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F-Stop and Aperture
We often see on a camera brochure that says "Lens: 35-105mm f-3.5-f8". The "f-3.5-f8" is called the F-stop or the maximum aperture of the lens. This figure is derived from dividing the focal length of the lens by the aperture opening of the lens.
The photography term we often see in photo magazine "opening up 1 F-stop," means making the aperture size larger to allow more light through the lens and "stopping down" means making the aperture size or F-stop smaller to allow less light through the lens. A larger aperture size is represented with smaller number hence f2.8 is larger f-stop than f5.6. The standardised F-stop number runs as follows : f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22, f32, f45, f64. Each number admits half the light to the previous F-stop. So in our example above the f2.8 allows about 8 times more light through than f8.
Lenses with a wide aperture such as f1.4 are more expensive than one that has an aperture size of f4. Manufacturers can often enhance the quality of a mediocre quality lens by limiting the aperture size of the lens in effect limiting the use of the centre portion of the lens. This is because the centre of a lens has less distortion to the light passing through it than at the fringe of a lens. So limiting the aperture to say f5.6 will improve a cheap lens considerably. Inexpensive 35mm cameras usually have maximum aperture size of f5.6 or f8!
Now you have learnt that the larger the aperture the more light can pass through thus enabling you to take pictures indoor or in poor lighting condition, so if you use your camera indoor most of the time you should look for cameras with an aperture of at least f2. However, if you are an outdoor person you can save some money by buying a camera with a f5.6 lens. It is a compromise and most medium price range cameras will have aperture somewhere between f2.8 to f4 and often the in between number of f3.5.
When choosing a zoom camera we can't do much on this aperture figure so choose as wide an aperture you can find for the wide-angle range and use the telephoto for outdoor scene. This variation of aperture can cause problem to flash light admitting incorrectly exposed pictures at certain zoom range which is sometimes experienced with inexpensive zoom compact cameras. For the better designed zoom compact camera manufacturers have overcome this problem by limiting the maximum aperture to a narrower range using special mechanical zoom linkage to the aperture and programming the electronic of the built-in flash light to include this short coming. Camera with Through The Lens(TTL) flash sensor is the best solution to this flash exposure problem with zoom lenses.
The problem we mentioned above is easily solved with digital cameras due to the small size of the image sensor or CCD, thus making a large aperture lens a lesser problem with digital cameras as compared to film cameras. You can find a digital camera with specifications that read
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