Photography Basics - Introduction To Lenses And Focusing

By Author: Adam Coupe
Total Articles: 18
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Introduction to lenses and focusing
One of the most important things in any camera, whether it's a digital model or a traditional film camera, is the lens. The lens is your camera's "eye" and it captures the scene. Professional photographers don't have whopping great lenses on their cameras for nothing. Good photographs depend on light and the lens is the point through which all the light must pass.
The job of the lens is to focus the image onto the sensor. Some very cheap cameras have a lens with a fixed focal length but most reputable cameras will have lenses with optical zoom. Optical zoom means that you can vary the focal length of the lens and the result of this is that you can fit in a wider landscape or zoom in on a distant object.
Focal lengths on digital cameras are, in reality, much shorter than they would be on traditional film cameras. However, manufacturers always give the focal length in terms of its traditional 35mm equivalent. So when a manufacturer says that a digital camera has a 3x optical zoom equivalent to a focal length of 35-105mm, they mean that the camera delivers the same zoom capabilities ...
... as a film camera with those measurements. Note that 35 multiplied by 3 is 105, so that's where the 3x figure comes from.
3x optical zoom lenses are som common on digital cameras these days that this is practically the minimum zoom ratio you would expect to find. Some better point and shoot models have 4x or 5x optical zoom. Cameras which are designed to be high zoom can have up to 10x or 12x optical zoom.
Be aware that digital zoom is not the same as optical zoom. Optical zoom uses the power of the lens to zoom in and out so you can choose how much of a scene you want to photograph. Digital zoom is really an on-camera cropping technique that takes the centre part of the image and enlarges it. This results in fewer and larger pixels and a degradation of image quality. If your camera has a very high pixel count then cropping the image in this way might not cause a problem, but it is something to be aware of.
Wide-angle lenses are those with short focal lengths. This might be in the region of 28mm or below. A wide-angle lens allows you to capture wider images without moving back so far.
Telephoto lenses have long focal legths. A camera with high zoom will give you a longer focal length so you can zoom in on distant objects.
Focusing More Clearly
A camera with Auto Focus will automatically focus on the subject to be photographed. Half pressing the shutter release button will usually focus the image before you take the picture. Continuous autofocus is a system that works even before the shutter release button is pressed.
Multi-point focusing is an autofocus system that uses several points in the points in the image to select the correct focusing point.
Multi-zone focusing is an autofocus system that automatically selects the zone (centre, left, right, upper, lower) on which to focus.
Cameras with Focus Assist use an infrared light to illuminate the subject so that the autofocus system can operate in low light.
Cameras with Manual Focus put you firmly in the driving seat so this is something to consider if you want complete focusing control.
This overview has hopefully helped to explain the basics around the tricky topic of exposure on modern digital cameras - other photography articles are available as a series.
Adam Coupe is pro commercial photographer specialising in commercial photography and architectural photography for a wide range of organisations that need to project their products, people or brand in a vibrant way see http://www.adamcoupe.com and http://www.adamcoupe.com/portfolio/category/19/architectural_photography/projects.htm