Thanks mark, it is bk7.
Nothing i can do i suppose about that... Houghy was suggesting i could use some sandpaper to straighten it out a bit to fix the overcorrection!
according to
http://legault.club.fr/collim.html
Tonight, i will try a single star in the belt of orion around mag 1 @ 208x and then try and centre it.
Then a mag 2 star at 1000x and do the intra focal and extra focal