Lens mm

[Yochanan]

At the risk of sounding like a complete idiot, I will admit that I am have no idea what the millimeter numbers means on a lens. Is the larger number more zoom? How does it relate to optical zoom? :confused:

[Rhys]

The millimeters is the effective distance between the rear element of the lens and the film (or digital sensor). On modern lenses this distance is effective not actual. On older lenses it is an actual distance.

The more millimeters the narrower the angle of view from the lens and therefore the greater the effective magnification.

As an example, a 17mm lens is wide angle and a 200mm lens is not (this is called a telephoto lens).

A zoom lens is a lens that can vary its focal length (the number of millimeters). Common lenses would be 18-50, 70-300, 28-70 etc. On many compacts and camcorders the zoom is not given as a number in millimeters but as a ratio 1x, 5x, 40x etc.

[David Metsky]

To add to the above, 50mm is generally the same as viewing with the naked eye. It's not wide angle, it's not telephoto. Numbers greater then 50mm are considered telephoto, numbers less then 50mm are wide angle.

[Beowulff]

This is an interesting (and non-technical) page about lens geometry in general:

Understanding Camera Lenses (http://www.cambridgeincolour.com/tutorials/camera-lenses.htm)

Cheers :)

[Yochanan]

Thank you for all the help. :D

[TenD]

The millimeters is the effective distance between the rear element of the lens and the film (or digital sensor).


The focal length of a lens is defined as the distance in mm from the optical center of the lens to the focal point, which is located on the sensor or film if the subject (at infinity) is "in focus". The camera lens projects part of the scene onto the film or sensor.