Does the Second Number on a Monocular/Binoculars Matter? (8×42 vs 10×42 Example)

Q: Does the second number on a monocular actually matter? What’s the difference between something like an 8×42 and a 10×42 monocular/binoculars?

A: Absolutely — that second number impacts how bright your view is and how big the whole unit will be.

That number stands for the diameter of the objective lens, measured in millimeters.

• 42mm: Balanced size and light gathering. Great for most sightseeing, overcast days and golden hour.
• 50mm: Brighter image in low light conditions, but noticeably bulkier and less pocket-friendly.

For city trips and travel through airports, 42mm is the comfort zone. Most of your sightseeing happens in open daylight or under city streetlights, not in heavy shade at sunrise.

If you plan to spend evenings along the waterfront or stroll parks during golden hour and want even better low-light performance, lean toward the 50mm objective lens.

Quick note on magnification difference: 8×42 gives you a steadier, wider field of view that’s easier for casual travel. 10×42 zooms in closer, but hand shake becomes more noticeable, so it takes a little more care to hold steady.