How do I pick the right objective lens?
The size of the objective lens is measured in millimeters and is usually indicated in the binoculars' name. For example, the "Nikon EDG 10x42" has a 42mm objective lens. The larger the objective lens, the more light the binoculars will let in and the better image quality you will receive in low light conditions. However, larger objective lenses can also drive up the price and weight of the binoculars, so you may want to consider how important low light performance is to you vs. budget and portability when shopping. In general, telescopes will have the biggest objective lenses (up to 125mm), but, for hunting, you probably only need between 40 – 50mm and, for other outdoor activities like bird watching, you may only need as little as 20mm.