What is lens?
A Photographic Lens is an assembly of lens which helps camera to record image. A lens may be permanently attached to camera or interchangeable. Lenses are available in different focal length, aperture and other features. It is worth understanding the basics of lens in order to have creative control over our photography techniques.
Construction of lens
The photographic lens was invented keeping, the human eye in mind. The lens sees an image, focus it, and then transmit its color, sharpness, brightness to the sensor just like eyes transmits it to our brain. A camera lens is made out of glass or plastic. A series of lens elements in different groups bends or reflects the light to meet or converge on a single point.
Lens elements are generally described by shape.
The element of photographic lens contains convex, biconvex, plano-convex glasses. There are also concave glasses, biconcave, and plano-concave glasses. The elements are not necessarily symmetrical and can curve more on one side than the other. At the middle of the lens there is thickening with relation to its edges causes light rays to converge or focus. Photographic lenses with thick edges and thin at the middles make light rays disperse. A complex camera lens contains a many number of elements which are specially grouped. There are combination of the composition, shape and grouping of the elements which maximizes the light-bending properties of the individual elements to produce the desired image. Focusing a photographic lens is done by moving it near or father from the focal plane.
Focal length & Viewing angle
The focal length of a lens defines the lens’s angular field of view. The shorter the focal length, the wider the angular field of the lens. The longer the focal length, the narrower the angular field of the lens. Additionally, the shorter the focal length of the lens, the shorter the distance needed to obtain the same FOV compared to a longer focal length lens.The focal length is used as a reference point according to a 35mm sensor camera. This is because the effective focal length and angle of view changes according to the size of the sensor. The APS-C sensor is smaller than a 35mm full frame sensor. So, to calculate the actual focal length of a APS-C sensor you have to multiply the original focal length with multiplying factor. The factor with Nikon APS-C sensor camera is roughly around 1.5 and Canon is around 1.5. This means the sensor size of Canon APS-C camera is slightly smaller than Nikon’s APS-C.
Since the focal length determines the viewing angle, it is worth looking at the viewing angle at a different focal length.
Standard Lens – A standard lens is a prime lens which has a similar angle of view to the human eye. This is exactly the reason why pictures taken with standard lens looks natural to the viewer. It sits between wide angle and telephoto lens. The viewing angle of human eye is around 46˚ so is the case with a 50mm lens. Since there are no zooming in or zooming out process involved in making a 50mm lens, it is the most economical to make hence less priced.
Fixed Focal length lens – A fixed focus lens is a lens where the focal length cannot be changed. These are also called prime lens. Just because the focal length cannot be altered, it is comparatively easier to make and often light weight. The most popular fixed focal length lens among the photographer is 50mm. Other focal length such as 20mm, 35mm, 85mm, 105mm, 200mm etc. are also available in the market.
Zoom lens – The popular category of lens which has a variable focal length. It comprises of an assembly of lens elements and groups that allows the range of focal length. From wide to telephoto, one can compose image in different focal length without physically moving. A zoom lens can do work of multiple prime lens in terms of focal length. Like a 18-55 lens will have a range between 18mm to 55mm.
Wide–A photographic lens with focal length below 50mm is considered as wide angle lens.
Telephoto – A photographic lens with focal length above 50mm is considered as telephoto lens.
Fisheye Lens – It’s a specialized lens. It’s a wide angle lens which provides extremely wide angle of view, at times up to 180˚.
Macro/Micro Lens – This lens is used for close up photography. The short minimum focusing distance enables this lens to go closer to the subject and focus. These lenses enable you to obtain life-size or larger images of subjects like wasps, butterflies, and flowers.
Tilt-Shift Lens – This lens is used when u need to shoot buildings. This photographic lens enables us to manipulate the vanishing points. This helps in the perspective of an image so the parallel lines don’t converge, thus eliminating the distorting quality of the lens. It also enables us to selectively focus an image; where only specific portions of the image are in focus and out of focus within the same plane.
Aperture is the opening of a lens’s diaphragm through which light passes to the sensor. Size of the aperture is controlled either manually or by programming done inside the camera. The size is controlled by diaphragm.
Auto focus lens
An autofocus lens or AF lens which can focus automatically with the help of focusing system available in the camera. Majority of the lens manufactured today has autofocus as well as manual focus options. Although autofocus works perfectly fine in most of the situation, we need to focus manually particularly when camera can’t see things properly.
Manual focus lens
Very few lens these days has only manual focus mode. These photographic lenses are not capable of focusing automatically. One example of such lens is Tilt Shift lens. To minimize the cost of production there are manufactures who are making prime lenses which don’t have autofocus capability.
Vibration Reduction (VR) or Image stabilization (IS) is a technique that stabilizes image from the shaky effect of hand holding. It lets, you shoot without any shaky effect with a relatively slower shutter speed. The lens uses a motion sensor to detect the motion of the camera shake and automatically corrects it. This is a useful feature to have in a photographic lens.