I picked up one of these guys: So now I can adapt m42 lenses using the same speed booster I bought for my Rokkor's. Pretty cool. And the m42 screw fitting is so snug that you'd never know there are 2 adapters. Feel very solid. My first m42 lens is a Pentax SMC Takumar 200mm F4. Wide open the chromatic aberration is pretty shocking, but otherwise it's nice and sharp. Anybody else double adapting?