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Shoot Expertise: Charting the Course

May 1, 2007 12:00 PM, By Barry Braverman

How camera reference charts can map out the world for the digital shooter.

There is probably little in our world less sexy than a camera reference chart. Its arcane layout of patterns and shapes interspersed with swatches of color can excite only the most techno-geek among us. Yet for digital shooters — especially those toiling away in the heavily compromised realm of small-format HD — the often-overlooked, often-misunderstood reference chart is the key to establishing and maintaining consistent color, gamma, and lens performance. Today, the deceptively simple utility that for so long wallowed in the province of socially challenged engineers has become a vital, indispensable tool in the modern shooter's toolbox. Indeed, it provides the foundation for applying the rudiments of your good craft.

Of course, proper camera setup has always been important. I can recall using a waveform and reference chart years ago to verify the proper registration of my three-tube plumbicon Ikegami HDK-79D. This was an essential procedure if acceptably sharp images were to be obtained. The advent of modern 3CCD cameras with automated presets greatly simplified — or even eliminated — the imperative of a laborious setup. However, substantial user input and tweaking is not only possible, but still highly advisable for the more savvy and accomplished among us — especially in the context of multi-camera and dramatic higher-end assignments. After all, there is only so much the engineers in Osaka, Seoul, or Guangzhou, China, can, or should, decide for us.

Today, proper camera setup using basic camera reference charts may be more critical than ever because the popular 1/3in., 3CCD HD cameras can often display less than impressive images — especially under low-light conditions. Macroblocking accompanied by abundant noise is not uncommon, a combination of maladies that can be attributed in large part to these cameras' tiny imagers. Just as fine-grain film increases resolution at the expense of low-light sensitivity, the small-format HD cameras with 1/3in. (actually 5mm) imagers are packed with ever-shrinking pixels that also greatly reduce low-light sensitivity.

Highlight latitude is also similarly constrained with decreased pixel size and increased sensor density, which only underlies the most significant problem facing HD shooters today: how to handle the performance compromises inherent to HD image acquisition. The peril of shooting HD is exacerbated by HDV's high compression, which may produce, among other artifacts, obvious hue shifts in the shadow areas that can wreak havoc on flesh tones. Add to that lower-end lenses, interchangeable or not, that produce abundant flare and chromatic aberration. With HD now a fait accompli in most of our lives, pro shooters must commit themselves to understand the limitations of the formats and their principal image acquisition tools, and then devise effective ways to address those limitations. Proper use of key camera reference charts can be the key to this effort.

The off-the-chart experience

One need not be the world's most ardent engineer to properly exploit the essential camera reference charts. The multiburst chart helps establish the optimum aperture setting for a lens by referencing differences in the upper and lower gratings in the chart grid. Altering the f/stop while adjusting the ambient light to maintain 100 IRE on the waveform will give you a good idea of lens performance at a given focal length, especially to the corners of the frame where mediocre lenses (or SD lenses used in HD applications) tend to fall short.

No turning back

Accurate adjustment of backfocus is especially critical for HD shooters because the additional resolution offered by the larger raster demands a more precise and clearly defined focus. This becomes especially apparent to viewers with the advent of large-screen TVs and projected displays because focus, or lack thereof, can be easily discerned by even the most unsophisticated viewers owing to the high magnification. HD shooters must, therefore, remain vigilant at all times for undesired softness. Many a craftsman's hard-won reputation has been sullied by a lens with an improperly set backfocus.

To set accurate backfocus and ensure sharpness throughout the zoom range, I typically place the camera approximately 8ft. to 10ft. from the chart and set the lens in the full-wide position. Setting the lens at maximum aperture is critical and may require adjusting the camera shutter or applying various levels of neutral density (ND) filtration. Viewfinder peaking should also be increased to about 80 percent in order to clearly see focus “snap” in and out.

In the past, I've used a simple star to perform this operation, and this pattern continues to serve me well. The new FiddleHeads dual spiral design from DSC Labs represents a significant step forward. When viewed in tandem, the patterns more clearly appear to snap into focus. This attribute facilitates accurate assessment of any breathing apparent in your zoom lens.

Camera models with an integrated lens system do not usually exhibit obvious breathing defects because the inherent soft spots in the lens are electronically mapped and corrected (i.e. shaded) at the factory. HD and HDV camcorder models with interchangeable lenses require scrupulous attention to backfocus, which should be checked daily during a production.

Look for a backfocus chart with a high dynamic range. The brilliant white and unusually dense black targets will facilitate the evaluation of proper focus under a wide range of conditions.

Going for a look

The ChromaDuMonde (CDM) chart can help the shooter establish a normal baseline for a camera-and-lens combination. This baseline, akin to the look of a particular film stock or emulsion, can then be modified or tweaked without limit to accommodate the particular demands of a scene.

Camera manufacturers often ship their cameras with default settings to suit what they perceive to be their primary user base. The Canon XL H1, for example, ships with color matrixing and gamma parameters optimized for ENG shooters. Shooters of other genres will often find such images brash and unforgiving until a new baseline is established with a more appropriate and pleasing look.

Using a vectorscope and an appropriate evaluation monitor, tweak the camera's color setup array in order to place the CDM's principal targets in their respective boxes. To compensate for saturation, you may have to raise the camera gain. Of course, simply reproducing a full range of color may not be the look you're going for, but it's certainly a nice place to start. Skewing color one way or the other from the normal will reduce the range of colors actually recorded, so you must always exercise proper care during the camera chipping process.

Charting your course

Digital shooters, especially those working in small-format HD, must be cognizant of the unique limitations of their tools. Between artifacts incurred with HDV's high compression and ample noise in the shadows due to poor low-light performance, the quality of our images simply cannot be ensured without a full understanding and proper setup of the camera.

Proper shooting technique increasingly requires us to assert control over the entire imaging workflow — which includes, among other things, precise color correction and compositing downstream — in order to maintain our creative look and vision. From a shooter's perspective, as we chart our futures in this industry, one thing could not be clearer: The proper use and understanding of basic camera references is critical to the exercise of our craft.

© 2008 Penton Media, Inc.