A spyglass with a plano-convex lens that focuses at 12 ... But this made the focal length of the objective lens—and thus the instrument itself—longer. As Richard Panek writes in his book ...

When referring to the image above, biconvex and plano-convex lenses are considered positive ... known as the application's "best form" -- is key to minimizing optical distortion and aberration. Focal ...

Positive meniscus lenses have a shorter radius of curvature on the convex side and a longer radius of curvature on the concave side; the edges of these lenses are thicker than the center. A positive ...