dslr sensor crop and effective lens focal

[binaryknight]

could some one please expain this to me im aware the full sensor isnt used to take the picture but im in need of understanding how this effects the focal range of a lens.
ie after looking at lenses even though some are digital the lens is say 70 - 300 but the seller will state effective range on a dslr is 105 - 450 (numbers not exact but approx)

 

[AdWright]

Depends on the camera

Non-full frame Nikons - multiply by 1.5

Non-full frame Canons - multiply by 1.6

Lenses (even digital only, ie designed for smaller sensors) are always quoted with the 35mm (ie full frame) equivalent focal length

 

[xolotl]

Just to get a technical thing out of the way.

The focal length does not change. It is a physical property that doesn't change with the body.

What changes is the field of view. As most people were used to using 35mm is FOV is quoted in relation ship to a 35mm SLR.

For example 10mm on a 1.6X is equivalent to a 16mm FoV lens on a full frame sensor.

 

[Johnny|lucidcomposure]

could some one please expain this to me im aware the full sensor isnt used to take the picture but im in need of understanding how this effects the focal range of a lens.
ie after looking at lenses even though some are digital the lens is say 70 - 300 but the seller will state effective range on a dslr is 105 - 450 (numbers not exact but approx)

Consult this easy to use calculator for focal crops on various sensor sizes.

http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm