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Wednesday, June 5, 2013

Photography: Chapter 5

About lenses

Well, you can easily guess that the most critical piece of photographic equipment other than the camera itself is the lens. Since lenses can be passed on from one camera to the next and are a huge factor in the overall quality of the image, therefore, most photographers spend a lot of money to purchase high quality lenses

Let’s start with what role the lens plays in the photography. 

Camera uses the lens for many tasks such as focusing on a subject, metering a scene, delivering and focusing the light onto the camera sensor. The lens also decides the amount of the scene that will be captured (the frame).

Lenses are composed of optical glass that is both concave and convex in shape. By definition, a lens in context of photography is an optical lens or assembly of lenses used in conjunction with a camera body to focus the light coming in from the front of the lens onto the photgraphic film/ sensor. The amount of light that enters the camera is also controlled by the lens, the size of the glass elements, and the aperture mechanism within the lens housing. Most lenses these days include things like the autofocus motor and, in some cases, an image-stabilization mechanism also

While in principle a simple convex lens will suffice, in practice a compound lens made up of a number of optical lens elements is required to correct (as much as possible) the many optical aberrations that arise

Let’s understand what optical aberration is and how it can impact the image

Optical aberrations occur when points in the image do not translate back onto single points after passing through the lens. This can cause image blurring, reduced contrast or misalignment of colours. Optical aberrations are present to some degree with any lens. This is a very critical parameter that determines the cost of the lens

Lenses are typically divided into three or four groups depending on the field of view they deliver

Wide-angle lenses cover a field of view from around 110 degrees to about 60 degrees. Wide-angle lens allows more of the scene to be included in the photograph and is very useful in situations where the photographer may not be able to move farther from the scene to photograph it; such as architectural, interior and landscape. For a full-frame 35 mm camera, a lens of focal length 35 mm or less is considered a wide-angle lens. An ultra-wide-angle lens is a lens whose focal length is shorter than the short side of film or sensor. For 35 mm film or full-frame sensor any lens shorter than 24 mm

A normal lens has a field of view that is about 45 degrees and delivers approximately the same view as the human eye. A normal lens will have a focal length between 35 and 80mm. Normal focal-length lenses are useful for photographing people and for most other general photographic needs

Telephoto lens is a lens in which the physical length of the lens is shorter than the focal length. They can range in length from 135mm up to 800mm or longer and have a field of view that is about 35 degrees or smaller. Telephoto lenses are ideal when you can’t get close to your subject e.g. in a sports arena or in a bird sanctuary, since they have the ability to greatly magnify the scene, allowing you to capture details of distant objects. Pictures taken on telephoto lens tend to look 'flat', and a bit more two-dimensional

"Close-up" or macro lens are used for extreme close-up photography, usually of very small subjects, in which the size of the subject in the photograph is greater than life size. The ratio of the subject size on the sensor plane to the actual subject size is known as the reproduction ratio. A macro lens is a lens capable of reproduction ratios greater than 1:1

And based on focal length flexibility there are two kinds

Prime lens is a fixed-focal-length, or uni-focal lens. Zoom lens on the other hand has a variable focal length. Prime lens is less versatile than a zoom in terms of focal length range but is often of superior optical quality, wider maximum aperture, lighter weight, smaller size or lower cost. A prime lens has fewer moving parts, fewer optical and a less complicated lens formula. Therefore, they suffer from fewer problems related to optical aberration. Because of simple optics, prime lenses usually have a larger maximum aperture which allows photography in lower light and a shallower depth of field

50mm f1.8 prime lens are quite popular; renowned for delivering quality in a nominal budget
If your camera is with a crop sensor, 50mm is a perfect length for head and shoulder portraits
Wider aperture of prime lens offers small depth of field; hence ability to isolate subjects from the background i.e. more creativity
Prime lenses generally offer sharper, crisper shots than a zoom lens and the only downside that I see with a prime lens is that your feet become your zoom. But I believe that can make you a better photographer. Not being able to zoom your lens to get the shot, you need to think, you need to get creative

Zoom lens on the other hand is a one box solution; variety of focal lengths in one package. This means that if you want to shoot different focal lengths on a day, you do not have to carry around a bag full of lenses. So, prime or zoom? Answer depends on what you shoot. Subjects in fast moving environments need zoom. For portrait work, I will advise to go for prime

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