PI Master Dark Question/Issue

[Ryderscope (Rodney)]

It would be good if I could get some input from the Pixinsight users on the this forum regarding a thread that I have been running on the PI forum to do with issues that I have noted with my master dark frames. The link to the PI forum thread is here..

The summary of the issue is that I have noticed vertical bands in my master dark frames which are not present in any of the individual sub frames. If I play with the pixel rejection settings and drop down the 'high' ranges I can make the vertical bands go away but I would like to understand why they are there and if it matters if I adjust the rejection metrics in this way.

I have uploaded the results of my testing with 300s dark frames to a shared drop box folder if anyone wishes to have a look let me know what you think. There are two dark frames along with the PI process icons used to produce them. Link to shared dropbox folder is here.

Many thanks,
Rodney.

[RickS (Rick)]

Hi Rodney,

I'm very busy for the next few days but will take a look if I get a chance.

Cheers,
Rick.

[Ryderscope (Rodney)]

Originally Posted by RickS

Hi Rodney,

I'm very busy for the next few days but will take a look if I get a chance.

Cheers,
Rick.

Many thanks Rick.

[Ryderscope (Rodney)]

Ok, I have found a number of threads including one here on Cloudy Nights regarding vertical banding on master dark images from a QSI683 which is the same camera that I am using. It seems that this is a common issue. In my case it only seems to come into effect when I am shooting short subs (e.g. 30s) so I can work around it. It is still strange though how it doesn't seem to be apparent in the individual subs but does show up following image integration.

** Edit **
The reason that I am seeing the banding after integration is that the integration process is doing exactly what it is designed to do. It is separating out the weak signal from the background and bringing it forward.