Hi Chris
I use an SRB sleeve type adaptor. It is very similar to the Eagle eye and London Camera Exchange adaptors. I used to own a LCE one, I hated it and ended up chopping it up and adapting it! The SRB one is also only £35 that's right
ONLY £35. It screws on to the filter thread and fits very snuggly over the eyepiece. It comes with 3 screws, though only one is needed (due to the excellent fit) and is finished in black. The general build quality is superb. Have a look at their website
www.srbfilm.co.uk
Regards
Mark