As a simple description; a lens is the thing that gathers light coming from the scene and project the light onto the film or CCD Sensor (in digital cameras). There are four basic types of lenses and main difference of these types is the their angle of view.

Normal (Standard) Lenses

Angle of view of this lens group is very similar to human eye (45-50 degrees) this is why they are called “normal” or “standard” lenses. An important advantage of these lenses is, not decomposing the image like wide angle lenses and fisheye lenses does.Normal Lenses are light, relatively cheap and their quality is remarkable because of these most of the photographers have one of them.

Wide Angle Lenses

The focal length of wide angle lenses are shorter than 50mm and they are able to see the angles that you can not see with your one eye. Using both of our eyes we see about 75 degrees angle. A 28mm lens’ sees the same angle with us approximately 75 degrees which means lenses with shorter focal length than 28mm can view wider areas than us even we are using both of our eyes. Focal length of wide range lenses varies generally from 35 mm to 6mm, angle of view increases as the focal length decreases.

Their biggest advantage is letting you capture most of the scene. They are mostly used for landscape photography and for capturing the widest shot at narrow places (such as capturing the whole group of people in a small room). Also you can create unusual effects on your picture with them, such as exaggerated perspective which is like an optical illusion that makes the close objects look bigger than normal and the far objects smaller than normal perspective, that way the distance between them looks greater than usual. The picture below is an example for exaggerated perspective;

But as angle gets bigger deformation level at the edges of picture increases, vertical and horizontal lines in the picture start to loose their straightness’ and look like curves. The picture below is an example for deformation caused by wide angle lenses;

Tele Lenses (Narrow Angle Lenses)

Lenses which have longer focal length than 60mm are called “Tele Lenses”. These lenses lets us shoot the distant subjects that we can not get close such as wild animals and sports events. Their angle of view is narrower than human eye. Short tele lenses (60 - 85 mm) are good for shooting portraits from a distance without closing to the model too much which makes our model feel more comfortable. Long tele lenses are better for sports events and wild-life photography.

Zoom Lenses

In modern photography zoom lenses are very popular, and the main reason of their popularity is their ability to change their focal length and do the job of several lenses. If you have 28-200 mm zoom lens, you can use it for any type of photography and any condition or having three lenses will be enough for a normal photographer such as 17 - 35 mm , 28 - 70 mm , 80 - 200 mm.

Other Types

Fish - Eye Lenses : Extremely wide angle lenses like 6 mm

Macro : Can focus at minimum distances, genrally used for photographing bugs or flowers to be able to capture the most tiny details.