Tutorial: Setting Exposure on iPhones, DSLRs, and Camcorders
All camcorders have automatic exposure modes that you can use for interviews, meetings, performances, and the like. However, auto-exposure doesn’t always give you the best result, particularly under challenging lighting conditions. While auto-exposure certainly has its place, for most meetings and talking-head shoots, you’ll get a better result if you manually control exposure.
In this article, I’ll discuss how to “go manual” with a professional camcorder and DSLR. This means how to set shutter speed, gain, aperture for the camcorder, and shutter speed, aperture, and ISO for the DSLR. In both cases, your guiding light will be zebra stripes, so I’ll describe what they are, how they work, and how you can use them to achieve accurate exposure.
Zebra stripes are the stripes you see on my forehead in Figure 1 (below). They tell me that the lighting is optimal for my face. Scattered around the LCD are the configuration options I set to achieve this lighting, with the 1/60 of a second on the lower left being the shutter speed, 0dB on the extreme right the gain, and F3.4 on middle bottom stripe the iris setting or aperture. These settings created an image that is crisp and clear, and that will look better after the encoding and transcoding that happens to all streaming videos.
Figure 1. Zebra stripes on my forehead tell me that lighting is optimal for my face.
Building Blocks of Good Exposure
Before getting to the camcorder, let’s discuss the non-camera related things that you need to have in place to achieve adequate exposure. First, you need lots of light. Anyone who’s ever been on stage or on a TV set knows how brightly the lights shine. That’s because even professional camcorders need lots of light to achieve good clarity. So, the first thing you should think about when shooting a presentation or webinar is to ensure adequate lighting. In most instances, you don’t need to go overboard; you just need to make sure that the faces are well-lit. Check out a quick lighting tutorial video I did that explains how to do this.
Be sure to use consistent lighting temperature between all of your light sources, which is a lot easier to do since incandescent bulbs largely went off the market. There’s a great tutorial on color temperature at go2sm.com/temp.
Next is choosing a good background and clothing for the subjects. This relates to the concept of “contrast ratio,” which is a device’s ability to discern detail in both the darkest and brightest objects in the frame. Your eyes have a contrast ratio of around 1000:1, meaning that you can see detail in dark objects and objects that are 1,000 times brighter.
However, a video camera has a contrast ratio of around 50:1, so it loses detail at the extremes of lightness and darkness. You see this in Figure 2 (below), where the same speaker perches in front of the same bookcase using (presumably) the same lighting and camera. On the left, the black shirt is a blob because the exposure properly prioritized the face. On the right, in muted browns and blues, the detail is preserved over the complete frame.
Figure 2. The excessive contrast ratio on the left turned the black shirt into a blob.
This is why you should always ask those who are about to appear on camera to avoid black and white clothing in favor of gray, blue, or brown. That way, you limit the contrast ratio in the frame and can capture good detail in both the lightest and darkest regions. Ditto for your background, which should contrast with your subject but not contain any regions that are either very bright or very dark.
Long story short, if you don’t have adequate light, your color temperatures don’t match, or you have extreme bright or dark regions in your frame, the exposure, color, and retained detail in your shot will be suboptimal. Because the video will be compressed, you should also avoid fine details in either clothing or background, no pinstripes or checks, but that’s a different issue.
A Word on White Balancing
White balancing is the process of telling the camera what is white. This is necessary because the color temperature of the lighting impacts the color of objects in the frame, which, like contrast ratio, is a problem exacerbated by the difference between what your eyes see and what the camera sees.
For example, imagine a whiteboard in a classroom. If it’s lit with fluorescent light, the board will have a slightly bluish tinge; if lit with incandescent light, it will appear slightly orange. Either way, your eyes see the whiteboard, your brain understands that it’s white, and tells your eyes that it is white. However, your camcorder doesn’t have the same knowledge, so you have to tell it the color temperature of the lighting.
With a professional camcorder, you do this by lighting the scene, pointing your camcorder towards a white object in the scene, zooming in so that the entire frame is white, and then pressing the white balance button. The Sony a6300 DSLR contains a number of presets, plus you can measure your color temperature with the camera and load that into a custom preset.
Just to close the loop, this white balance measurement is why it’s so crucial to use lighting with consistent color temperature. You see this in Figure 3 (below), where incandescent light with a color temperature of about 3000 Kelvin mixes with late afternoon daylight with a color temperature of 6000 Kelvin or higher. If you white balance for daylight, as on the left, the scene out the window looks normal but the subject’s white shirt looks slightly orange. White balance for incandescent light, and the shirt looks white but the background looks blue. If your white balance is this far off, you can’t fix this in a live shoot, or often even in post.
Figure 3. Mixing incandescent light in the studio with daylight from the window
Fortunately, most light bulbs and light kits now come with color temperature in the product specs if not listed on the bulbs themselves. This makes it easy to ensure that you don’t mix color temperatures. If you’re adding lights to existing lights in an office or meeting room, find out the color temperature of the existing lighting before purchasing or setting up the new lights.
Fundamentals of Exposure
Now that we’ve perfected the scene, let’s discuss our goal. Simply stated, the goal of setting exposure is to make sure that the most critical element of the frame is optimally lighted. In almost all instances, when shooting interviews, webinars, and other presentations, the critical element is the subject’s face. You adjust lighting using different controls on the camcorder and DSLR, but in both cases, you measure what’s adequate using the zebra stripes introduced earlier.
With the camcorder, the three controls are shutter speed, gain, and iris or aperture. Typically, you set your camcorder to shoot at 25 or 30 frames per second; shutter speed controls how long the shutter stays open when capturing each frame. The longer the shutter stays open, the more light enters the camcorder, which allows you to shoot in lower-light conditions. However, if there’s anything fast-moving in the frame, it might appear blurry.
According to the 180-degree shutter speed rule, you should set the shutter speed to twice the frame rate to mimic how humans experience motion in real life. So, if you’re shooting at 25p, the shutter speed should be 1/50th of a second; if you’re shooting 30p, set shutter speed to 1/60th.
I’m setting the shutter speed on my Panasonic camcorder in Figure 4 (below). One of the key features that sets professional camcorders apart from DLSRs are controls on the camera body. Having physical on-body controls as opposed to settings buried several screens deep in a menu simplifies accessing them during the shoot, particularly if you need to adjust them. You see the shutter speed buttons on the upper right; gain and iris are on the lower left, though hidden slightly by the LCD panel.
Figure 4. Setting the shutter speed on the Panasonic Camcorder.