Chapter 4 n Choosing a Camera |
81 |
Image Stabilization
Because it’s difficult to hold a oneor two-pound camcorder steady, most cameras now provide some sort of image stabilization feature to smooth out bumpy, jittery camera movement. Image stabilization technology—though no substitute for a tripod—is very effective and (usually) has no ill side effects.
There are two kinds of image stabilization: electronic and optical. Digital image stabilization (DIS, sometimes called electronic image stabilization) requires an image sensor with a larger imaging size than the actual image size that is displayed. DIS works by detecting camera motion, analyzing it to see if it’s intentional or not, and then digitally moving the image to compensate for unwanted motion. Because the camera is overscanning the actual field of view, there are enough extra pixels around the edges to allow for this kind of movement (see Figure 4.19).
Figure 4.19
In digital image stabilization, the camera scans an area that is slightly larger than the recording video and then adjusts the frame to compensate for shake.
Since the camera is constantly moving the image about the screen to compensate for shake, electronic stabilization can often result in softer, slightly blurred images. We’ve also seen some cameras show a slight color shift when using DIS. However, most DIS functions in use today do an excellent job of stabilizing the image without noticeably degrading the quality.
Optical image stabilization (OIS) doesn’t alter your image, but instead changes the internal optics of the camera to compensate for motion. In an OIS system, the lens can reshape some of its optical elements to redirected light onto the correct part of the image sensor(s) to compensate for camera shake (see Figure 4.20).
Since OIS doesn’t ever touch your image data, there’s no chance that it will corrupt your image. On the downside, because it’s more complicated, optical stabilization costs more than electronic stabilizing. Also, because the stabilization is tailored to a particular lens, if you add wide angle or other attachments that change the focal length of your lens, OIS will stop working.
When evaluating a camera, try some motion tests—both slow and smooth, and fast and jittery— to see how each camera’s stabilization feature affects overall image quality.
82 The Digital Filmmaking Handbook, 4E
Figure 4.20
Optical image stabilization works by reshaping one of the lens elements on the fly to correct for camera movement.
Image Stabilizing in Post
Thanks to the high-resolution of HD video, stabilizing shaky footage in postproduction is a viable option. Check out Chapter 17, “Titles and Effects,” for more on this subject.
Viewfinder
Most video cameras have two viewfinders: an eyepiece viewfinder and a flip-out LCD viewfinder. Because you can tilt an LCD into different viewing angles, flip-out LCDs afford you a wider range of shooting options. However, because an LCD drains your battery quickly and can be difficult to see in bright light, you might not be able to use it all the time. Yes, you want a high-quality LCD, but don’t let LCD quality weigh too heavily when choosing a camera.
Some higher-end cameras include a feature called zebra stripes that displays diagonal black- and-white lines in areas of your image that are overexposed. These lines are not recorded to tape; they only appear in the viewfinder. If you’re manually setting your shutter and iris, zebra stripes are a must-have for situations when you don’t have an external monitor to look at (see Figure 4.21). Top-of-the-line cameras let you set the brightness level at which the zebra stripes appear. This is useful if you are trying to shoot with a low-contrast ratio, as is sometimes recommended for video-to-film transfers.
Many professional shoulder-mount video cameras and digital cinema cameras do not have LCD displays, but in some cases, there are special separate LCD viewfinders that can be added onto the camera. Often, a field monitor is used to see what the camera is shooting on a larger display. If you are shooting HD, this field monitor needs to be HD as well, or else you won’t really be seeing the image that is actually being recorded. To send true HD video out to a field monitor, you’ll need a camera that has an HDMI or HD-SDI cable output.
Chapter 4 n Choosing a Camera |
83 |
Figure 4. 21
The diagonal lines in this viewfinder are the “zebra stripes” that indicate overexposure.
Interface
All cameras today are small computers, and even consumer cameras have complicated menus and settings. At the lowest end, you’ll find the menus written in plain English; at the highend, unless you’re an experienced camera operator, you’ll need the manual to make sense of the menu items.
Typically, the menu interface offers control over the following:
nFormatting media.
nSetting date and time. This is important if you are using time of day to synchronize multiple cameras together.
nVideo recording format. Most cameras offer a selection of image sizes and frame rates.
nWhite balance and color presets.
nAbility to turn off automated features, such as auto focus, auto iris, and so on.
nPreview and playback features.
nIn-camera special effects.
In addition to the menu options, most video cameras offer status displays in the viewfinder or on the LCD screen. A good camera warns you when your battery is running low or when you are running out of space to record media. Some cameras are definitely better at this than others.
Avoid In-Camera Special Effects
Most video cameras, especially lower-cost cameras, include a number of special effects ranging from sepia tinting to “arty” posterizing looks. We don’t recommend using any of these features. It’s better to shoot unprocessed video so as to have the greatest flexibility during postproduction.
84 The Digital Filmmaking Handbook, 4E
Audio
It’s pretty safe to say that the microphones included on almost all camcorders are lousy. Lowquality to begin with, their usefulness is further degraded by the fact that they often pick up camera motor noise, as well as the sound of your hands on the camera itself. Consequently, an external microphone jack and a headphone jack are essential for quality audio recording. In addition to replacing the lousy onboard mic on your camera, an external mic jack lets you mix audio from a number of mics and feed the results into your camera. We’ll discuss audio hardware more in Chapter 8.
Ideally, you want a camera that has XLR mic connectors that can be switched between mic and line-level inputs. Many lower-end cameras offer a small TRS mic jack instead of XLR, which is okay if it suits the type of mic you plan to use. Make sure the connectors are positioned so that mic cables and connectors won’t get in the way of moving the camera and shooting (see Figure 4.22).
Figure 4.22
This JVC GY-HM100 is an entry-level professional camcorder that provides excellent audio controls.
A headphone jack is a must-have to ensure that you’re actually recording audio. (You’ll be surprised at how easy it is to forget to turn on a microphone.)
Manual audio gain controls let you adjust, or attenuate, the audio signal coming into the camera, making it easy to boost quiet voices, or lower the level on a roaring car engine. At the lower end, very few cameras have audio meters and manual adjustments although some can display level meters on the LCD screen. This isn’t a deal breaker, but they’re nice to have if you can get them.
Many cameras have an auto gain control or auto limiter, which will automatically try to limit loud noises. Unfortunately, like many automatic features, since you have no control of an auto gain feature, you can’t always be sure that it’s not limiting your sound more than you’d like or perhaps worse, boosting the audio unnecessarily. Again, these features aren’t deal breakers, but if your camera is outfitted with such a limiter, you’ll need to experiment with it to learn how sensitive it is. Ideally, your camera will allow you to disable this feature if you want.