Thanks again for the information.
The new filter arrived today, I will put it on tomorrow and see if there's any difference between the two.
I have a good sturdy tripod and leave a two second timer between button press and exposure to avoid any shake from me. I actually didn't use mirror lock up and forgot all about it.
I think the irregular shaped stars are my fault. I think in post processing I upped the clarity (its not clarity, I can't remember what it's called now) too far. I will have another look later.
Also I think I took one in the same position with ISO 1600 so will have a look at that one too.
I know for sure if I go longer than 20 seconds the stars start to look like little white ants!
At anything less than ISO 1600 and it picks out almost no stars.
Probably what doesn't help is the fact I'm using a crop sensor DSLR.
I know it's not good taking photos with the moon out but clear nights being unpredictable and me being impatient made me want to try anyway.
