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04-25-2012 08:55 PM #1Junior Member Array
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- Jan 2012
The exposure triangle : ISO, Aperture and Shutter speed
In this article I will explain the exposure triangle. This consists of three photography principles that are essential for successful photographs. These are ISO, Aperture and Shutterspeed, as I will explain below.
An aperture is a hole, in this case a hole in the lens, that allows light to pass through. Using aperture priority (Aperture Value in Canon cameras) or manual mode, you can change the aperture to suit your subject.
A wide (larger) aperture allows more light in, while a narrow aperture permits less light to pass.
The size of an aperture is conveyed in f stops, or f numbers. Confusingly, the larger the f stop, the smaller the hole, and vice versa. For example, f2.8 is a wide aperture, and is usually considered most lens's widest aperture. On the other hand, f22 is a narrow aperure, and can be the smallest in some lenses.
So, a large aperture, has a smaller f stop. It also permits a faster shutter speed as I will explain presently. Camera sensors need a set amount of light to take a picture. So, a small hole lets less light in within a certain space of time than a large aperture would in the same timeframe.
Depth of field is a term that describes the area of an image that is acceptable sharp. A wide aperture has a shallower depth of field, because the shutter speed will be faster, so the camera has less time to take its surroundings in. The opposite applies to a narrow aperture, with it resulting in a deeper depth of field.
The main points of aperture are:
Large aperture = more light = faster shutterspeed = shallower depth of field
Narrower aperture = less light = slower shutterspeed = deeper depth of field
ISO is part of the exposure, playing a part in light sensitivity. On traditional film SLRs, ISO was called film speed and was determined by the film used. Digital cameras have a feature that allows us to change the ISO to alter light sensitivity. The higher the ISO, the more light sensitive the sensor.
Despite this, shooting on the highest possible ISO is not advised, due to noise. Aperture has a side effect (depth of field), as does ISO, but ISO is in no way desirable. It is grain, or colour blotches that adorn the image, and sap detail.
Thanks to this, it is advised that you shoot at the lowest ISO for your shooting situation.
This is the most self-explanatory of the two. It is the length of time for which the shutter curtain is open for.
It is measured in seconds and milliseconds. A fast speed (1/1000 is faster than 1/500) appears to freeze the motion, while a slow speed blurs, and accentuates it.
In this case, the side effect is blur. It can be derived from camera shake (unwanted) and long exposures (slow shutter speeds (desired)). This is classically seen in ''silk water'' waterfalls.
Shutterspeeds generally range from 30 seconds to 1/4000, also with bulb (shutter remains open for as long as shutter button is pressed down. Bulb is usually used for photographing fireworks, or astrophotography.