Focal length?

I heard a lot about two terms "focal length" and "wide angle" from many photographers and hobbyists. This was always a puzzle for me; finally decided to get into it of-course by googling :)

I came to know that focal length is a major factor to be considered before buying a new lens.

So here's how it goes:

When parallel rays of light strike a lens focused at infinity, they converge to a point called the focal point. The focal length of the lens is then defined as the distance from the middle of the lens to its focal point.




Normal, Wide-Angle, Telephoto, Zoom

We usually categorize lenses as having a wide-angle, normal or telephoto focal length. A normal 35mm lens covers a 24x36mm film with a field of view that corresponds approximately to our normal vision; a lens with a focal length of 50mm (55mm is also popular) is considered as normal. Any lens with a focal length less than 50mm (or 55mm) can be considered as wide-angle; any lens with a focal length greater than 50mm (or 55mm) can be considered as telephoto. A zoom lens offers a range of focal lengths. The table below lists some of the more popular focal lengths.

Lens	Focal Lengths (35mm cameras)
Wide-angle	18mm, 20mm, 28mm, 35mm
Normal	50mm, 55mm
Telephoto	90mm, 135mm, 200mm, 300mm

35mm Film

Do not confuse '35mm' lens with a focal length of 35mm. The former refers to traditional 35mm film camera format (also known as 135 format). In other words, '35mm film camera' refers to the 135 film format -- not the lens format. [35mm is the width of the film including the sprockets.]