Atik 460ex first light- Horsehead Ha advice

[Wailin]

Hi,

Last night was first light for my Atik 460. Conditions were not ideal, heavy light pollution (back garden) and an almost full moon caused strong gradients, very obvious in the below image. I used a Baader 7nm Ha filter. I did not have the required back focus distance of 55mm, it was closer to 60mm. Not sure what effect that would cause, but can't seem to see any big issues with focus (correct me please!). I need advice on flats and how to take them. My normal method with my DSLR is too bring up Microsoft power point and have a blank white screen. I normally aim to have the spike just before halfway on the histogram. With the CCD I found it more difficult and adding flats caused the gradients to worsen. What is the average exposure length used with the Atik 460ex and Is it important to keep the CCD at the same temp as lights? Also, do I need to take darks and bias with the Atik? There is some noise in the image (12 600sec exposures) which I was surprised to see.

Horsehead nebula in H-alpha by Wailin..., on Flickr

Equipment: Skywatcher ED80, NEQ6 mount.

Thanks folks.

[johnrt]

Not a bad start, your corner stars are showing signs of elongation, are you refering to the chip to reducer distance being out when you say not at 55mm but nearer 60?

Take flats as you would with a DSLR, I use a blank text document on my iMac screen. Aim for a saturation of 23,000 ADU with the 460ex and that will get you the right exposure for making a master flat. Don't forget to subtract the bias from your flats before combining them to a master for use in calibrating the lights.

[Wailin]

Not a bad start, your corner stars are showing signs of elongation, are you refering to the chip to reducer distance being out when you say not at 55mm but nearer 60?

Take flats as you would with a DSLR, I use a blank text document on my iMac screen. Aim for a saturation of 23,000 ADU with the 460ex and that will get you the right exposure for making a master flat. Don't forget to subtract the bias from your flats before combining them to a master for use in calibrating the lights.

[Wailin]

Not a bad start, your corner stars are showing signs of elongation, are you refering to the chip to reducer distance being out when you say not at 55mm but nearer 60?

Take flats as you would with a DSLR, I use a blank text document on my iMac screen. Aim for a saturation of 23,000 ADU with the 460ex and that will get you the right exposure for making a master flat. Don't forget to subtract the bias from your flats before combining them to a master for use in calibrating the lights.

Thanks John, yes I am referring to the chip to focal reducer distance. Is this why the stars are oval? I don't have the correct spacers yet.