Thank you for your comments. Greatly appreciated. It is good to know that I am going in the right direction
I have taken quite a few wide-fields in the last several months and this is the best one so far.
Regarding the lens, the crop is 1.5 for my digital camera (due to smaller CCD size than 35mm film), so I am effectively using a 75mm lens compared to film. I did some test shots and at 10s trailing becomes just visible at full camera resolution.
The posted image has been reduced in size and you can't see much of trailing. In the full size, the middle shows only minor, hardly noticeable trailing, but all edges show elongated stars towards the centre of the image (coma).
I have to step down the lens more to hopefully get rid of it but then I will be losing light.