I haven't seen anyone using a scope doubler since the 70's. It was common to convert Lyman 10 power scopes to 20 power with a few of us benchrest shooters in Calgary. I think the fellow doing it was in Washington. Damned if I can remember his name, not that it matters, he is long gone. JUST REMEMBERED . . . Walley Siebert. Great guy, really knew his optics.