Hello all
Typically when I see these black lines (see attachment) in calibrated images, it tells me that I need to refresh my darks and/or bias frames.

However, despite a whole new set of darks and bias frames, this black column remains....I can see this and many other 'defective' columns in the raw light frames, and all of them seem to subtract out except this one.

Of course, it has to be right in the middle of the frame. I am out of ideas on how to remove this...any suggestions please?

This is an STL11K camera.
thanks
Martin

Hi Martin,

It would help if you could post the following FITS:

1) An uncalibrated light image

2) a single matching dark frame (not a master dark) taken within a few days of the light.

3) (optional) a bias frame.

To save bandwidth, load all frames into CCDStack then crop around the defect, save as unsigned 16 bit FITS.

Stan

Hi Stan and thanks for your help.
In my post, when I said 'a whole new set of darks' I was referring to a master dark created from 17 dark frames on 19 Jun...thinking that was recent enough.
I took a single fresh dark frame at the end of last night;s session, calibrated the same image, and the line has gone. So clearly, the changing characteristics of my camera...or the manner in which the master dark frame was created (in CCDStack) has caused this....but it seems okay now.
thanks again
Martin

Hello Martin,

I also have an STL camera with a couple of cold column defects. I have tried stacking with several programs, including CCDStack, and they not only remain, but multiply because I dither my exposures. To solve the problem I wrote a small freeware program to fix all the exposures automatically. The programs makes calls to the CCDSoft column fix routine. The columns must be fixed before registration and can be done before calibration. To use the program you must first start CCDSoft and then run my program, PicFix.

Here a link to the download page for PicFix.
http://bf-astro.com/software.htm

Hope this helps,
Bob Franke

Hi Stan
further to my last...I tried 12 of the dark frames used for the master I created on 19 Jun...and each one of them leaves that line behind....so it certainly isnt CCDStack.
I have ditched them now, and started a new library.
cheers
Martin

Same problem here!

For the first year I was able to use dark library for my STL-11K but just recently it all changed. Now I have to take darks after every imaging session in order to calibrate properly. I also dither my images and know the pain of wide black column after stacking the images.

If I'm using darks from previous night I have to do column repair before stacking.

This problem only applies to one column at the middle of the sensor

If you are dithering then it should be possible to data reject those columns. Try using Poisson Sigma Reject; drag a rectange around the defect area; check the "apply to selection" box; use an agressive factor (e.g. 1 or maybe even less) until the images show that line as red (rejected).

Stan

With dithering, there is a fixed pattern to the dither that ordinarily will not provide sufficient separation for column defects, unless the dither amount is set considerably high.

There is a private option in CCDAutoPilot that uses a specific dithering pattern for column defects. If interested, please inquire on the CCDAutoPilot support forum for details so that the reply may benefit others.

I have similar problems with cold column/pixel defects in my STL11000. I make a fresh set of darks every month, usually 4 or 5 acquired each evening of imaging, which is so easy to do with CCDAP. On cloudy nights when no rain threatens, I'll do a full set of 20. This, along with dithering, eliminates these problems at least with my particular camera.

Somewhere I read that thermal cycling modifies the characteristics of CCDs although other cameras don't seem to be so seriously effected as the 11000. I guess it's just more susceptable to these effects and we definitely do a lot of thermal cycling of our devices.