Add Depth to HD Shoots with Canon HD Lenses

What’s the lens got to do with it? In HD shooting, plenty. The lens is the arbiter between the live three-dimensional scene and the careful two-dimensional optical extraction from that scene. What the camera ultimately represents, digitally, is determined by the creative dynamic between the person controlling the lens (the DP) and the program’s director, lighting director, set designer, and of course, the talent. For drama work, a DP, working with the director and lighting director, can use a Canon HJ11ex4.7B lens (above) to capture a low-lit dramatic mood while defocusing background detail. On a shoot for a reality show, a Canon HJ22ex7.6B portable lens lets a DP follow an actor moving from extreme close-up to a distant point in the scene-across a thoroughfare, for example-while keeping everything else in the shot in sharp focus.

You can compensate for the loss of the third dimension, or depth, in a live scene by artfully exploiting depth of field (a strictly optical phenomenon) and perspective (the optical manipulation of foreground and background that is also a useful optical occurrence). The Canon HD cine lens HJ8x5.5 (above) has a maximum relative aperture of T-2.1. When used with a contemporary 24p digital HD camcorder (having a sensitivity specification of f-10 at 2000 Lux scene illumination) this can-under a scene illumination of a mere 50 Lux, and at a focal length of 20mm, with aperture set wide open-produce a depth of field of 24 inches. This helps direct your viewer’s attention to different actors in a verbal exchange when you pull focus between one actor and then the other. And when you’re shooting in digital, you can see how this looks in real time and make creative adjustments on the fly.

Some extreme wide-angle lenses let lens operators come close to emulating the extraordinarily wide field of view of the human eye. The zoom control (again a strictly optical tool) gives you real-time control over that field of view, and can be used to powerfully enhance the visual impact of a given scene. A wide-angle lens with a 4.7mm minimum focal length and an 11:1 zoom range can capture an incredible 90-degree horizontal angle of view-for example, a stadium 1,000 feet long from a distance of 500 feet. A long zoom portable HD lens, on the other hand, with a 40:1 focal range, can image a rare bird full screen from hundreds of feet away. Cinematographers, on the other hand, often like working with a tightly controlled limited range of focal lengths, and newer HD cine lenses offer zoom ranges tailored to such fine control. Canon’s new HJ8x5.5B KLL-SC, having an 8:1 zoom range combined with a very wide-angle 5.5mm, gives you an 82-degree horizontal field of view.

Because HD video is far richer in picture sharpness than the present SD NTSC television system, the added definition can add razor sharpness to a close-up shot. It can also sustain a very wide-angle shot that, by its very nature, is conveying to the camera a vastly greater amount of scene detail than the close-up shot. Film DPs understand that lens resolution is a complex science-it comes from years of trial and error on set. Real-time monitoring while shooting HD greatly empowers the DP’s control over lens-camera picture sharpness for different scene content.

How a lens maintains contrast is critical. A lens must never contaminate black reproduction-and high-performance lens designs go to enormous lengths to minimize such things as flare, veiling glare and reflections that can detract from a pure black reproduction. At the other extremity, where strong light sources in a scene and creative over-exposure, like sunlight through trees, might be important, the lens should minimize artifacts and unwanted reflections. You can only test the overall contrast performance of any given HD lens when it is attached to an HD camera. A test chart will quickly reveal the purity of the black reproduction and the accuracy of the grayscale reproduction over your nominal exposure range. Shooting into strong light sources, but moving the camera to position that source at the peripheries of the image, will show you how your lens is handling highlights and expose any optical anomalies.

The difference between an SDTV and an HDTV lens is huge. The HD lens needs to resolve 2.7 times more than the best SD lens-a significant extension in resolving power considering that both use the same small 2/3-inch image format. Over the past decade, astounding advances have been made that have led to this higher resolution, as well as the management of that resolution, from the center of the image to the corners, and the way it handles when a user controls the zoom, iris and focus.

One optical phenomenon common to all lenses-known as relative light distribution-occurs when the light transmitted through the lens falls off from the center out to the extremities of the image plane, impairing the contrast performance of the lens from its center to its corners. In turn, it adversely affects how sharp an image will appear across the screen. Canon took special steps, particularly in our FJs prime lens series (left), to achieve an especially even relative light distribution in its cine-style lenses.

Larry Thorpe National Marketing Executive Broadcast & Communications Division Canon U.S.A.

For more than 35 years Larry has been involved in video imaging. Fourteen of those years were spent in studio-camera development at RCA Broadcast and 20 years in HDTV market development at Sony Broadcast. Today Larry has moved out in front of the camera to market lenses for Canon. His fascination with video imaging, and HD imaging in particular, has resulted in many technical papers on the subject, published during the past several decades.

Never make the mistake of thinking that a lens is a mere accessory to the camera-especially in HD imaging. The HD lens has the primary role in shaping the image and giving it critical performance attributes that, in turn, will determine the ultimate digital performance of your camera.