Focal length / Multiplication factor

Focal length and viewing angle

The focal length is a number in milimeters (mm) which indicates how many degrees the lens is able to cover.

Focal length and length of the lens are not the same.  Some shorter lenses have more focal length than other longer lenses. 

Table

Focal length            Viewing angle

15mm	180 º
20mm	94 º
28mm	75 º
35mm	63 º
50mm	46 º
85mm	28.5 º
135mm	18 º
200mm	12 º
300mm	8.25 º
400mm	6.16 º
600mm	4.25 º

Graphic

Multiplication factor

The data on the lenses regarding the focal length are given for a sensor of 35 mm in size, but just some professional cameras have that size, the rest have smaller sensor size.

To know what focal length corresponds to our camera we need to know the mutiplication factor of that camera. The smaller the sensor size the greater the number of factor.

We have to see that number in the instructions for the camera and multiply that number by the focal length of our lenses. 

Examples

Canon 60D - factor 1.60x - lens 50mm

A lens with a focal length of 50mm on that camera corresponds to:

50 x 1.60 = 80mm

Canon 7D - factor 1x - lens 50mm

The lens does not change, a focal length of 50mm on that camera correspond to:

50 x 1 = 50mm.

Camera with a lens factor 1.50x - lens 70mm

70 x 1.50 = 105mm.

So if we put in that camera a 70mm lens it will be actually acting like a 105mm by the multiplier effect.

Extenders

With them we can increase the focal length of the lens. There are different values.