What a difference a filter can make

I forgot to add (no pun) that you need to be careful about how you combine your calibration frames with you light frames.

Bias (if you need them): subtracted from darks and flat-darks
Darks: subtracted from lights
Flat-darks: subtracted from flats
Flats: divided into the lights

The AAVSO article is pretty comprehensive in describing the processes.

Dave

John - sure - take some flats and apply them to the light frames you already took.

The only issue you may come across is that your focus position *may* have changed since you took the original lights.

The flats don;t have to be taken at the same time or temperature as the lights - the only important factor is taking the flats at the same focus point. If it *has* changed, don't panic. If you can estimate where focus was, roughly, that will be good enough to improve your images.

Another alternative is to digitally compensate for the vignetting. Its not my expertise - others here are far more qualified to comment on the intricacies of using Photoshop et al - but I believe you can, using the lasso tool or similar, alter the levels for different parts of your image. In your case, you could select the vignetted piece of the image, invert the selection then increase the levels of this inverted selection - this should bring the outer portions of your image to level of the central (vignetted) piece. Unfortunately, since vignetting is typically a gradient, it can give somewhat unsatisfactory results.

The first line above is definately a good option for you. I reckon you could take usable flats in less than 30 minutes and really improve your image a huge amount...

Dave

Cropped out the nebula and tried to darken it a bit

Oopps..no image attached

Hi John.

Hope you are keeping well. what can I say welcome to our world the lads gave you some great advice. your processing has come on a lot two. The M42 image is very good well done.

Carl.

Thanks everyone. Looking forward to getting out again with the 450D / CGE this weekend.