Lenses
Author: Goran Katić
Lenses are basic optical part of every camera. Main task of a lens is to take in and transfer wanted amount of light to the film.
Lens Characteristics
Focal Length is the distance between the middle of the lens and the sharply outlined image on focal plane, when the distance is set on infinite. Focal Length is marked with a letter “f”.
Lens Light Sensitivity – the stronger the light sensitivity is, the more light lens with a completely open aperture will take in. More light sensitive lens effectiveness comes up when shooting in low light conditions. The smaller the number is the better quality the lens has. That means the lens marked 1.4 has better quality then the one marked 2.8. Lens light sensitivity is marked with a capital letter “F”.
We differentiate three types of lenses according to their focal length:
1. Wide-angle – made for shooting wide frames (large groups, factories etc.) These are the lenses with a shorter focal length (15-40mm) and large view angle. On the 14mm – 114 degrees while on the 35mm – 64 degrees of view angle. As opposed to tele lenses, these have large dept of field, but also a fault which is a stronger curvature of lines in the corners of a photograph.
There is a difference between a fish-eye and a standard wide-angle lens. Fish-eye lenses are specific because their focal length is about 8mm and their view angle is as large as 180 degrees. They give a round image on the negative. That’s why the photograph taken with a fish-eye lens is extremely deformed. The closer you get to the object, the more deformed the object becomes. These lenses were primarily made for scientific purposes.
2. Normal – in analog photography, this is the most used lens. If you would purchase analog camera would always get a 50mm lens with it. These lenses have a 45 degrees wide view angle, which are a bit larger then the human view angle. They also have the best quality because they don’t have as many optical faults.
3. Tele Lenses – made to shoot objects which are hard to approach as well as for photographing portraits. Main characteristics are longer focal length, smaller view angle and small dept of field. Focal length of these lenses is from 70 – 135mm and even more.
For photographing portraits 70 – 135mm lenses are used, and for sports minimum 200 – 300. The longer the focal length lenses have (over 300), the longer and heavier, as well as clumsier, they are. These lenses need tripods and monopods because it’s almost impossible to get a stable photograph from hands e.g. 800mm Sigma lens has almost 5 kgs.
Special Lenses
1. 1. ZOOM-lenses – lenses with adjustable focal length. In the beginning photographers were not fond of them because of their low light sensitivity and many optical faults (soft image). Today, those faults are mainly eliminated and lenses like these are sold the most, because for a small price they offer everything a photo-amateur and/or a photographer needs. That is coverage of every angle of view – all in one lens. These lenses are used in a photo-journalism as well, because they decrease a need of changing lenses in important situations.
2. 2. Macro-lenses – their most common focal lengths are 50 and 105mm. Best macro-lenses are the ones with a fixed focal length and strong light sensitivity (2.8 or 1.8). Their characteristic is ability to capture an object from very close, e.g. Sigma 50/2.8 can focus on 2cm while a standard 50mm lens can only focus on 20cm.
Lens Accessories
Lens hoods – are set on the end of a lens to block direct light, which is falling on a lens, in order to prevent glare and unwanted lens flare. Lens hoods are also good when photographing on rain. When choosing lens hood it’s important for it to match the angle of view otherwise it will shadow the edges of photographs (if the angle of view is bigger). To be more exact, the photograph we take will have shadowed edges. In today’s lens catalogs it’s specifically pointed out which lens hood goes with which lens, this way you can hardly make a mistake.
Filters – photo filter is a colored plastic gelatin disk or a colored framed glass. This frame is set in front of the lens or the source of light. They are not only used for color and contrast correction but they are also a binding part of a lens protection. Filters protect lenses from dust and scratches. It’s easier to buy a new filter for $10-20 when it gets damaged, then buying a new lens for several hundered and thousands of dollars.
Teleconverter(s) – is an optical system set between the camera and the lens. It increases the focus length of the lens, however, it, also, decreases the light sensitivity of the same. There are converters with 2x and 3x factor. To a 50/1.4 lens, teleconverter will increase the focal length to 100mm but will, also, decrease the shutter aperture from 1.4 to 2.8. When a teleconverter decreases the shutter aperture from 1.4 to 5.6 it also increases the focal length to 150mm. This means that a 2x teleconverter decreases four times lens light sensitivity while a 3x teleconverter decreases eight times lens light sensitivity. Teleconverters are used on the lenses which have a better quality.
Table for easier lookout:
Using teleconverter 2x
Shutter Aperture f/ 1.4 2 2,8 4 5.6 8 11 16 22 32 New Shutter Aperture f/ 2.8 4 5,6 8 11 16 22 32 45 64 Using teleconverter 3x
Shutter Aperture f/ 1.4 2 2,8 4 5.6 8 11 16 22 32 New Shutter Aperture f/ 4 5,6 8 11 16 22 32 45 64 90
