what could be causing this?

[Rustang]

I'm doing the same editing process of stretching in the same way but I'm now stretching more data and now seem to be getting these strange darker areas!. Does anyone know whats causing it? 21x 120 sec lights, 20 X bias, 20X  flats, stacked in DSS Nikon D750, SW 130PDS. As you can see there is nothing on the single 2 min sub!

 

[wimvb]

1. Check the calibrated unstacked subs (dss has the option to save these). If it's there, it's the calibration that causes it.

2. Stack without pixel rejection.

In pixinsight this is common after background equalisation, if samples covered bright stars. But that doesn't seem to be the cause here.

[Sunshine]

Sorry, I cant help with your question, but I will add that in high school I drove a rusted old Mustang and, my girlfriend then (now my wife...oh god has it been that long) called it the "Rustang" she still brings it up 25 years later.

[RT65CB-SWL]

I think Nikon have had a bit of a poor reputation with astrophotography... and I have a Nikon D80 and two old digital compact cameras.

...and I was going to say: "Oh look, he's got an image of two black holes!" 

[Rustang]

4 hours ago, wimvb said:

1. Check the calibrated unstacked subs (dss has the option to save these). If it's there, it's the calibration that causes it.

2. Stack without pixel rejection.

In pixinsight this is common after background equalisation, if samples covered bright stars. But that doesn't seem to be the cause here.

Thank you, I will look into it although I've not changed any settings since using it with shorter subs, hopefully I've not waste two hours of shooting! 

[Rustang]

2 hours ago, Philip R said:

I think Nikon have had a bit of a poor reputation with astrophotography... and I have a Nikon D80 and two old digital compact cameras.

...and I was going to say: "Oh look, he's got an image of two black holes!" 

Are Nikons not used then because things like this appear!? 

[Rustang]

3 hours ago, Sunshine said:

Sorry, I cant help with your question, but I will add that in high school I drove a rusted old Mustang and, my girlfriend then (now my wife...oh god has it been that long) called it the "Rustang" she still brings it up 25 years later.

Rustang for me is because I'm Russ and I've owned 3, that was until I sold the last to get married!