Getting The Light Right – understanding exposure
All photography – even documentary photography – is art. The way you compose your shot, the settings you choose and how you interact with your subject can completely change your image, and through your image the story you tell. This post builds on the introduction to help you get to grips with balancing aperture, shutter speed and ISO in your photography.
Exposure, aperture and shutter speed
Leave your ISO at the same level and increase the aperture, and you’ll have to reduce the shutter speed to expose your photograph well. This is because a larger aperture (smaller f-stop) lets more light fall on the sensor which means you need to have the shutter open for a shorter time to compensate. Similarly, if your shutter is open for a longer time you need a smaller aperture. A longer shutter speed means light falls on the sensor for more time, so you need to reduce the hole through which the light enters the camera or your image will be overexposed (too light). Because you can balance things out, you can use the shutter speed and aperture in different ways and still get a well exposed photo. This enables you to tell the story you choose by selecting the settings that give the image you want.
Through intelligent use of composition, aperture, ISO and shutter speed, you can direct the viewer’s attention, indicate relative importance of different aspects of the image, change moods, indicate relative speeds and imply togetherness or isolation. These are just a few of the effects well thought-through use of camera settings can effect, and every photographer will create something different. I would never use a camera’s bland defaults, but if you must, do so as a result of an informed decision and not because you know nothing else. It’s not as hard as it sounds. Play with the camera and settings for long enough and all this will become second nature.
Getting Around Lens Constraints by changing the ISO
Different lenses (and some compact-style cameras) have different maximum and minimum apertures, so you might not be able to get the effect you want by using just shutter speed and aperture. If you’ve decided on the story you want to tell and therefore know what aperture and shutter speed you want, but your camera shows the shot as overexposed or underexposed, you need to change your ISO. You make the sensor less light sensitive by dialling the ISO down, and more light sensitive by making your ISO higher. For example, maybe you want to show some motion blur on a very bright day. You are already using a dark filter and even with your lens’s smallest aperture (the biggest f number) the light meter shows your image is too bright. Make your ISO lower (and the sensor less light sensitive) until the combination of aperture and ISO compensate and your light meter shows your desired exposure.
Getting the hang of the relationship between shutter speed, aperture and ISO
If you are still unsure of how aperture, shutter speed and ISO work together, spend some time with Eleanor’s visualiser to get used to the relationship between shutter speed, aperture and ISO. Start by playing with either the shutter speed or the aperture and you’ll see that bigger apertures (smaller f-stops) or longer shutter speeds will make the central image very light. This is overexposure. Small apertures and short shutter speeds do the reverse, making the central image very dark and this is underexposure. Once you’ve got the hang of balancing these, start playing with ISO as well. It won’t take long before you get a feel for how the settings work together. Then put your camera on manual and try it in as many environments as you can. Don’t play with shutter or aperture priority yet as I’ll cover them later.
All you need
The principals covered in this post and the one before are really all you need to be able to take really good photos. Get your fingers accustomed to making the changes, learn how to do so through the lens (or by setting up the shot without using the menus with Live View if your camera has no through the lens options) and the rest is window dressing.
Every Wednesday I post something that will help my students. Each blog post is the synthesis of my experience as a pro-phtoographer and years of teaching photography to adults, children and teenagers. To attend a group course find me at City Academy or for flexible one-to-one tuition and portfolio building contact me directly.
this post, like all posts, is my exclusive copyright.