March 28th, 2015
This will be the first post in a series discussing exposure. Exposure, the amount and quality of light entering the camera, is measured (in the photography world) in "stops". An additional "stop" of light represents two times the amount of light present. Exposure is a function of three aspects. The exposure triangle (photo credit at link), as it is called, is determined by aperture, shutter speed, and ISO.
Aperture is the wideness of the lens opening, and available apertures change between lenses. Denoted by "f/x" nomenclature, smaller numbers denote wider apertures. For instance, f/2.8 is wider than f/4.0, which is wider than f/5.6. Lenses can have maximum (widest) apertures anywhere between f/1.0 to f/5.6 or so, and minimum (narrowest) apertures between f/22 and f/32. Wider apertures allow in more light than narrower apertures.
Shutter speed is the period over which the exposure occurs. When the shutter is actuated, it opens for a time relative to the shutter speed selected. Modern DSLRs have minimum shutter speeds around 1/8000th of a second, and have unlimited maximum shutter speed. Longer (slower) shutter speeds allow more light than shorter (faster) ones.
ISO is the camera sensor's sensitivity setting. With film cameras, ISO is determined by the film used. ISO values range from 50-102,400 in the 5D Mark III, and values vary widely between cameras. Digital camera sensors can become very sensitive to light, allowing narrower apertures, faster shutter speeds, or both to be used. Higher ISO values allow more light than lower ones.
Next time, we will begin discussing aperture, shutter speed, and ISO individually. We will look at the appropriate times to use different values for these, and how they affect the resulting image.
Any questions about exposure? Ask me directly using the contact form above, or do so in the comments.
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Hope to see you back next time!