Iris
I agree with Tim, in fact, I'd be even stronger!
Indoors, for air, a basic 0.8 to 1.8 iris is all you need, any thing else is an unnecessary complication.
"Most of the kit in a fishing tackle shop is to catch fishermen not fish", a lot of shooting kit is the same!
I know a lot of top class shooters, who even in out door full and small bore, who see any thing other than a basic iris as some thing else to get wrong or complicate a simple operation, and I'm married to one of them, her philosophy is KISS, "Keep It Simple Stupid."
If you want to spend your money though, our favourite iris is the Centra Crystal, small, and great light gathering.
Have Fun
Robin
Walther KK500 Alutec expert special - Barnard .223 "wilde" in a Walther KK500 Alutec stock, mmm...tasty!! - Keppeler 6 mmBR with Walther grip and wood! I may be a Walther-phile?