the small matter of eyecups. A few years ago, nearly all binoculars
accommodated eyeglass wearers with folding rubber eyecups. But
for birders who share their binoculars, rubber eyecups cause
trouble. Most require a bit of wrestling to fold them up or
down, costing several seconds each time the binoculars change
hands. That can make you miss the bird.
top-quality roof prism binoculars have eyecups that neatly slide
in and out, or they have twist up eyecups, letting the user
dial exactly the needed amount of eyecup extension. Twist-ups
also maintain their position without collapsing at crucial moments.