In part two of the ‘Lens types explained’ serie we will take a closer look at plano convex and plano concave lenses. We will also discuss biconvex lenses and biconcave lenses.
Plano convex lens
As you may have read in the first blog of this series a convex lens is a lens that has at least one surface that curves outward. A convex lens can converge and focus a light beam. A plano convex lens is a convex lens with one flat side and one curved side, as can be seen in the image below:
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Plano concave lens
The concave lens is thinner at the center than at the edges. Light rays that pass through a concave lens are diverged, as such this type of lens is good for light projection or beam expansion. The plano concave lens has one flat side and one side that is curved inwards, with a negative focal lenght.
A lens that has two surfaces that curve outward we call a biconvex lens, or double convex lens. When both surfaces have the same radius of curvature, the lens is equiconvex.
You can best use a biconvex lens when the incident and outgoing beams are mirror images of one another. E.g. the beam incident on the lens is diverging, while the beam leaving the lens is converging symmetrically.
A lens that has both surfaces curving inward we call a biconcave lens. Biconcave lenses, also known as double concave lenses, are also used for beam expansion, light projection and image reduction. The lenses can expand the focal length of an optical system. Biconcave lenses have two negative focal lengths.
A lens that has one surface that is convex and the other that is concave we call a convex-concave, or convex-meniscus. These kinds of lenses are mostly used for corrective lenses.
All lens types
Below are images that clearly shows the different lens types, ranging from plano convex lens to concave meniscus.
Read part 1 of the ‘Lens types explained’ blog.