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Case Studies
OPTICS AND ELECTRONICS: EVOLVING LENS TECHNOLOGY
By Gordon Tubbs, Assistant Director,
Broadcast and Communications Division at Canon U.S.A., Inc
Second in a series of three articles
In this article, we take a look at the progress in lens technology and how advancements enable greater productivity and ease of use for camera operators. It is important to understand that the lens has rapidly evolved in the past two decades. What began as a fundamental optical tool to create images for real-time scrutiny later became a primary tool for image capture. Along the way, the ingenuity of countless practitioners shaped this optical tool into a mechanism of creative intervention. Not only did the lens create the optical image for presentation but also it evolved as a powerful means of manipulating that image to augment the art and vigor of storytelling. In so doing, the lens became a powerful interpreter of the scene being imaged.
Since the lens is the first component to affect the video, the improvements we choose impacts everything else that happens to the image down the line. That’s why deciding what enhancements to make – and when – is a big responsibility. In most cases, features often start with the most common requests from end users. With that in mind, lens manufacturers look to make consistent progress on two fronts: the electronics that control the lens’ operation, and the optical properties of the glass and lens groups. First, let’s take a look at lens electronics since that’s where the most bold changes can take place due to the rapid advances in microprocessor capability that’s evident everywhere.
Lens’ Electronics: The move from Analog to Digital
The most dramatic area of improvement has been the transition from analog electronics to digital. This changeover began in the mid-90’s, and today covers all lenses made for HD- or SD-grade applications. The switch has not happened in pro video yet. In part due to the fact that this segment needs to be priced to sell to its market. Adding digital electronics would dramatically increase production costs and, in turn, price out the intended users.
In the latest-generation lenses, digital electronics incorporate microprocessors that are, for all intended purposes, miniature on-board computers that reside in the lens housing. These mini computers simplify the life of the camera operator and allow greater creativity. At Canon, for example, our Enhanced Digital Drive system provides a display on the lens that allows operators to visually access the lens’ memories and multiple features. This menu system can be viewed extremely easily and it is quite simple for operators to scroll through the visual display in order to enable and disable specific features.
For example, today’s lenses provide a memory function called Frame Preset that can memorize a frame at a specific focal length. With the push of a single button, operators can move the lens to a frame position and have the lens move at a memorized speed. In addition, the lens will be in focus when they reach that position.
This can now be done with two zoom and focus position memories, as opposed to the first generation of digital lenses which only had a single memory position for zoom and no memory position for focus. Such a feature has its advantages in studio productions such as daytime dramas, where the cameraperson may have to zoom in to the same position several times for multiple takes of a scene in order to achieve the same look again and again.
Another lens feature that today’s digital electronics make possible called Shuttle Shot is the ability to set a specific focal length on the lens in memory. Camera operators can simply hold down a single button and zoom to that position. When released the lens automatically returns to its original position. If the focal length happens to be a full telephoto position, camera operators can use the function to quickly check if they’re in focus and then go back to their original frame.
Other tantalizing possibilities with digital electronics that recently became a reality include the ability to limit the wide or telephoto focal length for certain applications – a handy function for operators who don’t want to go past the point where the f stop ramps, or go wider than a matte box would allow them to zoom. Going even deeper, camera operators now have the ability to actually control the reaction of the zoom by changing the zoom curve. With this feature, parameters of a zoom such as how the movement starts and speed of acceleration or deceleration, give it a specific look to the move or recorded image. In addition, the ability to have direct control or access to the lens via a PC is now available, which provides capabilities for advanced, on-the-spot troubleshooting.
It’s worth noting that while there used to be considerable differences between the digital controls available on ENG/EFP vs. box-style lenses, today both categories have the same high-performance capabilities. Whether you’re talking about portable or studio lenses one thing is for sure: lenses today can carry out functions that were not available – or even thought of – just five years ago.
Advancing Lens Optics: The Key to Image Quality
One of the interesting aspects of lens development is that research and development in optics operate on a different schedule than electronics. Change in electronics come to market quickly. Whereas affecting change in optical design is a very complicated science. That’s because there are many different types of glass and coatings interacting to produce imagery in the lens, adding to the complexity of designing optics.
Nothing affects image quality more than the optics. The precision and quality of the lens elements and coatings ultimately determine overall performance.
Now, let’s take a look at some of the advancements in the elements of the lens beginning with the type of glass used. The recent introduction of “Hi-UD” (High Index and Ultra Low Dispersion) glass makes it possible to decrease chromatic aberrations. Chromatic aberrations occur due to dispersion (the property that the refractive index of glass differs with wavelength). Hi-UD glass has a high refractive index and low dispersion rate thereby decreasing chromatic aberrations.
It is also important to understand the role of fluorite in dealing with chromatic aberrations. Researchers realized early on if they could manufacture artificial fluorite crystals and apply that to the lens manufacturing process they could decrease chromatic aberrations. Today, Fluorite is an essential part of producing high quality lenses; however, there are only a few companies in the world that produce it today. Optron, a Canon affiliate, is one of the industry’s leading producers.
Another key advancement in optics has been the increased quality of coatings to eliminate reflection. Coatings are thin transparent film on the lens surface that essentially uses interference to reduce reflection and increase transmittance. An example of a coating material would be magnesium fluoride. These coatings are very important for image quality due to the fact that anywhere between 4% and 10% of incidence light can reflect off all the elements of a lens. Lens manufactures, such as Canon, utilize multi-layer coatings that prevent reflection more effectively than a single layer.
The design of the lens is also critical. At Canon we utilize a design called the X-Element and the Power Optical System to achieve the highest possible specifications and decrease overall size and weight. In addition, Canon utilizes 3D CAD/CAM programs to speed up the design process and effectively deliver the best possible quality lenses.
One final note is that the integrity by which the lens is developed is as important as the advancements in technology and design. Canon consistently avoids using any materials or substances that could pollute the environment. The optical parts should feature lead free glass, designed to be completely non-polluting and the mechanical parts should be virtually free of all harmful products to the earth, such as cadmium, PBBS*, PBDPE* or mercury. *PBBS: Poly Bromo Bi Phenyls *PBPDPE: Poly Bromo Di Phenyl Ethers
Ultimately, lens development is all about reaching for higher overall image quality, while taking into consideration the overall production system and budgetary constraints. As an optical manufacturer, you never want to be stagnant – instead, you’ve got to always look ahead. Fortunately, when it comes to the development of both lens electronics and optics, there’s no end in sight.
Next month: How to make the most out of your lens: tips for studio and ENG/EFP setup and more.
Gordon Tubbs is Assistant Director, Broadcast and Communications Division at Canon U.S.A., Inc. He can be reached at gtubbs@cusa.canon.com
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