The Basics

The way we see objects in an image is dependent on the distance it is removed from us and the type of lens used. If a subject is captured with a 50mm lens (35mm equivalent) we experience a more natural perspective than if it is captured with a wide-angle or tele lens. With a 50mm lens or at a standard zoom setting we can guess the difference between objects according to our real life experience.

Since tele lenses have shallow depth of field even at smaller apertures, the background may be blurry ( which can be effectively used to separate subjects from their background) but it seems to be relatively close. In this case we speak of "flat" perspective, .

Pitfalls

Due to the way different lenses or zoom settings affect perspective, it pays to know what focal length to use for certain subjects.
In landscape photography for instance the idea mostly is to show a lot of the scene in front of you. This would best be captured with a wide-angle lens since this is able to show the wide open space before you. Because wide-angles open up perspective, some foreground interest will be necessary to avoid creating an "empty" photograph.

For the same reason a wide-angle should not be used for close-up portraits, as the facial features of a person will be distorted beyond recognition. If you definitely want to use a wide-angle to show a person in its surroundings, make sure he or she is not situated directly in the foreground or at the extreme borders of your image, as this is where perspective distortion will manifest itself most strongly. Keep the person away from the extremes of your image and a natural looking portrait will be the result.
When using long tele lenses be aware that with distant subjects, haze and mist can affect the apparent sharpness of an image. A skylight filter will lessen this effect, or shoot early in the morning before the sun has warmed the ground. Take great care when focusing with a long tele as depth of field will be very shallow. A long telephoto at maximum aperture and focused on a subject 5 meters away will only give a few inches depth of field.

Depth of Field

Depth of field (DOF) refers to what is and isn't sharp in a picture. Images with great depth of field have a large zone of sharpness, so that everything from just a few feet in front of the camera to infinity will be sharp. Depth of field at a given focusing distance extends 1/3 in front of the point of focus and 2/3 behind it. The three key factors to depth of field are aperture, lens type or focal length and subject distance:

Aperture
By closing the aperture, you are not only limiting the amount of light that reaches the CCD but you also create a greater area of sharp focus. The smaller the aperture you choose (say 16 or 22) the larger the depth of field.

Lens type
At any given aperture, a wide-angle lens or the wide-angle setting of a zoom lens yields far more depth of field than telephotos or tele settings. A 28-mm lens set to f8 gives a larger area of sharpness than a 300-mm lens at the same aperture.

Subject distance
The closer your subject is to the camera the less depth of field you get for any given lens type or aperture. This is the reason there is so little depth of field in macro photography where the subject is often only inches away from your camera.

Macro Mode

Normally the term macrophotography refers to images in which the subject is presented at a ratio greater than 1 to 1, so bigger than lifesize. It could be compared to looking at a subject through a magnifying glass. On a digicam however, macro mode refers to the possibility to get very close, though not strictly on a 1 to 1 ratio, although some cameras can get extremely close to a subject while others merely use the zoom function to magnify it and fill the frame.

There are a few things to consider if you want to achieve really good macro shots. For a start, focusing will be very critical as at such close distances depth of field will only be a few millimeters. Therefore subject and camera should be parallel to eachother and a small aperture should be used. As a consequence, shutter speeds will be quite slow, so arrange for some kind of support like a tripod or some other stable platform.
To minimize camerashake, it is best to use a cable release or the self-timer as well.
Using the in-camera flash should be avoided. Its light is usually too harsh and will cause overexposure. It is much better to use some form of natural lighting. A north facing window on a cloudy day will yield very even soft lighting, while a piece of white cardboard can lighten the shadows or provide soft lighting by acting as a fill-in reflector.

Optical Zoom

The optical zoom is a true zoom which uses the whole of the CCD unlike digital zoom, which is a mere crop of the central part of the CCD, making up the image of the central pixels of the CCD only.

Zoom lenses on digicams usually range from 35 to 70mm, which is sometimes called a standard zoom, or they may be anything between 28 and 135mm or more, which gives you much more versatility and a much wider range of coverage.

One of the best things about a zoom lens is that you can actually change your angle of view without having to move about much. This can be convenient when you don't have space to move backwards and still want to capture the whole of a scene. or when you want to react quickly to photo opportunities and want to zoom in on the action to isolate it from its surroundings.

Telephoto Lenses

By tele lenses we mean anything with a longer focal length than 50mm. They range from short teles of about 70mm to very long ones of more than 500mm, which are used for capturing action at major sporting events or wildlife shots.
With a telephoto lens you can crop in tightly on the subject, to capture detail or isolate it from its surroundings which makes for compositions with lots of impact.

As opposed to wide-angles which open up perspective, tele lenses compress space, making subjects in a scene appear closer together than they actually are.
When using a telephoto it is especially important to hold it steady, as the effect of camera-shake will be magnified as the lens gets longer. A useful guide would be to use a shutter speed equal to the focal length of the lens or one stop faster to be on the safe side.

Wide Lenses

By wide-angle lenses we mean anything with a shorter focal length than 50 mm.
They range from ultra wide-angles of about 17mm to a more conventional 35mm. The latter is probably the most common focal length found on digicams. Its angle of view
is 63 degrees, which makes it convenient for general photography.