Do More With Your DSLR I: Working with Available Light
Recently, I found myself in a bit of a quandary. My fellow Vimeo Staff members and I were getting ready to shoot a new Vimeo original video, when it fell upon me to handle the camera and make sure it was set up for the lighting conditions we were shooting in. Oh no, what would I do? I was going to try the old press-some-buttons-and-hope-for-the-best technique, but luckily Lan and Vu, the Bui brothers, appeared and passed on some of their extensive DSLR knowledge. Here's how it all went down:
Now, I'm going to let you all in on a little secret: I was merely acting like a DSLR novice. As hard as it may be to believe, I actually do have a decent grasp on the topic of available light. However, for the sake of entertainment — and your education — I was willing to pretend otherwise. Let's dig into what the Bui brothers taught me:
Exposure, or the amount of light that the camera sensor receives, is dictated by a few factors, but one of the most critical is your f-stop. Your f-stop is a measure of aperture, or the diameter of opening that allows light to pass from the lens onto the camera's light sensor. Aperture is expressed as f-stop, and will be indicated on your camera in abbreviations that look like this: F2.8 or f/2.8. Here's a diagram that shows varying f-stops and the corresponding opening each represents:
The "F" stands for the focal length of your lens, and the number indicates the diameter of the iris opening. A smaller number like 1.8 or 2.4 means the diameter is greater and more light is reaching the sensor. You want to change your aperture to let in more or less light depending on the conditions you're shooting in.
Another important factor to keep in mind when considering aperture is depth of field. Depth of field refers to the part of the image that is in focus. A deep DOF allows both the foreground and background to appear in focus, while a shallow DOF will allow you to focus on a single area or subject. The amount of depth in your shot should be based on your subject matter. If you're shooting an establishing or landscape shot, you probably want to show most things in focus with a a deep depth of field. Conversely, if you're focusing on a person, you might want to blur your background to draw your audience's eye to what's important.
White balance is a calibration that enables your camera to show colors accurately under varying light conditions. Think of it as making sure the color white is always white so that your image doesn’t have unwanted tints. Many cameras come with automatic white balance, which works pretty well most of the time, but sometimes you'll want to adjust it yourself. You can do this a few different ways, the easiest of which is with presets. The most common presets are sunny, cloudy, fluorescent, and tungsten. These balance the image color based on those general lighting conditions. Some cameras will have more presets than others, so play around and test what happens when you change the presets.
Certain cameras will allow you to manually adjust the white balance. On a DSLR, this is usually done by adjusting the Kelvin color temperature. As the Bui brothers explain, every type of light has a different temperature. Warmer temperatures are orange, cooler temperatures are blue, and each temperature corresponds to a number value. Daylight is usually somewhere around 5500K. Number values above that correspond to cooler light, and numbers below that correspond to warmer light. If you know the temperature of the light you're in, adjust according to that. However, this can also be done by eye. Using the live view on your LCD screen, adjust the temperature until the whites are white, or until you get the temperature and look you desire.
On some cameras, you can set your white balance by taking a picture of a white object and calibrating the appropriate temperature that way. Once you do this, the camera will know this is the color of pure white in your lighting situation and adjust the image colors accordingly.
When shooting only with available light, as is common with documentaries and other types of on-the-fly shooting, you have to think about where your key light is. If you're shooting outside during the day, your key light will be the sun. It's generally good practice to try to shoot your subject so the key light is not directly behind them. Rather, you should move your camera so the light source shines on your subject's front-right or front-left side. A quick and easy way to enhance natural lighting is to use a bounce, which will give you lighting that is more flattering, with fewer harsh shadows.
The next element to consider is ISO. Paired with aperture, this is how you achieve the proper exposure when shooting on a DSLR (since your shutter speed should usually be set to twice your frame rate). On a film camera, ISO is a measure of film speed, or the film's sensitivity to light. On a digital camera, ISO measures the sensitivity of your camera's light sensor. On a DSLR, ISO usually ranges from around 100 to perhaps 6400. The higher the number, the more sensitive it is to light. In general, the darker your shooting conditions, the higher your ISO should be, and the brighter your shooting conditions, the lower your ISO needs to be.
You can also use ISO to compensate for stylistic aperture choices. For example, in this tutorial, the Bui brothers suggested I open up my aperture to blur the background behind my subject. To maintain the proper exposure, we needed to turn down the ISO. Alternately, if you need to shoot at a small aperture, you might need to turn up the ISO. Keep in mind, however, that the higher the ISO, the more noise, or graininess, your image will have.
Shooting in Low Light
When shooting in low light, you'll need to pull out all the stops. To let the maximum amount of light into the camera's sensor, open your aperture all the way and bump up your ISO. In the shot of Vimeo man dancing with the girl in the street, we chose a wide aperture of 2.8 and a high ISO of 5000.
That about sums up all the knowledge the Bui Brothers imparted upon me. Whether you know a little bit about DSLRs, or you're a complete novice like the Dan in the video, I hope this lesson will set you on the path to mastering your camera.