Understanding the ‘zoom’ specs thrown at you when looking at cameras and lenses is not especially difficult hard, but it is important so you know you’re comparing apples with apples.
Zoom basically refers to the angle of view of an image. Optical zoom is achieved by elements of the lens moving to increase the magnification sent through to the image sensor in your camera. Alternatively, digital zoom is achieved by simply cropping the image after it’s received by the sensor. There’s no lens movement and therefore results in significant image quality loss.
This loss is always the case with photo cameras. It’s essentially been the case with video cameras in the past as well, although things have changed slightly over the past few years. As video cameras are equipped with higher resolution sensors, it allows them to reduce the physical area on the sensor where they take the frame from, while still maintaining full resolution. It isntisn’t – still not ideal but it’s much more viable than before.
While we’re here, it’s also important to understand the relationship between zoom and focal length (or effective focal length at least). You’ll see ‘35mm equivalent’ on most spec sheets as this is the standard we measure focal length by. We need a standard because different sensor sizes need vastly different ‘real life’ focal lengths to produce the same field of view.
Focal length is the distance from the camera sensor to the optical centre of the lens. The longer the focal length, the narrower the field of view and the shorter the focal length, the wider the field of view. For example, 50mm is generally considered a ‘normal’ angle of view – similar to what our eyes see. Anything shorter is ‘wide angle’ and anything longer is ‘telephoto’.
Let’s bring it back to zoom. My tip is to always check the equivalent focal length range, because 10x zoom might not always be the most helpful measurement to go off by – especially if you need a very wide angle lens. Example: 24-240mm has a 10 times zoom factor (24 x 10 = 240), but so does 40-400mm, however there’s a big difference between 240 and 400mm, and certainly between 24 and 40mm!
Remember: optical zoom = good, digital zoom = less good/bad; short focal lengths like 24mm have a wide field of view and long focal lengths like 100mm have a narrow field of view.