Walking noise?

[matt_baker]

Really confused as to what this is in my G and B of M31. Red is completely fine, but G and B seem to exhibit walking noise even though they were all dithered the same amount, same distance and same night.

 

Red

Green

Blue

I do realise that my DBE is rather scuffed on G and B but it doesn't make a difference

[wimvb]

This definitely isn't walking noise, in my opinion. Walking noise is on a single pixel scale. To me this seems more a case of walking dust specks, but they are a bit small to be on the filters. Check your calibrated, unregistered subs. Do they have dark dust bunny-like features, all in the same place? Then register those subs, and compare again.

[matt_baker]

I've had a look at the uncalibrated, registered data and it's definitely there, albeit hard to spot. It's a little black trail as the exposures go on. It's a very odd thing and I was thinking the exact same because it isn't consistent throughout the image, just certain spots, and the fact that it doesn't show up at all of the red data. I'll keep having a look

[wimvb]

Time to open the filter wheel, I’d say.

[matt_baker]

14 hours ago, wimvb said:

Time to open the filter wheel, I’d say.

I honestly can't figure out what it could be. If it was dust then surely it would be present in the red data too? I did 40-50 lights of each filter so it's not like there's less to integrate for it not to appear

Edited November 24, 2020 by matt_baker

[Tomatobro]

Filter wheel changing filters mid exposure?

[wimvb]

If it's on the filter, it will vary from one filter to the next, and may be absent on a certain filter. Otoh, the specks are much too small to be on a filter. In what order did you take the exposures for the different filters? Can you repeat the results, ie, can you take flats for the various filters? One exposure per filter should do it. Is it on all the green and blue exposures? For instance, could it be tiny water droplets that were sitting on the sensor, but have dried up since? In that case, you wouldn't see it any more. And it would vary in size/intensity for subsequent exposures. So by the time you got to the red filter, it could have been gone. I'm just grasping at straws here.

1 hour ago, Tomatobro said:

Filter wheel changing filters mid exposure?

Does that happen? My wildest guess is that that wouldn't create specks, but a swiping vignetting pattern or gradient.

In any case, I would take flats and see if the problem persists, or if it was a one time event.

[matt_baker]

Just now, wimvb said:

If it's on the filter, it will vary from one filter to the next, and may be absent on a certain filter. Otoh, the specks are much too small to be on a filter. In what order did you take the exposures for the different filters? Can you repeat the results, ie, can you take flats for the various filters? One exposure per filter should do it. Is it on all the green and blue exposures? For instance, could it be tiny water droplets that were sitting on the sensor, but have dried up since? In that case, you wouldn't see it any more. And it would vary in size/intensity for subsequent exposures. So by the time you got to the red filter, it could have been gone. I'm just grasping at straws here.

Does that happen? My wildest guess is that that wouldn't create specks, but a swiping vignetting pattern or gradient.

In any case, I would take flats and see if the problem persists, or if it was a one time event.

I went from R to G to B. Only shows up on G and B

[Tomatobro]

My mount is remote from my warm room and I had (amongst other parameters) the voltage at the mount sent back to the warm room and displayed as a live graph on a screen. As a result you got used to watching the voltage dip in various ways as the system operated.

With my Atik filter wheel I would issue a command to change the filter and you would see a certain change in the graph as the task was completed.

During one session I was staring at the console (not much to do while imaging) and I noticed a random voltage dip that looked very like a filter change so I went to the mount and listened to the filter wheel and sure enough it whirred at odd times.

Needless to say the filter wheel has been replaced so yes it can happen

[wimvb]

Gremlins at work.

2 hours ago, Tomatobro said:

(not much to do while imaging)

Netflix or HBO 😄