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Jargon Buster

Jargon Buster

Need a little help with some of the following topics? Then read on...

Megapixels
Lenses and Optical Zoom
Focusing
Exposure
Storage, File Formats and Transfer

How Dotty do you need to be? Some facts about pixels

Digital cameras capture their images on a light sensitive chip inside the camera. There are two types of chip known as CCD and CMOS. CCD stands for charge-coupled device and CMOS stands for complementary metal-oxide semiconductor. They are often referred to simply as sensors.

The digital image captured on the sensor consists of lots of square (or sometimes hexagonal) dots known as pixels. One million pixels is called a megapixel. The resolution of the sensor is measured in megapixels, so you might have, for example, a 3-megapixel camera or a 7-megapixel camera.

The more megapixels your camera can record, the sharper the image will be. This is because more megapixels means smaller dots which blend better. If you don't have enough megapixels and/or you print very large photos then curves can start looking a bit jagged.

So how many megapixels do you actually need? Well a few years ago some cameras had less than 1 megapixel and 3 megapixels was considered relatively high. Nowadays 3 megapixels are found on entry-level cameras and most self-respecting point and shoot models have between 5 and 7 megapixels.

The fact is that unless you want to print very large images or do a lot of cropping to your pictures after you've taken them, you probably don't need as many megapixels as you might think.

A 3-megapixel camera will produce good 8x10 inch photos. Kodak claim a possible print size of 20x30 inches for a 4-megapixel camera. If you just want to print snapshots then anything which is 3-megapixels or above is going to meet your requirements.

Through the Lens - The Eye of Your Camera

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 so common on digital cameras these days that this is practicably 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.

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 so far back that you fall in the water or whatever.

Telephoto lenses have long focal lengths. A camera with high zoom will give you a longer focal length so you can zoom in on distant objects.

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.

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 image to select the correct focus.

Muti-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.

Hologram Laser AF is Sony's laser-assisted autofocus.

Cameras with Manual Focus put you firmly in the driving seat so this is something to consider if you want better focusing control.

Exposing the Truth - Getting the right amount of light into your pictures

In photographic terms exposure refers to the amount of light that reaches the film or digital sensor. In the good old days of film photography it was incredibly disappointing to collect your photos from Boots and find that all the outdoor shots were whitewashed and the indoor ones looked like they had been shot down a mine. In the first instance the problem was over-exposure and in the second it was under-exposure.

Film cameras control exposure by enlarging or decreasing the size of the aperture (measured in f-stops) and by having a faster or slower shutter speed. Both of these features have an effect on the amount of light that reaches the film. Digital cameras may also have the same features, or they may simulate these features by making the sensor more or less sensitive to light. But in any case, manufacturers still talk in terms of apertures and shutter speeds even if they mean the equivalent thereof.

The other factor that affected exposure in a film camera was the sensitivity of the film or its ISO rating. Film with a high ISO rating was more sensitive to light and could cope with very fast shutter speeds, but could produce a grainier image. Obviously a roll of film would have a set ISO rating and you wouldn't be able to change it between shots. Manufacturers also talk about ISO ratings when referring to the sensitivity of the sensor in a digital camera. With a digital camera you can change the ISO setting for each shot if this feature is available to you.

Depending on the sophistication of a digital camera you might find some or all of the following exposure features:

Programmed Auto Exposure
This is the fully automatic option where the camera chooses the aperture and shutter speed for you. You won't even have to think about it.

Aperture Priority Auto Exposure
In a camera with this feature the user sets the aperture and the camera chooses the shutter speed. This is good for variations in light conditions.

Shutter Priority Auto Exposure
This is the opposite of Aperture Priority, so you set the shutter speed and the camera chooses the aperture. This a good for fast moving objects.

Manual Exposure
This option, found on higher end cameras, lets you choose both the aperture and the shutter speed.

PASM
This stands for Programmed, Aperture, Shutter, Manual, so a camera with PASM does the lot.

EV Compensation (Exposure Value Compensation)
This is a feature that will let you override the camera settings to lighten or darken your image.

Exposure Bracketing
This feature causes the camera to take a series of differently exposed shots with one press of the button. With any luck one of the shots will be perfectly exposed. Or you can take the darkest and lightest image and combine them using photo editing software to get an image with both shadow depth and highlights.

Scene Modes
Scene modes are so common on digital cameras that they are almost de rigueur nowadays. They usually have names like "Snow", "Portrait", and "Sport". They are really just automatic aperture and shutter settings that are designed to give optimum results in tricky lighting condtions (like bright ski slopes) or when taking action shots (like racing cars.) Some cameras have a huge number of scene modes, like about 25, so there shouldn't be a lighting situation that the manufacturer hasn't thought of.

Storage, File Formats and Transfer

The move from film to digital photography has brought with it a whole new lexicon of words and acronyms associated with the storage and transfer of digital images. Here are some of the words and acronymns explained.

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