The benefits of mounting two of them side by side for binocular vision appear to have been discussed almost since the telescope's discovery in the 17th century. Galilean optics were used on most early binoculars; that is, a convex objective and a concave eyepiece lens were used. The Galilean design has the benefit of displaying an erect image, but has a narrow field of view and can not be magnified very highly. In very affordable versions and in opera glasses or theater glasses, this style of construction is still used. In low magnification binocular surgical and jewelers' loupes, the Galilean style is often used because they can be very short and create an upright image without additional or irregular erecting optics, minimizing costs and total weight. They still have wide escape students, making centering less important, and in such applications, the narrow field of view fits well. Usually, they are mounted on an eyeglass frame or custom-fit on eyeglasses.