I was told once that the human eye has a pupil around 5mm in diameter, and to get the most light-gathering ability out of binoculars, you want to come as close as you can to that size. You're supposed to divide the bigger number (objective lens?) by the smaller, so 8X42 come out as 5.25, plenty big to give you the max low light capacity. I was impressed with my cheap Alpens until they fell out of my pack onto the carpet, and the objective lens popped out! Next time, I'll be spending the bucks for a decent set of binocs!