NGC4038/9 Antennae Galaxy

[telecasterguru (Frank)]

This is the Antennae Galaxy NGC4038 and 4039.
4x600 seconds and 3x300 seconds Canon 1000D unmodded @ iso800 ICNR on an ED127 at f7.5. Stacked with DSS and I used PS to change to a jpeg file. No other processing.
I am having real problems getting an even background to the image and have tried many different techniques in Photoshop but they all darken the background and remove almost all the detail of the galaxy. Not that there is a lot there to begin with.
Any suggestions on how I can create an even background field without losing detail or is it something that is in the relationship between the camera and the telescope that needs to be dealt with? Would a focal reducer help?

Thanks

Frank

[toryglen-boy (Duncan)]

Frank, the first thing i thought as soon as i seen the thumbnail, even before i opened it up was "flats"

Looks to me like the image is suffering from sever vignetting. Flats would give you an even illumination across the frame.

[multiweb (Marc)]

Frank, the only way you're going to address this is by doing flat fielding and in order to do that you'll also have to shoot bias frames. There are loads of tutorials on calibration so you'll find all the info needed in these forums or google. I believe Baz at ASSIGN has a good tutorial about it.

Originally Posted by telecasterguru

This is the Antennae Galaxy NGC4038 and 4039.
4x600 seconds and 3x300 seconds Canon 1000D unmodded @ iso800 ICNR on an ED127 at f7.5. Stacked with DSS and I used PS to change to a jpeg file. No other processing.
I am having real problems getting an even background to the image and have tried many different techniques in Photoshop but they all darken the background and remove almost all the detail of the galaxy. Not that there is a lot there to begin with.
Any suggestions on how I can create an even background field without losing detail or is it something that is in the relationship between the camera and the telescope that needs to be dealt with? Would a focal reducer help?

Thanks

Frank

[Hagar (Doug)]

Hi Frank, I'm afraid this image is all but unrecoverable. The method Marc mentions is the only way to save future images like this. The amount of data here is quite small and using PS plugins like gradient exterminator etc. just destroys the image. Flats and bias frames are what is needed but must be done for each imaging run or for each image if the camera is moved in the focuser.

Good luck.