Strange noise... any clues?

[StargeezerTim]

Hi all,

This is a stacked image from last night. its 20 x 5 min subs, iso 1600, Canon 100D, UHC clip filter, 72 ED-R scope. I have just done a couple of light stretches and some contrast to highlight the problem.

I've not had a problem like this with the 100D, and the banding will not be improved using Noels horizontal or vertical banding actions.

Any ideas what caused it and how to 'treat' it?

It seemed fairly clear last night with negligable cloud. All the subs score well on DSS and look OK...

 

[MarsG76]

Looks like it might be thermal noise, did you have a particularly warm night?

 

[StargeezerTim]

32 minutes ago, MarsG76 said:

Looks like it might be thermal noise, did you have a particularly warm night?

 

About 18c i think. A bit cooler than two nights prior when i imaged with the same camera and lens without this effect.

[michael8554]

Hi Tim

I think this is "Walking Noise", and I believe it is reduced by "Dithering" between exposures.

Michael

[wimvb]

Indeed: walking noise. Careful calibration can reduce it, but the best remedy is dithering.

As for these images, optimise your dark frames and use cosmetic correction (available in both DSS and PI) to remove outlier pixels. Then use aggressive pixel rejection during stacking.

[triton1]

"Walking noise","Dithering" I'm just getting over what a "cold finger" is,my head hurts☠️

[wxsatuser]

You could fix your drift, sort out PA or flexure if you have it.

The Lacerta dithers, surprised you don't use it, as it's fairly straight forward.

[StargeezerTim]

1 hour ago, wxsatuser said:

You could fix your drift, sort out PA or flexure if you have it.

The Lacerta dithers, surprised you don't use it, as it's fairly straight forward.

I did dither!

[wxsatuser]

7 minutes ago, StargeezerTim said:

I did dither!

That's surprising, would have thought it would help.

[StargeezerTim]

35 minutes ago, wxsatuser said:

That's surprising, would have thought it would help.

I'm just trying stacking again with hot and cold pixels removed to see if that does anything... 

 

7 hours ago, triton1 said:

"Walking noise","Dithering" I'm just getting over what a "cold finger" is,my head hurts☠️

Tell me about it!

[wxsatuser]

Might be a good idea to find the source of drift, PA or flexure and try to eliminate it.

How often are the Lacerta guiding lights on, do they flash rapidily or very little?
Whats the Lacerta guide graph look like?

[StargeezerTim]

39 minutes ago, wxsatuser said:

Might be a good idea to find the source of drift, PA or flexure and try to eliminate it.

How often are the Lacerta guiding lights on, do they flash rapidily or very little?
Whats the Lacerta guide graph look like?

Removing pixels didn't work. The guiding was unremarkable. My hunch is that the atmospheric conditions were not great and that it doesn't help imaging this area in twilight. Having said that, I did image nearby (Elephant) a couple of nights earlier with no problems. There is also little colour in the image with no nice blue hue to the iris. I think I'll put this down as a one off and try again when conditions are better. That is what comes from trying to image near to the longest day!

[cuivenion]

Did you use a sigma clipping stacking routine in DSS? I think that is the most effective routine when dithering.

[StargeezerTim]

15 minutes ago, cuivenion said:

Did you use a sigma clipping stacking routine in DSS? I think that is the most effective routine when dithering.

Yes... I think it was the atmospherics... I did produce an image but not a good one! I think this bit of sky is better imaged in Astro Dark.

 

[ollypenrice]

I think this is essentially an electronic artefact. If the sky wasn't particularly transparent then you might have had to stretch harder than usual, bringing the artefact into play, when usually you don't.

You can very easily use Noels's anti-banding actions to heal much of the damage. Simply rotate the image till the streaks are vertical or horizontal and apply the appropriate action.

Olly