Dark subtract problem

[Astrobobo]

Hello all,

I'm new to the forum, but I've been into astrophotography on and off for quite a while. Still, I have silly problem I can't find the answer to - my master dark won't get rid of all the bright columns on the CCD. I'm using a STL-11000. I tired cosmetic correction, but it doesn't work, I'm left with those really prominent bright columns.

If someone would like to have a go, I'd really appreciate it. I've included the master dark and one L light on this link: https://drive.google.com/open?id=0B42bW-rSyIhrUEJLQzlCZDdBd2M

Thanks and greetings from Croatia!

[chris.bailey]

Try Cosmetic Corrections Use Defect List section and add columns 426, 527, 3428, 3596 and 3614. That gets rid of any residual from dark subtraction.

Chris

[Astrobobo]

Thanks, sorry for the late reply. It actually works!

I'm still at a loss why the dark frame didn't get rid of those in the first place.

[chris.bailey]

I'm still at a loss why the dark frame didn't get rid of those in the first place.

One of my CCD's has similar defects and darks don't fully correct them either. I "think" it has to do with the pixel values in the defects varying quite a bit from frame to frame. With a master dark those values are averaged so when subtracted there are slight residual variances.

Glad CC worked for you. Adding a large dither on capture can help too.

Chris

[Astrobobo]

One of my CCD's has similar defects and darks don't fully correct them either. I "think" it has to do with the pixel values in the defects varying quite a bit from frame to frame. With a master dark those values are averaged so when subtracted there are slight residual variances.

I'm not so sure...those columns are really bad.