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			How To Understand your Camera and Film 3: Lens Terms by David Barry Article Rating = 3.81 (41 votes)

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Category: Hobbies & Recreation : Photography LENS APERTURE / 'f-STOP' / 'f' NUMBER / LENS 'SPEED' The other way of controlling exposure of a film is with the lens aperture, often called 'f stops' or 'f numbers'. Inside a camera lens is a mechanism called a diaphragm, consisting of a set of rounded leaves or blades, which can be opened inwards or outwards. The blades form a rounded hole called the aperture. This is like the pupil in your eye, which expands or contracts when the light changes. So too can the aperture expand (to pass through more light and produce more exposure on the film) or contract (to pass less light, and produce less exposure on the film). The aperture controls the intensity of light on the film at a particular instant in time. The aperture settings - the size of the aperture - are indicated by 'f numbers' on a ring outside of the lens. 'F stops' or 'F numbers' are often in a sequence something like this: 1.4 2 2.8 4 5.6 8 11 16 22. . . etc Some of the end numbers may not be shown, depending on which brand and model lens it is. Again, these numbers are actually fractions (or ratios) of another number (which I will discuss later), but it's important to remember that the smaller the f number, the larger the aperture, and the larger the f number, the smaller the aperture. So at f 1.4 the aperture is larger than at f 5.6 which is a larger aperture than at f 16. Thus, at f 1.4 the aperture passes more light than at f 5.6 where the aperture passes more light than at f 16. Another thing to remember is that each of these consecutive f numbers produces half the exposure of the preceding f-number, or twice the exposure of the next f number, even though their numerical values is not changing by 2x. There is a mathematical reason for this which I won't explain here for the sake of simplicity. So the aperture at f 2.8 produces twice the exposure of the aperture at f 4, but half the exposure of f 2. Some older lenses may have slightly different numbers, but the same principle applies. Lens speed is the maximum aperture (or smallest f number) available on a lens. In the example above, the speed of this lens would be f 1.4. Lens speed is useful for comparing lenses of otherwise similar specifications. So, for example, a lens with a maximum aperture of f 1.4 is a faster lens than one with a maximum aperture of f 2.8, and may be more practical than the latter when photographing in situations of poor light. About the author... Submitted By David Barry Description Photo enthusiast Web Page not available Other Articles in this Category How To Understand Your Camera and Film 9: Filter Types by David Barry How to Understand Your Camera and Film 8: Using Filters by David Barry How To Understand your Camera and Film 2: Shutter Speed by David Barry How To Understand your Camera and Film 4: Putting it all together by David Barry How To Understand your Camera and Film 1: Film Speed by David Barry How To Understand Your Camera and Film 6: Lens Focal Length by David Barry How To Understand Your Camera and Film 5: Film Types by David Barry How to Understand Your Camera and Film 7: Depth of Field by David Barry Other Sites Storkin.com - Baby and Pregnancy Tips and Discussion iPhone Games at TouchArcade.com iPhone Apps at AppShopper.com Health Articles Menopause Symptoms HIV/AIDS Symptoms West Nile Symptoms Diabetes Symptoms Pregnancy Symptoms Read other Articles - click here.