend to collect 10-15 subs per night on a target and move on, this is from a few nights and some of the subs will have been taken when the the camera was in or could have been in a slightly different position as I took it off to clean the bunnies out. Is this causing the issue or something else, I have checked the camera is not at an angle and though not perfect stars are pretty round, misshape caused by lower down guiding. I have not spent much time processing so I know it can be better.

 

Is this just a gradient of a different nature, if so I must get some software soon.

Alan

[carastro]

I would say this is simply a sky gradient and can be removed by using gradient exterminator a Photoshopp plugin, or if you use Pixinsight I think there is an equivalent process.

Caro,e 

[PeterCPC]

...or Astroflat Pro.

Peter

[Laurin Dave]

Yep looks like a sky gradient..  very minor though (he says jealously).. Here it is after a quick gradient removal (Dynamic Background Extraction DBE)  in PI..

Dave

 

 

 

 

[alan potts]

Thanks all of you I did wonder, some images don't have it but are in different areas of the sky. The problem only seems to be visible after 3-4 stretches, I have even check image both sides with the appropriate tool and can't see anything in the data but after a couple more stretches is comes out, I have manage to hide it a fair bit in most images. I thought iI was doing something wrong, I think after I come out of hospital i will get something like, Astro Flat which Steve uses, and there isn't much wrong with his images.

Alan 

[alan potts]

13 minutes ago, Laurin Dave said:

Yep looks like a sky gradient..  very minor though (he says jealously).. Here it is after a quick gradient removal (Dynamic Background Extraction DBE)  in PI..

Dave

 

 

 

 

I am assuming PI is Pixs insight, where do you buy this if I wanted it, I see FLO only have Astro Art, looks half decent now you have done that, I feel it could stretch more than I have done.

Alan

[Physopto]

https://pixinsight.com/trial/

[Laurin Dave]

Yes that was Pixinsight Alan...  just search Pleiades Astrophoto Pixinsight and it'll pop up..  not a particularly intuitive piece of software though

Dave

[carastro]

What do you normally use for processing Alan?  

If you use Photoshop Gradient Exterminator is a plugin which is not free, but a lot cheaper than buying Pixinsight.  Also Pixinsight is not exactly user intuitive.

I get gradients all the time and use GE in most images.  I think it depends on the Moon, and whether there is any distant or local LP which may not be obvious to you when imaging.  

Carole   

Edited October 25, 2019 by carastro

[Davey-T]

If you have P'Shop there's a YT video by Doug German showing a gradient removal process which works with a bit of experimenting particularly on galaxies in a no t too dense starfield.

Davde

[alan potts]

3 hours ago, carastro said:

What do you normally use for processing Alan?  

If you use Photoshop Gradient Exterminator is a plugin which is not free, but a lot cheaper than buying Pixinsight.  Also Pixinsight is not exactly user intuitive.

I get gradients all the time and use GE in most images.  I think it depends on the Moon, and whether there is any distant or local LP which may not be obvious to you when imaging.  

Carole   

I use PS CC and have no plug-ins. Astro Flat I have been told is good too. I don't really have any LP Carole apart from to the SE with could affect this shot. I see nothing in the image at all until about the 4th stretch. I have even use tools in PS to measure each side and the differences is 1-2 in RGB using PS and this I would have thought was normal but after this 4th or 5th stretch the differences can be 20 and I just struggle to see this is SKY over just over 1.4 degrees from side to side, it is not the Moon that I am sure of.

I have just done this stretch and level adjust 4 times, cropped edges out to start, now you see it clearer. The 1-3 stretch saw nothing, it looked flat.

 

Alan

[alan potts]

2 hours ago, Davey-T said:

If you have P'Shop there's a YT video by Doug German showing a gradient removal process which works with a bit of experimenting particularly on galaxies in a no t too dense starfield.

Davde

I know this technique well but it is no good on say the Sole Neb, I have used it many times on Globs and clusters, not tried Galaxies though.

Alan

[Davey-T]

3 minutes ago, alan potts said:

I know this technique well but it is no good on say the Sole Neb, I have used it many times on Globs and clusters, not tried Galaxies though.

Alan

Doesn't work on big nebulae or dense star fields, should work on your M33 ok.

Dave

[alan potts]

I wonder if it is worth trying another (7th set) of Flats and Dark Flats?

Alan

[Davey-T]

Have you compared it to other M33 images ? there may actually be a difference in sky brightness, some of that IFN stuff they talk about, never managed to capture any from S London though 😂

Dave

[vlaiv]

9 minutes ago, Davey-T said:

Have you compared it to other M33 images ? there may actually be a difference in sky brightness, some of that IFN stuff they talk about, never managed to capture any from S London though 😂

Dave

Too red and too linear to be IFN - classical LP gradient

[carastro]

I just ran your image through Gradient Exterminator and there is definitely a gradient there.

BEFORE

 

AFTER Gradient Exterminator

 

Getting rid of the gradient allows you to further stretch your image. 

This is a further stretch and an increase in the colour.

 

 

You've got some nice data there by the way.

Carole 

Edited October 25, 2019 by carastro

[steppenwolf]

This background does have quite a gradient to it and this is simply caused by light pollution. I use PhotoShop for most of my image processing and when I get a gradient like this, I use a plug-in called AstroFlat Pro which was written by Noel Carboni to correct it. I have applied this plug-in to your image and this is the result with a slight tweak to levels:-

[Davey-T]

It's amazing what the camera can pick up in a sky that looks dark to the eye, just as well really as we'd be stuffed for imaging 😂

Dave

[alan potts]

Well thank

38 minutes ago, carastro said:

I just ran your image through Gradient Exterminator and there is definitely a gradient there.

BEFORE

 

AFTER Gradient Exterminator

 

Getting rid of the gradient allows you to further stretch your image. 

This is a further stretch and an increase in the colour.

 

 

You've got some nice data there by the way.

Carole 

Thank-you Carole, this I guess is the only part of my sky where there is a touch of LP, believe me you would kill for sky like mine. It was much better over to the SE area where there is a town Sevlievo about 4 miles away. They changed the lights about 3 years back to these LED type, before this there realy wasn one, even now I can see a 4th mag star in this so called LP, but the targets I have been on lately are over that way.

Alan

[steppenwolf]

Just for comparison, Alan, here is the image that I produced using PixInsight and its Dynamic Background extraction process with no tweaks to the levels. On this occasion, I prefer the PS version to the PI version:-

[alan potts]

12 minutes ago, steppenwolf said:

This background does have quite a gradient to it and this is simply caused by light pollution. I use PhotoShop for most of my image processing and when I get a gradient like this, I use a plug-in called AstroFlat Pro which was written by Noel Carboni to correct it. I have applied this plug-in to your image and this is the result with a slight tweak to levels:-

Thanks Steve, I can see I will have to get this. I don't have very much LP at all this is why I find it so difficult to understand, the only area where I have any is to the SE and this is in the East. I imagine the low down glow from the Town's LED lights must extend higher than I thought. When I shoot to the West as I have just checked, there is not the same effect, though this was based on only two targets..

Alan

[alan potts]

2 minutes ago, steppenwolf said:

Just for comparison, Alan, here is the image that I produced using PixInsight and its Dynamic Background extraction process with no tweaks to the levels. On this occasion, I prefer the PS version to the PI version:-

I use PS CC, and I will get this plug-in, I have actions though I do not use, think I may well add another hour tonight as this weather just keeps on, they say snow next week, it's 28 outside.

Alan