10×42 vs 10×50 birding binoculars: same reach, different carry and exit pupil geometry
10×42 vs 10×50 binoculars for birding is a same-magnification decision, so both configurations give the same nominal 10x reach. The useful difference starts with the objectives: 42 mm produces a 4.2 mm geometric exit pupil, while 50 mm produces 5.0 mm, but that arithmetic alone does not prove that every 10×50 will look brighter than