Thanks Peter, Tankie and Skippy for the info and tips.

Skippy is completely right when he says ; 'The rear lens assembly is two lenses screwed together and sometimes the inner lens is loose and needs to be nipped up to the rear lens', exactly what's occurred and what I did.

Quite agree Peter, its my optics/eyes I'm trying to get in focus with the SUIT... and at my age (60) my eyes aren't ever going to be fixed! Whereas in the workshop the adjustment had to be defined and precise because it was going to an anonymous, younger user with reasonable eyesight anyway, I just focus it for myself and adjust accordingly.

And, as Peter will tell us, it doesn't actually improve the shooting. I've always had just as good (usually better) results with the iron sights (hythe) as the SUIT.

Cheers