Focal length and its importance.

Definition.

When light rays pass through a lens, focused at infinity, the focal length is the distance, measured in millimeters, from the middle of the lens to where the rays of light converge to a single point.

The point where the light rays converge is the focal point.

This is a very simple diagram and explanation of this term.

Camera lenses are made up of several lenses grouped together, which make things a bit more complicated.

It will however do for our purposes of understanding the basics.

Lenses.

The three groups of lenses we will be discussing are.

1. Wide angle lenses
2. Standard lenses
3. Telephoto lenses

Wide-angle lenses have a length of less than 50 mm.

With these lenses the objects in the scene are smaller than with a standard or telephoto lens. There is however more of the surrounding area included in the scene.

These short lenses also produce a greater depth of field.

A standard lens is one with a length of 50 or 55 mm.

These lenses see the scene before them close to the same way the human eye will see it.

The third group contains the telephoto lenses. These are lenses with a length of greater than 55 mm.

Telephoto lenses will include less of the surrounding subject matter in the scene, however the objects included will be larger than with the wide-angle or standard lens.

Telephoto lenses will also produce a shallower DOF.

To summarize.

This is a basic introduction to focal length. What it is and how it relates to taking pictures.

You now understand whether a lens is wide-angle, standard or telephoto depending on its length.

You should also be able to choose the correct lens for the type of shot you wish to take.

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