Help! How can I get rid of these Gradients?

[Stub Mandrel]

I have hit a brick wall. At the moment my local road lights are switched off while they wait to become LED lamps. Instead of improving my images, this has ruined them, as the fairly gentle LP gradients used to be easy to remove.

Now I get a strong glow from the north-east and any detail in the top- left hand side of my images is washed out by LP while the bottom right is fine.

It isn't light overspill - I added a foot-long flock-lined foam dewshield and flocked opposite my secondary and made sure all lights that could  shine inside the dewshield were switched off all night. I'm sure it is LP as it gets worse as I head east and

Gradient exterminator will get rid of the overall gradient, but it loses all the detail on the polluted side of the image while the other side sparkles with stars!. Worse still, it creates artefacts along the line of the gradient, sometimes one band, sometimes several, depending on how I process the image. This is two hours of 1-minute subs, stretched to show the problem - this is after using gradient exterminator, which adds the banding:

Is there a possibility that I'm doing something wrong in DSS?

[Stub Mandrel]

Phew!

The stripes were caused by using the flat for a 135mm lens instead of for the 130P-DS.

[wimvb]

Problem solved then?

It would certainly be strange if switched off lamps can cause more difficult light pollution.

[Stub Mandrel]

12 minutes ago, wimvb said:

Problem solved then?

It would certainly be strange if switched off lamps can cause more difficult light pollution.

Hopefully, although it seems odd to have a bigger gradient with less pollution! I think the flat mismatch was stopping the gradient removal doing a good job. The end result is here:

 

[Waldemar]

You can not reuse your flats. As soon as you change anything even just taking of your scope cover, dust particles will get in and settle somewhere, creating a need for new flats.

Darks and bias, no problem, but flats need to be made new everytime you change a filter or anything else.

[wimvb]

5 minutes ago, Stub Mandrel said:

Hopefully, although it seems odd to have a bigger gradient with less pollution! I think the flat mismatch was stopping the gradient removal doing a good job. The end result is here:

 

Just found your image. It looks fine to me (on my mobile phone). Must have a closer look later from my laptop.

[Stub Mandrel]

19 minutes ago, Waldemar said:

You can not reuse your flats. As soon as you change anything even just taking of your scope cover, dust particles will get in and settle somewhere, creating a need for new flats.

Darks and bias, no problem, but flats need to be made new everytime you change a filter or anything else.

Not convinced! - but I keep my DSLR very clean, there's just on annoying spot inside the chip cover glass ;-)

Hows this for a flat? (fully stretched):

 

[Waldemar]

Flats are not just about your DSLR... also about dust on filters and lenses and vignetting.
I don't have to convince you, it is just a heads up.

You will find out anyway...

[Stub Mandrel]

7 minutes ago, Waldemar said:

Flats are not just about your DSLR... also about dust on filters and lenses and vignetting.
I don't have to convince you, it is just a heads up.

You will find out anyway...

I make new flats every time I change the imaging train, but I just generate one master flat a month for my 'standard' setup - as you can see vignetting isn't an issue with the 130P-DS and dust at the filter end of the coma corrector isn't going to create dust bunnies.

[wuthton]

1 hour ago, Stub Mandrel said:

I make new flats every time I change the imaging train. 

This is what I do. If a dust bunny appears then I take a new set. 

[wimvb]

That certainly is (ehh) ... flat.

I'm in the habbit of taking flats (approx 10) after each imaging session, since I have to take everything down. Flats are easy and don't take much time.

BTW, about the light pollution mentioned earlier. With street lamps, LP is equally bad over the entire image. Without street lamps, LP is more local in the image. The first situation would create a more even lightness in the image, while the latter can create more of a gradient. So , turning local lights off, may make LP more difficult to remove. Just a thought.

[Stub Mandrel]

13 hours ago, wimvb said:

Without street lamps, LP is more local in the image. The first situation would create a more even lightness in the image, while the latter can create more of a gradient. So , turning local lights off, may make LP more difficult to remove. Just a thought.

That does seem to be my situation. What's happening is I am stretching the images more, also I am imaging further east than normal.

Normally I get stars down to about mag 16.5 yet looking at a picture from the other night I could just find stars that were mag 17.95. Obviously stretching to find these is going to massively exaggerate any remaining LP gradient.

[alacant]

Hi. I understand that removing mercury and sodium light pollution is a case of blocking those parts of the spectrum, but leds not.  Thinking, even though leds will cover all the spectrum, since that is constant and will be falling on every pixel, will it be possible to remove pollution due to leds too I wonder? TIA.

[MARS1960]

1 hour ago, alacant said:

Hi. I understand that removing mercury and sodium light pollution is a case of blocking those parts of the spectrum, but leds not.  Thinking, even though leds will cover all the spectrum, since that is constant and will be falling on every pixel, will it be possible to remove pollution due to leds too I wonder? TIA.

The sodium lights on my street (in particular the one by my back garden and less than 20ft from my imaging rig) were a real pain, so i bought my cls clip in filter which helped enormously.

2 months ago they were replaced with LED's. One night whilst imagining i forgot to replace my filter but because the displacement of light is directed downwards in a small pool it was not a problem.

I can also see more stars above my street lights now. My cls filter still helps with sodium lights over the town but i'm happy with the new LED's, less pollution due to directional beam and more stars.

If it wasn't for the sodium lights over the town i would no longer need an LP filter.

[Stub Mandrel]

Curses! You've jinxed me - my latest session is affected by a pair of dust bunnies, just done a new set of flats...

[iapa]

On 04/10/2016 at 14:35, Stub Mandrel said:

Not convinced! - but I keep my DSLR very clean, there's just on annoying spot inside the chip cover glass ;-)

Hows this for a flat? (fully stretched):

 

If I said "adequate" would i get banned form the forum :)?

 

[Stub Mandrel]

There is a spot at top edge, near the left

I've had to do a new flat now because after showing off my camera got a dose of dust lurgy :-(