A video reference design: the Canon XH-A1 camcorder
Since we have examined the video capabilities of still cameras, let’s also look at an actual, dedicated video camera to see what professional videographers are used to and might reasonably expect.
The $3999 Canon XH-A1 uses three 1/3” CCD sensors, each with a native resolution of 1440x1080 (about 1.56 megapixels). The sensor’s output can interpolate to full HD resolution of 1920x1080. It can record in either SD or HD resolutions, and SD can be switched between 4:3 and widescreen 16:9 proportions. It has a built-in 20x zoom lens with a 35mm equivalent focal length range of 33-650mm at 16:9, or 40-796mm at 4:3. The lens has a widest aperture that varies from f/1.6 to f/3.5 over the focal range. It takes 72mm external filters, and includes built-in 1:6 and 1:32 ND filters.
The XH-A1 has the classic “lunchbox” design that is popular among ENG-style cameras: boxy body, large lens dominating the front, swing-out LCD display on the left, tape bay and grip on the right, tote-handle at the top supporting a hotshoe, electronic viewfinder at the back, and built-in stereo mike (that nobody uses) at the front. To the right of the built-in mike and the lens, are two essentials that were an external option on the earlier GL series: a mounting bracket for an external mike (which is why nobody uses the built-in), and an XLR input adapter for two external mikes.
|External XLR microphone inputs
||The zoom, focus and iris rings on the 20:1 zoom lens
The camera records up to 1 hour of DV or HDV video data to a mini-DV tape, which goes into a tape bay on the right side of the camera. Controls for the tape (Play, Pause, Stop, Rewind, Fast Forward, etc.) are in the tote handle at the top. Video and control data can also be streamed through the FireWire port to an external hard disk or computer. The camera can also take still pictures (up to 1920x1080 or about 2 megapixels) which are recorded on an SD or SDHC flash card and can be downloaded via a USB2 port to a computer.
Ergonomically, the camera is held freehand by the right hand cupping the side of the body under a grip strap. The right thumb toggles a Record Start/Stop button. The right index and middle fingers operate a Zoom In/Out switch. All of these frequently-used controls fall naturally under the hand. The left hand operates control rings (for zoom, focus and iris) on the lens, audio level dials, exposure controls, and miscellaneous other controls scattered about the top and left sides of the camera.
|The zoom switch
||The exposure mode dial
Composing shots is critical to good video, and visual feedback is essential. This can be done either through a swing-out 2.8” LCD display panel on the left side, or the electronic viewfinder (EVF) at the back of the handle. The LCD panel tilts and swivels so that it is visible from many points of view – high shots and low shots are doable as well as the usual head-on shots. The LCD panel can even be swiveled to face forward so subjects can monitor themselves (if not too far away) – the image can be flipped and mirrored so that it looks right to them. The EVF also tilts up and down, to adjust for the best eye angle when, say, the camera is mounted on a tripod or shoulder brace. Note that the EVF consumes less power than the LCD panel, so is a better choice for extended operation, and it is also more viewable in bright outdoor lighting.
Sometimes the small LCD display panel may be inadequate (consider that studio situation where the subjects want to watch themselves but the LCD might be too small and far away). The camera has an A/V output port so that the audio and video can be played on an external large-screen monitor as they are recorded. (This can also be used to hook up a small but remote LCD monitor when, say, the camera is mounted at the end of a long boom, or on a Steadicam rig.)
Focus, of course, is as important in video as in still photography. The camera provides multiple options for focusing. Focus can be set to either Manual or Autofocus. In Manual mode, one turns a focus ring on the lens. (This ring can even be operated while in Autofocus mode, to make a temporary manual override.) A popular style of manual focus is to prefocus with the zoom racked all the way in, then zoom back out to recompose for shooting. The camera also provides two display modes to assist manual focus. Peaking emphasizes the subject’s edges (outlines), and a 2x magnifier can also be turned on. Autofocus mode tells the camera to focus on the subject in the center of the screen. A “Quick Autofocus” mode (that works better in low light than normal autofocus) can be used to quickly find focus, even in manual focus mode. The camera can also be told to remember a particular focus setting, and return to it (at a controlled speed) at the push of a button.
Since zooming is very visible during video, how it is done matters. The user has several choices for zoom control on the camera, ranging from freestyle to very precise and controlled. The zoom ring on the lens can be turned directly. Or the zoom switch near the side grip can be pressed. The zoom speed can be set to any of 16 constant speeds in response to this switch. Or the zoom switch can be configured as a variable-speed control, so that the speed varies depending upon how far the switch is pressed. For those occasions when the camera is being used for low-angle shots, there are zoom buttons mounted on the top of the tote handle (since the side grip is less accessible then). There is provision to memorize a particular zoom setting and return to it at the push of a button. Zooming can also be directed via the wireless remote supplied with the camera, or an external controller plugged into the LANC remote-control port. (These are useful for “balcony shots” or when the camera is mounted on a boom for aerial perspective shots.)
Good audio, too, is critical to good video, a fact often overlooked. This is why the built-in microphone is so seldom used – it picks up too much internal operating and handling noise from the camera, and cannot always be placed optimally to pick up the subject. The camera’s external microphone inputs allow outside mikes (either mounted on the camera or placed remotely) to be used. These can be positioned as close to the subject as necessary, and can have the pickup pattern (omnidirectional, cardioid, or supercardioid AKA “shotgun”) that’s best for the situation. A wireless lavalier mike can be clipped directly to the subject and the receiver mounted on the camera’s hotshoe, a popular solution for weddings and interviews, for example. Besides audio inputs, the camera has a headphone output jack, so the audio can be monitored for quality as it’s recorded. Some of the troublesome audio artifacts one might want to watch for are hiss (at low audio levels), clipping (at high audio levels), wind noise, sibilance, background noise (jackhammers, airplanes, automobiles, appliances, cellphone chatterers, etc.) – knowing you have a problem, you can either correct it on the spot or do a quick retake. To help monitor audio level, the camera can display it in simulated “VU” meters on the display or EVF, and individual volume controls for each channel allow the recorded level to be corrected.
