DSS issue - What is this !?

[halli]

Recently had a go at IC405 - Flaming star with a 1600mm - cool and TS71 refractor.  Everything looked ok and I stacked about 50x200s subs in Ha and the result was very good.  

Went onto the red channel and stacked around 12x200s  subs and the result was as below ! This is simply just the lights. 

I also included bias , darks and flats and the result was still the same.  

The bottom part of the output appears blurry and hasn't stacked properly - the stars are smudges -  whereas the rest is ok - weird !  The subs appear to be ok.  

Has anyone seen this effect before please and can give me a clue about how to fix it ?

Thanks in anticipation

 

[uhb1966]

Well, my first thought was something in the light train not 100% on axis, but the part on the extreme lower right and the extreme lower left seems ok... i'd double check every single light frame of the 12 for obvious defects?!

[Owmuchonomy]

Yes, several of us have experienced this.  I call it 'melt'.  In my case it was my set of flats that caused it.  I had to take a new set and then it was fine.

[halli]

Thanks for your input guys.    I believe Ive found what caused it - one rogue sub where the scope had moved such that some trees had got in the way .  I thought I'd taken them all out !  Just goes to show how important it is to examine all subs diligently for material defects.

I have discover Blink in PI which is quite useful for this purpose  - and using a 1600mm-cool tends to produce a lot more Subs !

Thanks again

[halli]

Well at least I thought it was the above, however I still got variable results with the defect appearing again even after removing the duff sub !  

I found that I needed to close DSS and start up again and then everything was ok for a time and then the defect would appear.  

I even removed and re-downloaded and re-installed DSS and it worked properly again.  I am finding that to cure this I need to re-start DSS.  Pretty unsatisfactory but something appears to be marginal wrt the stacking for this particular set of images.  This is the only time this has happened so hopefully its something to do with this set of data !      Perhaps this will help someone else with the same issue.