W means "Wide Angle" and
T means "Telephoto", then how does optical and digital zoom relate? Does W and T fulfill both zooming options?
It depends on your camera. The W and T are simply directions. It's a bit like left and right. W is for wide and means it will make the field of view (how much area the picture covers) wider (zooming out) and T is for tight, which makes the field of view smaller (zooming in).
Some cameras will have this control handle both optical and digital (cropping) zooming. Normally these cameras will use the optical zoom first as it maintains the overall resolution of the image. After the limit of the optical zoom is reached, the camera may start cropping the image (a digital "zoom"), which makes the field of view narrower but is really just discarding portions of the image you don't care about for you.
Other cameras (though more rarely) have a specific digital zoom setting that you can set a crop factor and then the zoom controls just work with the optical zoom. This is helpful for making sure you don't accidentally discard part of the image or go beyond the meaningful optical zoom.
Some cameras also have an option to limit the amount of digital zoom that it will apply (or even disable digital zoom altogether, which is a good idea if you intend to do post production work on the images as it lets you crop after the fact rather than while shooting.)
Optical zoom means that the optics — the lens configuration — actually changes. From an idealized math point of view this is the same as cropping to the center of an image and enlarging. Of course, in the real world, there are significant disadvantages (chiefly, loss of resolution), but for practical purposes digital zoom can be used to seamlessly extend the range of actual optical zoom.
So, in most cameras that I've seen with this feature, you do indeed use the
T controls. When you exceed the actual focal length of the lens by pressing
T for a while, the camera will switch to cropping the center and expanding to fill the LCD screen (there may be a warning or indicator, or there may not be). When you pull back in to a wide angle with
W, you'll switch back to optical zoom. But the key thing is: Does W and T fulfill both zooming options? Yes.
"Zoom" means the ability of a lens to change its focal length (from W to T in your nomenclature). (see also What is focal length and how does it affect my photos?)
"Optical zoom" is a real, physical change of the lens geometry, while the so-called "digital zoom" is only cropping and enlarging a part of the digital image - which you can do as well or better after shooting, with any image editor program.
(The advantage of doing it yourself would be that you can choose which part you want to crop, not only the center.)
W - wide angle of view T - telephoto = narrow angle of view
This has nothing in common with difference between optical zoom and digital zoom.
Optical zoom changes the actual focal length of the lens. it doesn't affect the resolution at all but it may affect the speed of the lens (ammount of light reaching the sensor).
Digital zoom, on the other hand, is just cropping the image. Nothing more. It does reduce the resolution but it doesn't touch the lens in any way.
T = Telephoto W = Wide-angle Your camera features a zoom lens that you control via a manually rotatable knob or leaver. This grants you the ability to adjust the optical power of your camera lens. As you dial this control towards “T”, the lens mechanism increases the optical power of the lens into the region of telephoto. As you move this control towards “W”, you are entering the realm of wide-angle. What is happening, the individual lens elements reposition as well as the distance lens to sensor. This results in a variations in the focal length (power) of the lens.
Focal length changes by zooming)is a relatively modern scheme. Years ago our gadget bag was jam-packed with wide-angle, telephoto and normal focal length lenses. Zoom lenses are generally comprised when we compare image quality, zoom vs. fixed focal length (prime lenses). The difference in quality are shrinking thanks to modern technology.
Disregarding quality differences, cameras with enormous zoom range sell better. To deliver such super ranges, camera makers supplement the limits of their optical zoom range via an electronic zoom. The idea is to add oodles of zoom in hopes of oodles of sales. Nowadays electronic zoom is OK and getting better. What you need to know is, the electronic zoom method does not add detail to the vista as you zoom. What is happing is, the digital image is being enlarged by spacing out the pixels. This technique greatly enlarges (crops) the center portion of the recorded image. What do you think happens when the pixels (picture elements) are stretched? The data in the pixels between is fabricated. In other words the spaces between the pixels with real data are chock-full of made-up data.
Don’t get me wrong, the software of electronic zoom compares data in the adjacent pixels and guesstimates the contents of the now interpolated pixels. In most cases the resulting enlarged image created by the electronic zoom method will be acceptable. However, think about aerial reconnaissance. Would you bet your life on interpolated gun emplacements? Electron zoom need not be confined to the camera. Most all image editing software will enlarge this way.