Different Focal Lens Ranges

- My camera (the A570) has focal lens range 35-140mm eqv. and it is said to be 4x zoom.
- Compared to the S3 with 12x zoom with range 36-432mm eqv.
- Mounting the kit lens on the EOS 405D (the kit lens is the EF-S 18-55 mm IS), the equivalent focal lens range will be 28.8-88mm.

Note 1: Eqv. focal lens is the focal lens on a 36mm sensor sized camera (full frame camera like EOS-1Ds) that result in the same photographic angle like the real focal lens. The ratio between the sensor size and the full sensor size is called form factor. For example all Rebel series (300D, 400D, 450D, 1000D) has the form factor of 1.6 (i.e. its sensor size needs to be enlarged by 1.6 to become a full frame (36mm) sensor. Hence when the 18-55 lens is mounted on the 450D, the eqv range will be 18*1.6-55*1.6 which wil be 28.8-88

Note 2: 36mm eqv focal length is the standard photographing angle, focal lens below is consedered wide angles and focal lens above is considered telephoto (or zoomed in). So if you are moving from a P&S camera to dSLR and want to know what lens to give you the same result as your old P&S, don't just calculate the x zoom ratio of the lens (for example the 18-55 lens is a 3x lens). Instead, calculate the widest range to 36mm and the longest range to 36mm (for exampe the 18-55 when mounted on a 450D, will have the longest range of 88. This is equivilant to your P&S zoomed to only 2.4x).