Lens

Chapter  Fourteen

A photography lens (also known as objective lens or photography objective ) is an optical lens or assembly of lens used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.

While in principle a simple convex lens suffice, in practice a compound lens made up of a number of optical lens elements are required to correct (as much as possible)  the many optical aberrations that arise. Some aberrations will be present in any lens system. It is the job of the lens designer to balance these out and produce a design that is suitable for photographic use and possibly mass production.

There is no major difference in principle between a lens used for a camera, a telescope, a microscope, or other apparatus, but the detailed design and construction are different. A lens may be  permanently fixed to a camera, or it may be interchangeable with lenses of different focal lengths, apertures, and other properties.

Camera Lenses are manufactured in three categories in terms of coating. These coating on lenses is made with Magnesium Fluoride

1 Non Coated Lens

2 Mono Coated Lens

2 Multi Coated Lens 

Types of simple lenses

Lenses are classified by the curvature of the two optical surfaces. A lens is biconvex (or double convex, or just convex) if both surfaces are convex. If both surfaces have the same radius of curvature, the lens is equiconvex. A lens with two concave surfaces is biconcave (or just concave). If one of the surfaces is flat, the lens is plano-convex or plano-concave depending on the curvature of the other surface. A lens with one convex and one concave side is convex-concave or meniscus, It is this type of lens is most commonly used corrective lenses.

 

If the lens is biconvex or plano-convex, a collimated or parallel beam of light traveling parallel to the lens axis and passing through the lens will be converged(or focused) to a spot on the axis, at a certain distance behind the lens (known as the focal length). In this case, the lens is called a positive or converging lens.

Positive converging lens

 

If the lens is biconcave or plano-concave, a collimated beam of light passing through the lens is diverged (spread); the lens is thus called a negative or diverging lens. The beam after passing through the lens appears to be emanating from a particular point on the axis in front of the lens; the distance from this point to the lens is also known as the focal length, although it is negative with respect to the focal length of a converging lens.

Negative diverging lens

Convex concave (meniscus) lenses can be either positive or negative, depending on the relative curvatures of the two surfaces. A negative meniscus lens has a steeper concave surface and will be thinner at the center that at the periphery. Conversely, a positive meniscus lens has a steeper and will be thicker at the center than at the periphery. An ideal thin lens with two surfaces of equal curvature would have zero optical power, meaning that it would neither converge nor diverge light. All real lenses have a nonzero thickness, however, which affects the optical power. To obtain exactly zero optical power, a meniscus lens must have slightly unequal curvature to account for the effect of the lens thickness.

Next Chapter is about Types of Camera Lens. If you have any question regarding Photography just feel free to ask. So stay with us and like us on facebook.