There's a guy at my club that I shoot M1Garands with in Camp Perry style open sight competition and he's been to Camp Perry alot and has won some medals. He learned there and has purchased this briefcase he bought somewhere with about 30 lenses in it, and he changes them based on what he needs by popping the lens out and swapping another in. It didn't cost a fortune either. It's a system for adjusting his sight to whatever magnification and light that suits him best on any given day. Open sight shooting...
A real nut according to my optometrist!
You can aslo go to an optometrist if he's knowledgeable about shooting and if he is, what's best for you.
Or you can be like the guy at my club? Want me to ask him where he got the get-up?
Ed