Was out imaging the other week and after taking a shot whilst the camera was processing I began to slew the scope to another target when the shot came through I seen this and thought what the......
The only stray light it could have been was possibly the moon which was only just above the horizon and as the scope slewed it was at least 40 deg away if not more,I was baffled but thought wow... oh well it looks interesting.
Now that you mention it, your probably right, but I had released the shutter and even though I try to keep light away from the camera whilst processing (with custom function noise reduction on) I thought that the shutter would still be closed.
but I had released the shutter and even though I try to keep light away from the camera whilst processing (with custom function noise reduction on) I thought that the shutter would still be closed. 
What a dill I am, I should have known that.
thanks for the laugh 
