The magnification of 20x refers to the quantity of magnification. This zoom magnifies 20 times, so if you were photographing anything 20 feet away, it would seem to be 1 foot distant. A distance of 100 feet appears to be a distance of 5 feet. Optical zoom outperforms digital zoom. Optical zooms produce images with more detail and are less likely to distort shapes or colors.
When you zoom in far on a photo, objects appear smaller. When you zoom out far, they appear larger. If you double-tap the screen, the camera will automatically zoom in for you. This is known as optical zooming. Double-tapping again will let you optically zoom out once more.
You can also use pinch-to-zoom. With one hand on the screen and one hand covering the other side of the display, you can zoom in and out by pinching your fingers together or spreading them apart on the screen.
20x is quite a lot of magnification. At this magnification, small objects appear small and far away. Large objects appear large but still far away. You can see how far away something is by looking at it through the lens. Objects that are far away look small while objects that are close up look big. Things that are closer than what can be seen with the unaided eye appear magnified on your camera's display screen.
A 200mm lens on a 35mm frame is equivalent to a 4x "zoom" for your eyes. On the 20D with the 1.6 crop factor, 200mm corresponds to around a 6.4x "zoom" (200 x 1.6)/50. A 300mm lens would be 10x "zoom".
Because human perception is logarithmic, the difference between 2 and 3 images at 100% size is much greater than that between 5 and 8 images at 80%. This means that you can get away with more extreme zooms than you might think if you use large prints or otherwise expose carefully.
For example, a 500mm lens on a film camera has 12.5x optical magnification. At full resolution, this would require an image circle of about 40cm (15.5in) to contain all the information! Most commercial photos are taken at least partly off-center, so only part of the image circle is used and the effective magnification is reduced. With a 2:3 ratio photo, we could fit five of these images side by side in the same space as one long image from a 1000mm lens!
We also need to take account of the fact that the eye is relatively insensitive to detail beyond about 18-20 inches (45-50cm), so a very wide angle lens gives us a lot of room for cropping after the fact.
That's the full-zoomed-in version. So, for example, when we're fully zoomed in on the 12x, an item 50 feet away will get a 6 foot wide image. The more times you zoom in, the smaller the item and the further away it gets displayed.
It's important to note that while the camera has 12 times optical zoom, the actual zooming happens at the lens, not at the camera body. The lens can be extended beyond its normal range, allowing you to take pictures from far away.
Optical refers to the fact that the zoom mechanism uses lenses instead of motors or wires to change the distance between them. This type of zoom is found on most digital cameras these days. It's very common for manufacturers to claim 12x optical zoom even if all they mean is that they were able to create a system where the lens can be retracted all the way back while still being able to take pictures. Some lenses can reach up to 200x magnification!
In addition to optical zoom, many modern cameras also offer digital zoom, which involves projecting a small section of the overall image onto your screen during playback. This works by taking several photos simultaneously and combining them into one large image afterwards.
Consumer cameras are marketed with a maximum zoom, which is designed to indicate how much closer they are to the subject. For example, a camera may have a 40x zoom, a 4x optical zoom, and a 10x digital zoom. Could someone please clarify that in simple English? I think I got it but want to be sure.
When you push the button that sets the max zoom, the lens extends as far as it can, which is called "maxing out" the zoom. At this point, images that use all the pixels on the sensor will be the largest that can be made while still keeping focus within range of the autofocus system. Most cameras allow you to display a percentage value on the screen when zooming in using the digital zoom feature, so you know how much more you can zoom in before losing focus.
The number that appears on most cameras is the maximum resolution that can be recorded by the camera at its current setting. For example, if you were taking pictures at ISO 3200, which is a high sensitivity setting, then only those photos would be able to store detailed information about objects being photographed. A lower sensitivity setting would allow for larger prints or further away shots.
So, the answer to your question is that the maximum zoom on a consumer camera is designed to indicate how much closer they are to the subject.