But beyond a certain point, the quality isn't apparent except to those who use them under the most demanding circumstances. The more expensive binoculars use high-transmission lens coatings that reduce the amount of light loss. They also employ more distortion-free lenses and higher quality prisms such as the BAK4 type. And they tend to be more durable. The problem is that there are exceptions.
Manufacturers can keep costs down by stinting on quality control.
Some people have gotten pretty good binoculars at very low prices, but another pair of the identical product may give horrible images. Lack of consistent quality is the problem.