BARRY BRAVERMAN /
10.01.2006
Originally featured on BroadcastEngineering.com
CAMERA CHARTS: Essential tools for broadcast shooters

An arcane camera reference chart, with its cryptic patterns and shapes interspersed with swatches of color, can be useful for some professional shooters. But for others, especially in the ENG realm, such an inscrutable tool is an alien concept that smacks of overkill.

Yet, for more and more shooters — particularly those toiling in the highly compromised realm of small-format HD — the all-to-often neglected reference chart is the key to establishing and maintaining consistent color, gamma and lens performance. For broadcast shooters, the simple camera chart has become a vital, indispensable tool that provides the foundation upon which we can apply every aspect of our craft.

Setting up shop

Proper camera setup has always been important in the broadcast industry. Years ago, I recall using a waveform and reference chart to verify the proper registration of my three-tube plumbicon Ikegami 79D. Decades later, the advent of 3-CCD cameras, with their multitude of presets and features, such as auto knee and news gamma, greatly simplified or even eliminated the imperative of a time-consuming and laborious setup.

However, substantial user input and tweaking is still required for creative and technical considerations, especially in the context of multicamera and dramatic high-end assignments. With respect to the considerable automation built into most modern cameras, there is only so much the engineers in Osaka, Seoul or Guangzhou can or should decide for us.

Proper camera setup using basic camera reference charts may be more critical than ever because the 1/3in 3-CCD HD cameras can often display less than impressive images, especially under low-light conditions. Macroblocking, accompanied by abundant noise apparent in all three color channels, is not uncommon.

These maladies are attributable in large part to the cameras' tiny 5mm imagers. Just as fine grain film increases resolution at the cost of low-light sensitivity, the miniscule pixels packed into small-format HD cameras significantly reduce low-light sensitivity.

Conversely, highlight latitude is also similarly constrained with decreased pixel size, which only underlies the most significant challenge facing HD shooters today: how to handle the performance compromises inherent to HD image acquisition in broadcast environments.

The peril of shooting HD is only exacerbated by HDV's extraordinarily high compression, which produces obvious hue shifts that can wreak havoc on flesh tones in the shadow areas. Add to that the Achilles Heel of modestly priced camcorders: their mediocre lenses. These lenses, interchangeable or not, produce abundant flare and chromatic aberration.

Now, professional shooters widely use HD, so they must commit more than ever to understanding the limitations of the format and the principal image acquisition tools, and then devise effective ways to address them. The proper use of camera reference charts can be key to establishing optimal aperture, focus and baseline.

Aperture

You don't need to 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. (See Figure 1.) 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 HD (or SD lenses used in HD applications) tend to fall short.

Backfocus

Accurate adjustment of backfocus is critical for HD shooters because the additional resolution offered by the larger raster demands precise, defined focus. Errors here become especially apparent to viewers with large-screen televisions and displays. Because of the high magnification, even the most unsophisticated viewer can easily discern focus, or lack thereof.

HD shooters must therefore remain vigilant for undesired softness. Many professional shooters' hard-won reputations have been sullied by a lens with an improperly set backfocus. (Note: The backfocus in cameras that feature a noninterchangeable lens is properly shaded at the factory to electronically maintain focus without breathing throughout the zoom range. This is a major advantage of the one-piece integrated lens camera design. A lens will perform better if its inherent limitations are mapped and compensated for as part of the inherent camera design.)

To set accurate backfocus and ensure sharpness throughout the zoom range, I typically place the camera 8ft to 10ft from the chart and set the lens in 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 filtration to achieve it. Viewfinder peaking should also be increased to about 80 percent to clearly see focus snap in and out.

In the past, I've used a simple star chart to perform this operation, and this pattern continues to serve me well. (See Figure 2.) The new FiddleHeads dual spiral design from DSC Labs represents a significant step forward. (See Figure 3 on page 90.) The patterns, when viewed in tandem, more clearly snap into focus. This attribute facilitates accurate assessment of any breathing apparent in the zoom lens.

Cameras 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 greatly facilitate the setting and evaluation of proper focus under a wide range of conditions.

Baseline

The ChromaDuMonde (CDM) chart can help the shooter establish a normal baseline for a particular camera and lens combination. (See Figure 4.) This baseline is akin to the look of a particular film emulsion type and can be modified or tweaked without limitation to accommodate the demands of a particular scene or scenes.

Camera manufacturers often deliver their cameras with default settings to suit what they perceive to be their primary user base. For example, some cameras ship with color matrixing and gamma parameters optimized for ENG applications. Shooters of other genres will likely find the images to be unusually brash and unforgiving until a proper baseline is established and new scene file created to reflect a more appropriate and pleasing look.

Using a vectorscope and evaluation grade monitor, the camera's normal color setup should be tweaked to place the CDM's targets in their respective boxes. (See Figure 5.) The camera gain may need to be raised to accomplish this to compensate for saturation discrepancies. (See Figure 6.) Of course, simply reproducing a full range of normal color may not ultimately be the look you're shooting for, but it's a valuable place to start. Skewing color one way or the other from normal to achieve creative goals will reduce the range of color actually recorded, so proper care must always be exercised during this camera chipping process.

Charting your own course

HD broadcast shooters, especially those working in small prosumer formats, must be cognizant of the limitations of their image acquisition tools. Notable defects appearing on screen, whether incurred due to high long-GOP compression, a mediocre performing lens or an anemic camera response in low light, can only be mitigated with the appropriate, optimal camera and lens setup.

Today, proper technique increasingly requires shooters to assert control over the extended post-camera workflow, to maintain their original look and vision. This includes precise color and density grading downstream. As professional shooters chart their destiny in this expanded workflow, one thing could not be in clearer focus: The proper use and understanding of basic camera references is critical to the exercise of our continued craft.


Barry Braverman is a veteran cinematographer with more than 20 years experience in feature films, documentaries and music videos. He is currently serving as a digital media expert and consultant to major studios. His latest book, “Video Shooter,” is available from CMP Books at www.cmpbooks.com.



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