In chapters point-n-shoot camera and D SLR camera we read about the focal length of lens which is measured in millimeters. On every zoom lens there is inscribed one number like 18-55mm, 100-300mm, 6-28mm or something else. This means that the lens can move itself from 18mm from the sensor to 55mm away rom the sensor. now in the market lenses available from 3X to 24X zoomin power. So how do we actually verify which lens has what amount of zoom?
Maximum Focal Length / Minimum Focal Length = X zoom power
Example: On the camera lens is inscribed: 18-55mm
55mm (Maximum Focal Length)/18mm (Minimum Focal Length) = 3X
IMP NOTE: A higher X value need not mean that it has more zoomin power. X in true sense tells us the range that the lens can cover. Lets see 2 examples: 6-60mm lens / 100-400mm lens.
Using the above formula we see that the 6-60mm lens has 10X zoom
100-400mm has 4X zoom. In general people tend to think that since 6-60mm lens has more 10X value so it has capability of capturing images of faraway objects. No its not true. To capture images of faraway objects you need more value in mm. 18mm less closeness--180mm more closeness-400mm very close and so on. So 6-60mm means a very good range that the camera can cover but it cannot reach out too close to a distant object. Where as 100-400mm has less range but is capable of bringing in close a faraway subject.