The lens is a major part of the camera arrangement comprising an optical element which serves to capture the image in front of the camera so that it can be accepted by the sensor or film. In compact cameras and prosumer cameras, the lens is made into the camera body, but the lenses used in SLR cameras sold separately. Both lenses are fused with a special lens camera or SLR cameras, both have similarities in working principle, optical design and characteristics.
High quality lens has the ability to deliver satisfactory results in terms of sharpness, contrast and color. To assess the performance of the lens makers can use MTF charts describing the quality of the lens. Thanks to modern lens manufacturing technology with the help of computers, today more and more quality lens and is equipped with modern features such as a special coating that can improve the sharpness and reduce flare. In choosing a good lens, the necessary basic understanding will be terms which are common to the lens, as well as recognize the division or classification by type lens.
Focal Length (Focal Length)
In discussing about the lens, the first thing seen of a lens is the focal length of the lens. By definition, the focal length indicates how the distance between the sensor (or film) of the lens, while the camera focuses to infinity (infinity). To show the focal length of this lens is used millimeters (mm). In a more general understanding, lens focal length indicates how much the corners of the image (picture angle or the angle of view) that can be produced by a lens. Corner of the image is what will determine the extent of the image area can be obtained at a particular focal length. Note:
- - Short Focal lens (eg 28mm) produces a great picture angle so as to obtain a wide image area or width (wide-angle). The shorter the focal then the vast area of the image that can be produced. Then the 18mm lens can be called more 'wide' than 28mm.
- - Focal length lens (eg 200mm) resulted in a small corner of the image so as to obtain a narrow area of the image, suitable for long distance photos (telephoto). The longer the focal, the more distant telephoto capabilities possessed the lens. So a 400mm lens can be called more 'tele' of a 200mm lens.
The lens focal length is considered equal to the area of the image seen by the human eye (angle picture about 46 °) is 50mm, so the lens with a 50mm focal commonly referred to as a normal lens. Focal lens with a smaller than 50mm wide lens called, objects are photographed with a wide lens result will look much further than the reality. Lens with a focal greater than 50mm is called a telephoto lens, the object photographed with a telephoto lens results will appear closer than it should.
So based on the focal length, at least we know the three types of lenses are lenses wide, normal and telephoto lenses. Wide lens suitable to get a photo with the widespread impression, such as scenery or architecture. While the telephoto lens is suitable for photographing distant objects such as when outdoor or sporting events covering the event. Normal lens itself is more suitable for facial portrait or other needs that require a normal picture angle.
Fix Lens and Zoom Lens
When viewed from the focal design, the lens can be classified into two main groups. The first is a fixed lens / prime (have a fixed focal length) and the second is a zoom lens / vario (have a focal length that can be changed).
Fixed lens has a small size, with a bit of an optical element and as the name implies, only fixed lens has a fixed focal length. Primes are available for a wide range of focal lengths ranging as:
- - Fix wideangle lens (24mm, 35mm)
- - Normal fixed lens (50mm, 60mm)
- - Fix telephoto lens (85mm, 105mm)
The zoom lens itself has advantages over fixed lens that has a focal range that can be changed, from the shortest focal to the longest focal. Ability is measured by comparing the zoom lens focal longest to shortest focal, eg, a 28-280mm zoom lens, the focal length is 28mm shortest and longest focal is 280mm, so the lens is called with a 10x zoom lens (or 280 divided by 28). The zoom lens has advantages in terms of practicality because the lens can be obtained with a wide variety of focal lenses for a variety of photographic needs and desired perspective. But in terms of sharpness, the zoom lens is not able to match the fixed lens. This is due to the complexity of the optical arrangement of the zoom lens so that potentially reduce the sharpness in general. In the zoom lens, the focal sharpness longest and shortest focal generally decreased.
Lens opening (aperture)
In the camera lens there is a mechanical component called the aperture or diaphragm, which serves to adjust the amount of light entering the lens. The diaphragm is composed of a set of thin metal layer (blade) that form a circle and the iris aperture size can be enlarged or made smaller. Setting the entry of light is done by changing the size of the aperture of the largest to the smallest openings in units of f-number. Large openings expressed in a small f-number, and vice versa small openings expressed in a large f-number. Lens with a large aperture has the ability to incorporate more light making it possible to use a higher shutter speed.
The picture above is the shape of the diaphragm of the lens, where the picture on the left shows the small openings and the right shows the large openings.
Large aperture (eg f / 1.4 or f / 1.8) is more easily realized in the fixed lens design. Then the majority of the fixed lens has a large aperture which also had the privilege to create an alias blur out-of-focus in the background. But not so with the zoom lens, in which to make a zoom lens with a large aperture a bit more difficult to do. In the zoom lens, maximum aperture common is f / 2.8, although there are now beginning to be found pocket camera has a lens that can open very big to f / 1.8.
Judging from its aperture design, the zoom lens itself is divided into two groups:
- - Constant aperture zoom lens
- - Variable aperture zoom lens
With a constant aperture zoom lens, for example, lens 24-70mm f / 2.8 or lens 70-200mm f / 4 maximum aperture lens indicates that this at any focal position is fixed. So for example the lens 24-70mm f / 2.8 will be able to open at f / 2.8 at 24mm to 70mm focal position. Such lenses are more difficult to make, also have a larger size and weight, so the lens of this type belong to the class of the zoom lens is expensive.
Variable aperture zoom lens with an easier and cheaper to produce, and has a smaller size so compact and lightweight. This type of lens has a maximum aperture that will shrink when the zoom lens at the shortest focal position to the longest focal. To determine the maximum aperture lens of this kind can be seen from the information that is written on the lens, such as lens 18-105mm f / 3.5-5.6 means this lens has a maximum aperture of f / 3.5 at 18mm focal position and maximum aperture will shrink up to f / 5.6 at 105mm focal position. Although not written in the lens, minimum aperture can actually shrink when the zoom lens. It depends on the design of the lens, the lens usually has a minimum aperture can shrink when the zoom lens is a lens SLR camera.
Due to the large aperture of a lens can incorporate more light making it possible to use a higher shutter speed, then the lens with large openings called with a fast lens. For a fixed lens, because generally large maximum aperture, then almost all primes called fast lenses. However, since it is difficult to make a zoom lens with a large aperture, the aperture zoom lens with constant f / 2.8 already can be called with a fast lens. Most SLR camera zoom lens which has a small size is a slow lens because it has small openings and will become smaller when the zoom lens.
Features Image Stabilizer
Some modern lens has now been equipped with image stabilizer feature that serves to dampen vibrations that occur when we take pictures. This feature adds an element lens special function to compensate for hand-shake is detected by the sensor, so that the risk can be reduced image blur. Own stabilizer function is required when the camera is used to take photos at a low shutter speeds or when using a telephoto lens.
When concluded, the classification of the lens can be arranged by:
Focal length:
* Wide Lens
* Normal Lens
* Telephoto lens
Lens Type:
* Lens fix / prime (fixed focal)
* Zoom lens / vario are subdivided into:
- Constant aperture zoom lens
- Variable aperture zoom lens
Design aperture lens:
* Fast lens (have large openings)
* Lens slow (have small openings)
Aside from the general classification as above, there are special lenses that are used for specific purposes, such as:
* Fish-eye lens for extreme picture angle (180 °)
* Macro lens for photographing objects very close (magnification 1: 1)
* Tilt and Shift lens for professional needs (control perspective)
