Any help greatly appreciated

[Digz]

As the title suggests really.

Last night I was out with my wide-field rig to give it a proper run since it was built. My target was the area of Orion's belt as there is a lot of interesting stuff going on around there.

A rather frustrating night in all which started with PHD not working on my netbook.....one for another thread! I ended up having my MBP outside to get everything running and using my netbook inside to monitor it all via teamviewer.

Anyway I eventually got everything set up and working and left the camera to take 18 x 10min guided subs.

I was hoping to get something semi-decent from last nights foray but am really disheartened at the results and would greatly appreciate some help and advice.

Info:

Nikon D7000

ISO 800

Nikkor 105 Macro Lens set to f4

10min subs

Guided with PHD and finder guider

Issues, issues, issues....

It was windy with some strong gusts last night but my guiding appeared to be reasonable. Despite that the first 9 subs were showing oval stars, but the last nine were quite round. Maybe I am suffering from flexure? But that can wait.....and there is enough info here which I have read which can help me sort out any flexure.

I am disappointed in the resultant stack of images from DSS as it is showing a massive gradient which is circular and whenever I use my DSLR I get this problem - its this I would like some help on.

As such I have had a frustrating afternoon trying to process the image and have ending up in a right mess. Its probably not helped by the fact that I dont really know what I am doing in DSS, but some help in diagnosing what is causing this would be great. The above IIRC was stacked in DSS using the median settings, I am about to try some other settings but Im not sure if this will actually help.

So anyone have any ideas on what might be causing this? My initial thoughts are maybe light leakage from the viewfinder i.e. stray light entering through here? I do have a cover for this which I forgot to try.....D'oh. But any thoughts you guys may have are more than welcome!

TIA.

BTW the blown out nebula is not an issue, I know how to resolve this, Im just keen to get the gradient banished! I have tried tutorials from here (Gradient Removal) which seem to remove the gradient but leave the stars really grey, I guess I can edit my way out of the problem but it would be good to know what the initial cause is.