Sometimes the audio is so critical that even external audio inputs are inadequate. For a music video, for example, one might want to record more than two channels of audio (miking each instrument separately), and mix them down later. The audio can be recorded with external equipment, and aligned with the video in postproduction (editing). While doable, this is a pain unless some sort of synchronization signal is provided. “Clapper boards” at the start of each scene can provide such a signal (the sharp audio peak from the clapper). The XH-A1’s big sister, the XH-G1, can also embed a continuous reference signal (SMPTE timecodes) in the recording, which can then be aligned with similar timecodes in the audio recording when they are combined in editing.
For quick and dirty work, the camera can also be set to control the audio levels automatically.
A wide range of exposure modes are selectable via a large dial on the left side of the camera:
· Easy Recording – the camera makes all the decisions. There is no manual control whatsoever.
· A (Auto) – like Easy Recording but with the option for manual overrides.
· Tv (Shutter Priority) – Manual setting of the shutter speed (from 1/3 to 1/15000 sec), with aperture selected automatically. This mode is best for shooting fast action. It can also be used to reduce flicker when shooting under certain kinds of lighting (fluorescent, mercury vapor, etc.) by setting the shutter speed to 1/100 or below.
· Av (Aperture Priority) – Manual setting of the aperture (from f/1.6 to f/9.5) with automatic selection of the shutter speed. This mode provides the most control over depth of field.
· M (Manual) – allows complete freedom to set all exposure controls as you wish, even to technically “wrong” values. Offers the most creative flexibility.
· Spotlight – a convenience mode that automatically controls the exposure for situations in which the subject is centrally lit, such as by a candle or stage spotlight.
· Night – another convenience mode, providing automatic control optimized for subjects in dim light.
The aperture itself is set by rotating the iris ring on the lens. The shutter speed is set by a dial on the left side of the camera. An exposure lock can be used to freeze the exposure, and exposure can also be compensated up to 2 stops over or under, in the A, Av or Tv modes. The camera also has a “Clear Scan” mode for recording computer or TV monitors without the black banding artifacts that often occur on these.
White balance can be set to outdoor (sunlight, 5600K) or indoor (tungsten, 3200K) standard presets, or to an arbitrary color temperature (2800-12000K), or to either of two custom WB presets.
The camera can record in a variety of frame rates, to accommodate production for various media. At 24fps, a choice of methods is provided to align the filmlike 24fps rate with the 60i rate used for television display.
· The “60i” mode (60 fields per second interlaced) matches the timing of standard-definition television.
· The “30F” mode records video in “30p”, or 30fps noninterlaced (AKA “progressive” scan). When displayed on a 60i monitor, each frame will be output twice to simulate the two fields of an interlaced display.
· The “24F” mode records at 24fps progressive scan. When output to a 60i monitor, timing is adjusted by the “2:3 pulldown” method, where the first frame is output twice, and the next frame is output three times, per cycle. This mode gives the closest approximation to a 24fps “film” look.
· The “24F 2:3” mode actually records a 60i signal downconverted from 24p by the 2:3 pulldown method described above.
· The “24F 2:3:3:2” mode alternates the pulldown between 2:3 and 3:2, otherwise it is like the “24F 2:3” mode.
This is not a review, just a summary of the basic specs and capabilities of this camera. It is meant to give an idea of what professionals expect from a video camera, to put the new “video-enabled” DSLR offerings into context.
Summary of key specifications and features:
· Three 1/3” CCD sensors
· 1440x1080 pixels native resolution (circa 2 megapixels)
· Supports HD video resolutions up to 1920x1080
· Supports both 4:3 and widescreen 16:9 image proportions
· DV or HDV video format recorded mini-DV tape
· Can record to external hard drive via FireWire interface
· Records audio from built-in stereo microphone or external XLR jacks
· Outputs video to A/V or HDMI connectors for realtime display
· Interfaces to computer through USB 2.0 port or FireWire interface
· Supports ISO 100-6400 at all resolutions, and 50-25600 at reduced resolutions
· Has a hotshoe for external flash
· Has both an electronic viewfinder, and a 2.8” swing-out LCD screen
· Supports Easy, Auto, Shutter priority, Aperture priority, Manual, Spot, and Night (low-light) exposure modes during video
· Supports Sunlight, Tungsten, Arbitrary Kelvin, and two Custom white balance settings
· Supports 60i (interlaced) as well as 30F and 24F noninterlaced framerates
· Supports a variety of “pulldown modes” for scanrate conversion
· MSRP (suggested retail price) is US $3999.00
· Excellent ergonomics for video shooting
· Excellent external audio connectivity
· Versatile control options for focus and zoom
· Flexible options for manual vs. automatic exposure control
· Wide range of video scan rates supported
· CCD sensors are immune from rolling-shutter artifacts
· Three sensors provide low noise and good light sensitivity
· Non-interchangeable lens
· Sensors are smaller than those on DSLRs, so potential depth-of-field is not as shallow
· Built-in mike picks up operating and handling noises