All cameras have a lens. There are compact cameras known as point-and-shoot cameras which have built-in lenses and they cannot be changed. On the other hand there are dSLRs which gives the flexibility to change the lens. Hence dSLRs cost more and you have to purchase one or more lenses. Lenses involve many complicated terms such as 18-55mm, zoom lens, telephoto lens, fisheye, macro lenses and many more.
In the good old days the cameras came with a normal lens – 50mm. These lenses were strong and rough but provided high quality shots. However these lenses provided low quality zoom and had other problems.
Today’s lenses are much more sophisticated and are power-packed with great features. However, there are many technical terms involved in understanding lens. Once understood, the lenses can help you add more creativity as well as control to underwater photography.
One of the most important concepts of lenses is the focal length. Focal length is usually expressed in millimeters but in older lens it might be in centimeters or inches. Focal length is generally in terms of optical system and is a measure of the strength of lens as to how it converges or diverges light.
Wide angle lenses usually have small focal length as small as 10mm or 20mm. smaller the number, wider is the lens. On the other hand telephoto lenses have a larger focal length such as 200mm or 300mm. Zoom lenses can zoom in and zoom out. Suppose a zoom lens says 20mm-100mm.the smaller number 20mm is always first and represents the widest focal length of the lens whereas the larger number 100mm represents the focal length while zooming in. Here you can see 20mm is five times 100mm, therefore this is called as 5 X zoom.
Lenses which have large maximum aperture are typically much heavier, larger and hence they will be more expensive.