Image Stabilization

While increases in lens magnification has allowed directors to provide more compelling images to viewers, it has also made the job of a camera operator more difficult. In addition to focus needing to be perfect, lens movement and vibration can affect the image negatively.
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As television technology has grown ever more sophisticated in the last few years, so has professional lens technology. Camera operators have more control than ever over what they shoot—with manufacturers continuing to design lenses with increasing focal lengths, higher magnification and wider angles of view.

One area of lens technology that has seen the greatest development over the past few years is image stabilization. Lens development has become so refined that internal and standalone lens stabilization systems can now detect extremely subtle lens movements (such as those caused by a camera operator’s heartbeat) and correct them—reducing the chance of the operator recording shaky or blurry images.

How do these stabilization systems work? If you are a camera operator, it’s a question worth considering. After all, in order to take advantage of the increasing functionalities of broadcast lenses, it doesn’t hurt to know a bit about their technology. Today, there are two basic types of lens stabilization systems: electronic (sometimes referred to as digital) and optical. In electronic stabilization, compensation is applied to the image by a software algorithm after it has been digitized. While this approach may have economic benefits for the user, it has its limitations—one of which is that the subject must be well lighted in order for the software to determine its position.

Optical stabilization systems however, can work well under a variety of circumstances, so they are often a better choice. In this article, we will discuss how optical stabilization systems—particularly those developed by Fujinon—work.

Fujinon provides internal stabilization on a number of its lenses, including the XA76x9.3ESM HDTV and XA87x9.3ESM HDTV field lenses; XA87x13.5ESM and XA101x8.9ESM HDTV field super telephoto field lenses; and the HA42x9.7ERD HDTV and HA42x13.5ERD HDTV ENG/EFP stabilized telephoto ENG style lenses. For its other ENG-style and box-style lenses, it provides the TS-P28A and OS-TECH standalone optical stabilization systems, respectively.

Fujinon’s OS-TECH, TS-P28A, and internal stabilization systems all work in a similar manner. Essentially, they are feedback devices allowing for extremely sensitive motion detection within the lens system. In this way, they can eliminate the unwanted picture vibration caused by wind, support platform movements, or even the heartbeat of the camera operator. While the internal stabilization systems come built-in with the Fujinon lenses mentioned above, the OS-TECH and TS-P28A can be attached, “sandwich-style,” between the camera and various lenses. An internal version of the OS-TECH system is also an available option on Fujinon’s XA76X, XA87X and XA101X series field lenses.

In order to understand how Fujinon’s optical image stabilization works, it’s useful to imagine the mechanics of the lens in an ideal situation, capturing an image with no movement—not even the slightest vibration—whatsoever. In this situation, the lens would be perfectly perpendicular to the ground. The light from the center of its subject (i.e., the optical axis) would line up with the physical axis of the camera perfectly. The result of this is that the center of the subject is projected onto the exact center of the lens’s CCD. This is the ideal—what the inside of the lens would look like with no vibration whatsoever.

Now let’s tackle the reality: There is always going to be some vibration of the lens, no matter what. It’s inevitable. When a vibration occurs, the lens will shift slightly. For our purposes, think of it as shifting up or down slightly. When that happens, the optical axis no longer lines up with the physical axis perfectly. The center of the subject is no longer projected onto the exact center of the CCD. Rather, it is projected somewhere above or below the center of the CCD, a situation that can lead to a blurry or shaky picture.

When this situation occurs (and it occurs constantly), Fujinon optical stabilization technology compensates for it by making the image appear as though it is being projected onto the center of the CCD—perfectly lined up with the physical axis of the lens. Here’s how the system works: Both the OS-TECH and the TS-P28A have built-in vibration detectors (accelerometers)—one for horizontal vibrations and one for vertical vibrations (the internal optical stabilization systems have similar mechanisms)—they also have a moveable compensation lens, whose purpose is to adjust the position of the image on the CCD. When a horizontal vibration is detected, that movement is filtered, amplified, converted from its natural analog state to a digital signal and output to the lens’s central processing unit (CPU). The same thing happens when a vertical vibration is detected (vertical and horizontal vibrations can be detected and compensated for at the same time).

At the same time the vertical and horizontal vibration data is being fed into the CPU, information about the focal length and type of lens is also being fed into it. The CPU uses this information to make a calculation of how much compensation is needed. This output is fed into the D/A converter, which converts the signal back to analog. The now analog signal is fed to the drive circuit, which controls the vertical and horizontal motors that move the compensation lens. The entire effect is to make the image on the CCD appear not to have moved. Keep in mind that this stabilization system is not static. It is working continuously with the lens, over and over again.

Fujinon optical stabilization systems can compensate within a range of 1-10Hz and 30% of the image height. As long as you keep within this range and image height, the image projected on the CCD will appear not to have vibrated at all. Another feature of the systems is a proprietary algorithm that eliminates “after shaking,” a result of the stabilizer continuing to operate after the operator has stopped all pan/tilt motion.

For more information on Fujinon’s optical stabilization systems, go to www.fujinonbroadcast.com.

David Waddell is the marketing manager of Fujinon’s Broadcast and Communications Division.