SVG Tech Insight: Operational Innovations in 4K UHD Broadcast Television
This fall SVG will be presenting a series of White Papers covering the latest advancements and trends in sports-production technology. The full series of SVG’s Tech Insight White Papers can be found in the SVG Fall SportsTech Journal HERE.
Challenge of Focus Control for Live Sports Coverage
Especially on live broadcasts of major events where production directors choreograph dozens of camera feeds, the operational pressures can be considerable. The individual camera operator can, at any moment, be simultaneously actuating one or all of the four primary lens-camera operations of image framing (zoom demand), focus on chosen subject (focus demand), operational panning and tilting, and focus tracking on moving subjects.
Second-generation 4K UHD long zoom telephoto lenses have introduced significant advances on the both operational side and on the performance specifications. Focal ranges were extended, 4K image sharpness improved across the image plane, HDR/WCG functionality added, and improvements in built-in image stabilization systems [1].
4K UHD poses severe challenges to achieving razor sharp focus in a small image format like 2/3-inch. The sensitivity of the focus control increases as the resolution of the television system increases — in terms of a rapid drop in sharpness with only a small movement of the focus control knob. The challenge is exacerbated in that 4K UHD broadcast cameras still utilize HD viewfinders — and these are very limited in size, whereas the final 4K image will be typically viewed on large 4K displays that clearly expose even the smallest shortfall in focus precision.
The small 2/3-inch image format is often linked to deep depth of fields, and hence some degree of latitude in controlling the lens focus. However, this can be extremely variable depending upon the actual shooting environment and associated lens settings. Daytime or nighttime scene illumination and lens aperture setting, subject distance from the lens, focal length setting — all collectively contribute to very wide ranges of depth of field, especially in sports coverage, as typified in Table 1.
Table 1: Three long lens shooting situations that show the variability of depth of field.
For a 4K UHD lens-camera system based on the small 2/3-inch image format size, the depth of field restrictions become more severe and the challenge to achieving sharp focus escalates.
Given the special operational demands of 4K UHD 2/3-inch cameras — and with 8K UHD cameras already looming — it was believed that another level of both Zoom Demand and Focus Demand controllers would be an important addition to the existing family of broadcast controllers. These would offer heightened degrees of operational control over both zooming and focusing operations. In particular, given the growing addition of large format lens-camera systems within the sporting world, they would bring to the small 2/3-inch image format broadcast lens operational capabilities that emulate long-established capabilities in the precision focusing operation of those larger format cinema lenses.
New Focus Demand – Resolving the Challenge of Focus Accuracy
A new focus demand having a built-in electronic display supports the presetting of a range of operational modes relating to lens focusing. The display portrays the optical focus range and, below this, it displays the physical control range — two key programmable parameters that determine the chosen mode of operation. It takes 2.5 turns of the Focus control knob to manually cover the total focus range. This, in itself, does apply a degree of Vernier control of focus, which works well when the lens settings favor a reasonably deep depth of field. But, now this can be considerably augmented.
Television outside broadcasts entail a wide range of shooting environments that place quite different operational requirements on the camera operator. The ability to separately preset the optical focus range and the control knob range is a significant new innovation that offers new imaging flexibilities. In the context of sports coverage — one extreme might be the need for the lens-camera system to be moved rapidly between two individuals separated by a considerable distance — requiring a significant degree of optical re-focusing to be rapidly implemented. Here, the large change in optical focus would best be achieved with a small turn of the focus control knob, which is not possible with standard controllers. An alternate situation might entail a precision facial close-up of an athlete who is a great distance from the lens. In that telephoto setting, the ability to implement a minor optical focus adjustment with a wide (or multiple) rotation of the control knob facilitates a precision vernier adjustment that helps ensure a perfect capture of tension or emotion on that face. Two specific pre-settable focus modes (others are also available) are now described to illustrate the flexibilities offered by the new Focus Demand.
Scenario One: Fine Focus Mode
The value of this mode is best illustrated by consideration of a 4K field lens-camera system located within a stadium and imaging a player or athlete a considerable distance away on the field. The director is interested in capturing a moment of concentration or emotion in a facial close-up. The lens is zoomed to achieve the desired framing of the chosen subject and the focus control is rotated to anchor the chosen subject distance. With the aid of the built-in display and the control buttons integral to the new Focus Demand, simple adjustments are now made to preset two limits around that central focusing setting — producing the desired small focus operational range. Now, range of motion of the control knob is expanded — the 2.5 turns that previously covered the entirety of the focus range of the lens is instead dedicated to that programmed restricted range of optical focus. This allows a beautifully smooth and slow zeroing in on razor-sharp focus of the chosen subject, as illustrated in capturing the concentration of an athlete awaiting the firing of the starting gun in Figure 1.
Figure 1: Principle behind the setting of Fine Focus Mode 1 to empower razor sharp focus on a facial close-up.
By choosing the degree of the restricted range, the Focus Demand can achieve a highly precise 4K image sharpness, which is especially valuable on facial close-ups. A variation on this scenario might allow the camera operator to implement precision rack focus between various athletes, adding a degree of creativity to the live production.
Scenario Two: Control Range Limit
In a sense, the Control Range Limit mode is the opposite of the Fine Focus Mode. This sets dead zones in the demand movement range and enables greater optical focus range with smaller rotation angle with the focus adjustment range kept as-is. This is ideal for alternating focusing, such as at a tennis rally, where the active focus range has been preset to allow rapid refocusing on each player with a minimum rotation of the focus knob, as illustrated in Figure 2.
Figure 2: Curtailment of the active Focus range that accommodates easy focus change between both players.
Focus Curves
The Focus Curve selector switch on the Focus Demand lets operators switch the focus position in relation to the focus knob position, between one straight line and two basic curve modes, known as the Far Mode and the Near Mode. The Far Mode — associated with Infinity — is the curve in which the focus position changes very slowly the more the knob is turned toward the infinity side. This makes fine focus adjustments easy on the infinity extremity of focus. The Near Mode is the opposite of Far Mode, in which focus position changes very slowly the more the focus knob is turned toward the close side. This makes fine adjustments easy on the MOD extremity of focus.
New Zoom Demand
This new Zoom Demand controller has all of the operational functions of the standard Zoom Demand including Frame Preset/Shuttle Shot/Speed Preset. However, the new Zoom demand has additional important features: user settings can be registered and operational functions can be assigned to switches from the display screen. Preset speeds can also be set, and zoom control curves can be selected. Users can also check connection status and see whether various functions are on or off.
Zoom Control Curves
With Zoom Demand, the zoom speed control can be programmed to have different characteristics in relation to the control thumb ring rotation angle. There are preprogrammed control patterns within the controller that are termed the Zoom Curves. One Curve offers a faster zoom speed with smaller thumb ring rotation angle, making it ideal for high-speed zoom operation. A second Curve is the opposite — making it useful for operation at lower zoom speeds. A third Curve is midway between the former two.
Summary
As discussed in a previous white paper [1] significant steps forward were made simultaneously on the operational specifications and on the optical performance specifications of second-generation long-zoom 4K UHD field lenses. Equally remarkable is the parallel development that was also ongoing in addressing those identified challenges in 4K UHD imaging; namely, the operational impediments to ensuring sharp focus in shooting environments that can be particularly difficult. The development of the new Focus Demand and Zoom Demand controllers are innovative flanking accessories that further empower camera operators in live sports coverage.