In my last post of “Explain Optical And Digital Zoom” I used the 4x optical zoom as an example of comparing digital zoom to optical zoom.

What Does 4x Optical Zoom Mean? To truly understand the magnifying power of optical lenses, you have to know another terminology: Focal length.

In simplicity, focal length is the length from the optical lens to the image sensor of your digital camera. See the illustration below:

The optical zoom is changed by changing the focal length. The longer the focal length, the more zooming effect is has, for example, the more zoomed in the image will be. The focal length is usually specified in mm (millimeter) in the digital camera realm.

Take a look at the illustration below. The focal length has been increased in the optical lens of the camera, therefore the image taken by the camera will be more “zoomed in.”

So, What Does 4x Optical Zoom Mean? Specifically what does 4x mean?

4x optical zoom simply means that highest focal length is 4 times the lowest focal lenth. For example, a lens that specifies 100mm - 400mm focal length would be a 4x optical zoom (highest focal length of 400mm divide by lowest focal length of 100mm gives 4), same as another lens that specifies 18mm - 72mm. What people don’t realize is that the focal length is the determining factor of how much you can zoom in. Remember, the higher focal length zooms into the subject more. Just study the above two illustrations and you can see why that is. The lower figure shows that the lens is farther away from the image sensor. It has a larger focal length than the above illustration, therefore capturing a smaller field of view, but it “zooms in” on the subject and project that image into the image sensor.

When you just talk about 4x optical zoom, you are only talking about how capable the lens can zoom into its lowest focal length. There are different lens types available for most digital SLRs. Some of which you may have heard of such as macro, telephoto, and super telephoto lens. If you want to capture something far away, you may want to try a telephoto or super telephoto lens that has a focal length range of 100mm to 800mm. Therefore, if you have a telephoto lens of focal length 600mm - 1200mm, you can really zoom in the details of your subject taken, even though it is only a 2x optical zoom (1200mm divide by 600mm).