pesphoto
Veteran
That was the only thing about the Fed 2 that bothered me. Loved having the diopter, but it just wouldnt stay put when I adjusted it.
mnmleung
Established
Might be a really silly idea ... how about using those transparent sticky round things that stop cupboard doors from slamming? Stick two to wedge the diopter lever after you have adjusted for your eyes. You can probably peel them off easily. I haven't tried it myself.