EXPOSURE VALUE (EV) = ISO + Aperture + Shutter Speed
For photographers wanting to break away from their camera’s Automatic Settings, understanding exposure is the single most important concept to consistently take great photographs. Getting the correct exposure balances three primary settings on your camera; 1) ISO, 2) lens aperture, and 3) shutter speed. This series of topics explains ISO, Aperture, and Shutter Speed and the benefits, and trade-offs associated with adjustments.
When your camera is set to automatic mode you don’t have to think about adjusting these settings. But automatic does not always provide the results you want. Understanding the elements of exposure (and the trade-offs associated with these settings) can help you to get the most out of your camera.
QUICK OVERVIEW OF SETTINGS
1) ISO refers to how sensitive the camera sensor is to light. In the old film days, the combination of chemicals used to make the film could be adjusted to be more, or less sensitive to light (ranging from ISO 100 – 800). Many digital camera today reach beyond ISO 3200.
Typically, photographers set their ISO in advance of taking photos, based on the amount of available light. When bright lighting is available (outside, or studio) setting the ISO at 100 or 200 is suitable. For darker lighting situations (arenas, sunrise/sunset) a higher ISO is often necessary (e.g. 800 – 1600).
2) Aperture refers to the size of opening inside the lens that allows light to enter. The value is represented either as a ratio (e.g. 1:4.5) or as a focal length stop (e.g. f/4.5).
Aperture can sometimes be confusing to remember because a smaller aperture number (1:2.8) indicates a larger diameter opening to gather light, and a larger number (1:22) indicates a smaller diameter opening. But if you think of it in similar terms as Shutter Speed, a smaller number allow in more light, and a larger number allows in less light.
3) Shutter Speed is measured in fractions of a second, and refers to the length of time the camera shutter is open to allow light to make contact with the camera sensor (or camera film). Note that some cameras indicate this speed with a whole number instead of a fraction (e.g. 60 is 1/60th of a second). Most digital cameras indicate longer exposures (full seconds) with a ” after the number. For example, 30″ is a 30 second exposure.
The longer the shutter is open, the more time is available for visible light to make contact with the sensor. When there is not much visible light, the shutter needs to stay open longer for the image to be bright enough. On bright light days, the shutter needs to open and close extremely fast to avoid photographs from getting over-exposed.
BALANCE & TRADE-OFFS
Adjusting any of these three camera settings can influence the amount of light the camera sensor captures. As indicated in this illustration, changing any setting also influences image quality.
This graphic is a useful reference tool for remembering the benefits and trade-offs in balancing the three primary settings contributing to exposure.
Changing ISO from a lower to higher setting introduces “noise” into the image (in the film days this was referred to as “grain”). Changing the Shutter Speed from faster to slower intervals cannot stop motion, resulting in a blurry image. Changing the Aperture from closed-down (f/16) to wide open (f/2.8) limits the Depth of Field (DOF), which is the horizontal depth of the image that is in focus.
Photographers often want their photo to look a certain way; e.g. blurred background, stop action, low noise, etc. This can be difficult to achieve when you allow your camera to think for you. Understanding these settings will go a long way to improving your photography.
IN DEPTH: More Detail Here on: ISO | APERTURE | SHUTTER SPEED
The video takes a couple looks at the components of exposure.
[youtube https://www.youtube.com/watch?v=rQJjEmt5w98&w=420&h=315]