Exposure Triangle for Beginners
Come around young ones. It’s time to master the magic photography ratio: the exposure triangle. The three variables, aperture, ISO, and shutter speed, allow you to manipulate the exposure of an image. In this blog, we explain what they are and how to balance them.
Aperture is expressed in f-stops. The wider the aperture (lower the f-stop) then the more light gets into the lens, whereas a smaller aperture (higher f-stop) translates to less light. You might think that a wider aperture is always best because it gives you the most light (and therefore the best image), but smaller apertures produce lower depth of fields. Hence, artsy bokeh shots require enough light to stop down your aperture without totally going dark.
ISO refers to light sensitivity, in that it alters the amount of light you can shoot with. Back in ye olde days of exclusively film cameras, ISO wasn’t adaptive. You chose your ISO sensitivity per roll of film. With digital, however, it’s a lot more flexible. You can manipulate sensitivity for each image individually. The lower the ISO number, the less sensitive your camera is to light. The higher the number, the more sensitive.
You can ratchet your ISO up to capture photographs in very low light, but the increased sensitivity comes at a price: “noise.” Noise refers to the added grain in pictures with high ISO taken in low light. However, ISO range is still useful when the aperture cannot physically open any wider to accommodate more light, or when the shutter cannot stay open any longer without sacrificing sharpness.
Shutter speed is arguably the most important aspect of the exposure triangle. Shutter speed refers to how long the shutter stays open, and therefore how long the sensor is exposed to light. The faster the shutter speed, the less time the senor has to collect light. Slow shutter speeds give the light more time to reach the sensor for a higher exposure. Quick shutter speeds create sharp images, while slower shutter speeds can generate artistic blur (or unwanted blur, as the case may be).
Yes, there’s math – but we’re not getting into the crazy details. Suffice to say: if you change one side of the exposure triangle, then you need to adjust the others. Opening the aperture without lowering ISO or shortening exposure time will create an overexposed image. Similarly, ratcheting up ISO without closing the aperture or shortening exposure produces similar ill effects. However, if you extend your exposure time with too small an aperture, you’re likely to get a blurry image.
Mastering the exposure triangle takes some learning, but keep at it. If one combination isn’t producing desired results, play around. When constraints rise up with one third of the triangle, you still have two more sides to work with.