Crab Nebula Image

[wouterw]

Hello,

Below is a link to an image of the Crab Nebula, which i took from my backyard with moderate light pollution. This final image consists of about 96 light frames of 5 minute exposures ISO 400 together with 34 dark frames of 5 minute exposures and ISO 400 stacked and aligned using DeepSkyStacker. Details of the equipment used:

Telescope : Skywatcher D = 120mm F = 1000mm

Camera: Canon 1100D

Autoguider: Meade DSI III using ASTRO-TECH 65Q telescope

Light Pollution Filter: HUTECH 2'' IDAS LPS D1

I did a little image processing on the image below in Gimp using levels, curves and hue-saturation.

https://lh4.googleusercontent.com/-AW3l4Glo2JU/VPL8b9TeAJI/AAAAAAAAAcM/V8lmWiM-Ryo/s1152/CRAB%2520NEBULA.jpg

I'm just wondering why the background seems scratched in some places and also why it's so much brighter in some regions than other. Are there any why to prevent or remove this ?

Thank you.

[redmoo]

Hi there and welcome to SGL!

That is pretty normal for deep sky images. A things that helped me when starting out:-

Use a higher ISO:- I think most people suggest either 800 or 1600. I have the 1100d and find that 1600 works really well.

Shoot flat frames:- This will sort out the gradient that you are seeing. Flat frames are basically a baseline picture for your imaging train. You shoot a flat white light source (there are many different ways of doing this) and then DeepSkyStacker creates a 'flat' light image and then processes these differences out of your actual images. It will also take care of a lot of dust motes etc, but the picture seems pretty free from that. 

In order to shoot the flat frames correctly, you need to do it without removing the camera from telescope....or anything from the telescope for that matter!

Good luck!

[Thalestris24]

Hi

+1 for taking flats and darks. There seems to be some 'halos' around some of the brighter stars. I'm not sure which particular scope you have? If it's an achro the halos could be CA. Or they could have been caused by a hazy sky. Unfortunately you seem to have jpg artefacts - posting an image as .png is better

It might also be that your light pollution is very bad in certain directions. If you can avoid it or find some darker skies, that's better than relying on a lp filter. I have similar problems myself which cause nasty gradients. There are techniques around for removing them - maybe post again on the image processing section You can get also advice from some experts on here on how to keep and improve star colour.

Louise

[DaveS]

Do you have a field flattener? Pretty much essential when imaging with any refractor that isn't a high-end dedicated flat-field astrograph.

Also some of the banding could be due to 8 bit processing in Gimp, you really need to be working in 16 bit after stacking.

[Thalestris24]

I think the recent development builds of Gimp support 16 bit processing: http://nightly.darkrefraction.com/gimp/

At your own risk though!

[wouterw]

Hello,

Thanks for all the comments and advice. I'll look into it.