I use a Kowa ts-501 20-40xzoom. It's 50mm. Works well at 20x indoors at 25 yards and can zoom to see .22 cal at 50 yds outdoors. It can't pick up the ones that miss the paper though! Does't include tripod, but mounts well on a
Gun-ho box with a Gil Hebart mount. Nice and short, so it leaves lots of space in your box. My $.02. Good shooting.