Changing conditions over night

dhickey

Member
Oct 3, 2017
10
0
Attached is a screenshot of the median values of M57 in Subframe Selector. I live in a heavily light polluted area where it is darkest (if you can call it that) towards the east and up to the meridian, then rapidly gets brighter on the west side as it nears the light dome over Baltimore. You can see that in the graph as it starts around 3100 ADU and ends up at 5000 ADU a few hours later. This is typical of the area, it wasn't due to high clouds rolling in overnight. What is the best tool / technique in PixInsight to handle a set of data like this? I've experimented with Local Normalization, which certainly flattens the values across the entire data set. And I've tried just integrating the stack and letting DBE handle it. I can't say I've noticed an appreciable difference in those two methods.

The true solution is probably to only image up to, or slightly past, the meridian (or move to the desert).

Thanks,
Dave
 

Attachments

pfile

PTeam Member
Nov 23, 2009
5,603
102
i am in much the same situation, and the two solutions you mention are pretty much it. i find that i have to be very careful with LN lest it introduce artifacts - need to tune the scale parameter and make sure that i'm starting with a very clean reference, which is usually just a careful DBE of a non-LN integration.

sometimes if i can't figure out what's background and what's not, i'll cheat by finding a high quality image on astrobin, register it to my FOV using StarAlignment, and then place the DBE samples on that nice image. you can save a DBE process icon and then quit DBE, foreground the target image, and double click the process icon. from there i tune the sample tolerance and go.

rob
 

1DegreeN

Active member
Jan 12, 2014
25
1
I know you're shooting on a mono camera but have you considered using an LP filter for your Lum? I can't vouch for it myself but I've seen it suggested. I do use an LP filter with my OSC and it is very effective.
 

dhickey

Member
Oct 3, 2017
10
0
i am in much the same situation, and the two solutions you mention are pretty much it. i find that i have to be very careful with LN lest it introduce artifacts - need to tune the scale parameter and make sure that i'm starting with a very clean reference, which is usually just a careful DBE of a non-LN integration.

sometimes if i can't figure out what's background and what's not, i'll cheat by finding a high quality image on astrobin, register it to my FOV using StarAlignment, and then place the DBE samples on that nice image. you can save a DBE process icon and then quit DBE, foreground the target image, and double click the process icon. from there i tune the sample tolerance and go.

rob
Thanks. Yes, I've found some objects have needed a scale of 128 and some work better with 256.

Dave
 

dhickey

Member
Oct 3, 2017
10
0
I know you're shooting on a mono camera but have you considered using an LP filter for your Lum? I can't vouch for it myself but I've seen it suggested. I do use an LP filter with my OSC and it is very effective.
Yes to a mono camera, but I haven't considered using an LP filter. I figured that would knock things down too much on broadband objects like galaxies. Might be something to consider, although more of the munincipal lighting in my area is becoming LED-based.

Dave