DSS does weird things to my red channel.

[Martaniu]

First up my gear:

Pentax-KP

Tripod

300mm prime lens

The last few weeks I started to collect data for the orion nebula to try my luck with deep sky photography. As you can see I dont have a star tracker so I took *alot* of very short exposures (0.8s) with ISO 102400. After I took them I took my calibration frames just like I read about on astrobackyards website. I then stuffed everything into DSS, clicked the recommended settings button, set the amount of pctures to stack to 85% and waited. What came out in the end was an RGB image with the red channel just uniformly grey.

 

So I had a look at my red channel in the light frames and there was definetly data there.

So I thought it might have something to do with my calibration frames so I just ran a stack without any. Out came a picture with a nearly completely white red channel. So I decreased the brightness quite a bit and upped the contrast and saw a great white dot in the middle of my picture.

I have no idea anymore what caused this. I checked all my light frames and of none of them have a bright flash or anything in the middle. I dont know what else I could try anymore.

Thanks in advance for your help

 

Small Update

I have used a 24mm for a widefield image at ISO 51200 and after stacking the red channel was completely normal and the picture came out just like I hoped it would. But trying the same nebula (Orion) at ISO 51200 brought out the same error in my red channel as with the first try.
I am getting more and more confused as to what caused this.

Edited February 23, 2021 by Martaniu
formatting

[The Lazy Astronomer]

Can't pretend l know what's happened, but I'm going to throw some questions at you anyway 😁

How many stars did DSS find when you registered the frames? And how many frames did it report it included in the final stack? Do you know the bayer pattern of your camera and did DSS have the right one? (I think RGGB is pretty typical)

[wxsatuser]

2 hours ago, The Lazy Astronomer said:

Can't pretend l know what's happened, but I'm going to throw some questions at you anyway 😁

How many stars did DSS find when you registered the frames? And how many frames did it report it included in the final stack? Do you know the bayer pattern of your camera and did DSS have the right one? (I think RGGB is pretty typical)

I believe the pattern is RGBG and this camera has pixel shift, don't know if this has an effect in stacking.

[Martaniu]

8 hours ago, The Lazy Astronomer said:

Can't pretend l know what's happened, but I'm going to throw some questions at you anyway 😁

How many stars did DSS find when you registered the frames? And how many frames did it report it included in the final stack? Do you know the bayer pattern of your camera and did DSS have the right one? (I think RGGB is pretty typical)

I set the star detection threshold to 23%. With that setting DSS found roughly 50 stars to stack.
It stacked roughly 280~ out of 400 pictures if I remember correctly.
The Bayer pattern is RGBG like Blue Straggler suggested.

Edited February 23, 2021 by Martaniu
Found the info

[wxsatuser]

Think you will find the array is RGBG.

[michael8554]

"Pentax‘s Pixel Shift (Available on the K-1, K-3 II, KP, K-70) attempts to alleviate some of these problems through a novel approach of capturing four images quickly in succession and by moving the entire camera sensor a single pixel for each shot. This has the effect of capturing a full RGB value at each pixel location"

If you have this option selected, the Bayer Pattern is anyone's guess..........

Michael

[Martaniu]

7 hours ago, michael8554 said:

"Pentax‘s Pixel Shift (Available on the K-1, K-3 II, KP, K-70) attempts to alleviate some of these problems through a novel approach of capturing four images quickly in succession and by moving the entire camera sensor a single pixel for each shot. This has the effect of capturing a full RGB value at each pixel location"

If you have this option selected, the Bayer Pattern is anyone's guess..........

Michael

I had a look through my settings and this option is disabled.