help with dark circle only with RGB filters

[jahnpahwa (JP)]

G'day team,


I wonder if anyone else has come across this?



I was stretching RGB channels last night and have found a dark circle seen bottom right quarter here. Its with an asi1600mm pro camera, efw mini filter wheel and 1.25" filters. I went back and its present across both of my OTAs, but I cant see it, even way over stretching my narrowband images. MY guess is that its a reflection? It looks to actually increase SNR, though, which is strange. Its in the same spot on all three channels.


Any suggestions on how to avoid it would be great!

[Xeteth (David)]

Looks like a dust mote, however it's weird that it is present across both OTA's.... so you might be right with reflection? Someone with more experience can probably give a better answer.

[jahnpahwa (JP)]

Originally Posted by Xeteth

Looks like a dust mote, however it's weird that it is present across both OTA's.... so you might be right with reflection? Someone with more experience can probably give a better answer.

Thanks David, yep there were some specs of dust around filter wheel and sensor window, have airblasted all of them this arvo. It may be there in thr NB channels too, but its just cut so hard to see.

[PKay (Peter)]

Hi JP

It is an interesting exercise to create a Master Flat image and have good look ( you will have to stretch to see it) . This one I did yesterday.

[glend (Glen)]

It may simply be dirt inside the camera sensor compartment or on the surface of the AR Window. This would have it appearing in any filter. I wouild remove the filter wheel and inspect the sensor window area. Personally I always fund flats a lazy imagers tool, if your Optics are clean (and I mean filters, camera etc, you don't usually need flats, especially with the 1600.