Lens jargon explained
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02-11-10, 01:41 AM
Join Date: Sep 2010
Firstly welcome to the forum. Okay, now to the Jargon. The "mm" ranges refers to the lens length. The lower the value, the wider the field of view. Wide angle lenses are used for landscapes or architecture and are generally 18mm and below. Conversely, the higher the number, the greater the magnification power of the lens, making distant objects enlarged. If they have two different "mm" lengths on them, it means the lens is a zoom lens. For example an 18-200mm lens, will zoom from landscape to telephoto. If a lens has only one "mm" length on it, like 50mm, it means it is a fixed focal length.
Also written on the lens is an "f" number. This refers to the aperture of the lens. The aperture acts like the iris in your eye and expands and contracts to control the amount of light entering the sensor. The wider the aperture, the more light is let in. The smaller the aperture, the less light reaches the sensor. The aperture also controls the depth of field and sharpness in a photo. When it is wide open, the depth of field is very shallow, which produces photographs where the backgrounds are nicely out of focus. When the aperture is stopped down to make it smaller, it increases the depth of field, making the background more in focus. It also makes the photo sharper. Its the same when you squint your eyes to make things clearer.
In general, the lower the "f" number, the more expensive the lens. For example a 70-200mm f/4.5-5.6 may cost you 200 pounds (sorry got no pound sign on this laptop). A 70-200mm f/2.8 may cost you 1500 pounds. The reason is that the f/2.8 lens lets in much more light than the f/4.5-5.6, which means you can use faster shutter speeds to get the same exposure. This can mean the difference between a picture having motion blur and not having motion blur.
The camera you linked to comes with two different lenses. One is 18-55mm, which will do wide angle landscape shots but also zoom for close portraits. If you put the camera up to your eye and the looked over it at someone at the 55mm length, they will roughly appear the same size in the camera, to the naked eye. The 55-250mm will zoom from close portrait length to telephoto. If there was a bird in a tree 20m away, you could zoom in on it to make it larger in the picture. Both lenses also have IS or image stabilization. This is a feature that compensates for the vibrations caused by holding the camera. It helps to eliminate motion blur.
Hope that helps. If you have any other questions just ask. Now I really must go to bed lol.
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