Nearly all cameras today have an optical zoom lens. On a compact all in one camera the zoom level varies depending on the model in question, from entry level models with 3 x or 5 x zooms to a whopping 65 x of some bridge cameras. And Digital Zooms extend the range of your camera even more. However, using your camera's zoom is not as simple as just zooming into an image, there are several factors to consider to ensure you get the best possible picture. It may be better to crop an image rather than zoom in and loose quality. Read on to find the in's and out's of zooming to get the best photo's possible.

There's two numbers on a lens in milimetres, the lower is the wide angle and the larger is the Telephoto or high end of the lens. If you divide the telephoto length by the wide angle length, you get the zoom range. The lower the wide angle number is, the wider the lens is, meaning a wider area is captured by the lens. A 24mm wide angle lens will capture a wider image than a 28mm wide angle lense. My bridge camera has a telephoto length of  405mm and a wide angle of 27mm. 405 divided by 27 is 15 which is a 15 x zoom.The actual amount of zoom is known as the length that the image was taken at, for example 100mm or 84 mm. 28 mm(wide angle) is digital equivalent of 35mm on a compact film camera due to the sensor not using all the pixels of the sensor.

The more you zoom into a scene, the more image quality (usually sharpness) diminishes. It's not so obvious on a 3 x optical zoom lense, but on a 10 x zoom model or higher, it's much more noticeable at full zoom. This is due to two factors, camera shake, and a reduced aperature size.

At a longer zoom, the focal length narrows the aperature size, meaning less light enters the camera, increasing noise and darkening the overall image. On a bright sunny day the available light helps to avoid this. Also, zooming in increases camera shake adding blur to the picture. If the digital zoom has kicked in, it's magnified even more. You might have noticed that if you use your camera's full digital zoom, the image on screen is moving violently, and that's before the photo's been taken.

This shake can be avoided by using a tripod, as pressing the shutter button worsens the blur. Ensure the camera is screwed onto the tripod as tightly as posible, and the tripod legs are firmly secured, and its standing on solid ground. To avoid movement from pressing the shutter, set the camera's timer to the 2 second position if it has one. Most recent models do, but some older ones only have a 10 second mode. If your's doesn't, then use the camera's burst mode to take 2 or 3 shots in rapid succession. If the first image is blurred, the others should be sharp. This way, even shots taken with full digital zoom should come out sharp if the autofocus locks in the 'Green' position. 

The image above was taken with my 14 MP Bridge camera at full 15 x optical zoom. There is virtually no loss of sharpness because I used a tripod on a 2 second timer. The image below was taken at full 15 x optical zoom with a further 2.5 x digital zoom (total 37.5 x zoom) and although there's no blur, it's noticeably softer with a lot of digital noise due to the digital zoom being used.

At full 15 x optical and 5.7 x digital zoom (85.5 x total zoom) the image on the left is showing quite visible signs of soft edge bluring and severe noise. Note the red 'Ghosting' around the edges. Because a tripod was used the image retains a degree of sharpness. If it was taken hand held, the camera shake would have been too severe to use. The softness is due to the extra pixels added to a cropped image. The more you digitally zoom in the more the image is cropped, and the sensor adds 'Extra' pixels to take it back to it's original size. Extra noise and artefacts are a common problem with digital zoom. Some digital zooms work differetly giving a better end result, and are found on high end cameras. If you look at the image on the left, the darker areas appear blotchier because it's harder for the camera to guess what shade of pixel to add to the image.

Zooming into an image optically narrows the aperature size, reducing the amount of light hitting the camera sensor. If you only use half the opitcal zoom range on a 3 x zoom in bright sunlight you won't notice much difference in the overall image brightness, but if you're using a 15 x zoom at almost full zoom in low indoor lighting conditions you'll notice the difference. This is why the long zoom lenses on DSLR's are so large, they need a wide lens to allow enough light in to hit the sensor If your camera has aperature and shutter modes, just increase the aperature to allow more light in and increase the shutter speed to compensate for camera shake.

More expensive digital cameras have an F-stop number on screen. to aid picture taking. This is the relationship of the aperature size in relation to the focal length of the lense, and different lenses will have the same F-stop number for different lengths. F 8.0 on a 10 x zoom camera will be a different length in mm to F8.0 on  30 x zoom lens. The lower the number, the wider the aperature is, and more of the lens is used. The higher the number the smaller aperature and the smaller the area of lens used. The centre of the lense is usually sharper than the edges and if shooting conditions are bright enough a large F-stop number (smaller aperature) will give a sharper overall image. Entry level point 'n' shoot users don't need to be bothered about F-stops, though experienced bridge camera users will find them useful, especially for creating a striking depth of field..

This article has covered the basics of zoom lenses to enable you to understand how a zoom lens works and to help you use this to take better shots.