How Canon breaks new ground in 4K broadcast lenses

A range of Canon pro video lenses sit against a black and red background.
2018 marks Canon's 60th year of manufacturing broadcast lenses. Ever since the 1958 launch of the innovative IF-I 60-400mm f/4 lens, Canon has continued to listen to broadcasters and cinematographers to develop lenses based on industry trends and needs.

Building on its heritage in innovative lens design, Canon has bolstered its professional 4K broadcast lens range with the launch of three new lenses: two broadcast field zoom lenses in 4K Premium optical quality, the UHD DIGISUPER 122 and the UHD DIGISUPER 111, and a portable zoom lens in the high-end UHDxs series, the CJ25ex7.6B.

The UHD DIGISUPER 122 and UHD DIGISUPER 111 have exceptional optical performance, exceeding 4K expectations with broad-ranging focal lengths, high zoom ratios and class-leading operability. Achieving descriptive power and outstanding colour reproduction from the wide end to the telephoto end, these lenses allow realistic and high-resolution shooting – ideal for outdoor sports broadcasting, as well as indoor events, such as concerts.

Canon’s flagship field zoom broadcast lens, the UHD DIGISUPER 122, can deliver the world’s widest angle and world’s longest focal length – 8.2mm at the wide end and 1,000mm at the telephoto end – as well as the world’s highest zoom ratio of 122x. Meanwhile the UHD DIGISUPER 111, with a 111x zoom ratio and a focal length range of 8.3mm to 925mm, aims to become a golden standard among broadcast productions where high zoom ratio is required.

A visitor tries out the latest Canon broadcast lens release on its stand at IBC 2018.
Canon’s flagship field zoom broadcast lens, the UHD DIGISUPER 122, can deliver the world’s widest angle and the world’s longest focal length – 8.2mm at the wide end and 1,000mm at the telephoto end – as well as the world’s highest zoom ratio of 122x.

With optimal lens placement, precision and design, these lenses deliver performance beyond 4K, delivering high-resolution and high-contrast video capture from the centre to the edges of the screen. The broadcast lenses are also the first to utilise Canon’s proprietary Air Sphere Coating (ASC), which reduces flaring and ghosting – ideal for shooting in HDR and Wide Color Gamut (WCG) – making high-tonality visual expression a reality.

The CJ25ex7.6B

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Adding to Canon’s UHDxs series of portable zoom lenses for 4K broadcast cameras with 2/3-inch sensors, the CJ25ex7.6B features fluorite and Ultra-low Dispersion (UD) glass, and a proprietary optical design focused on the optimal placement of elements. This reduces chromatic aberration from the centre to the edge of the image, across the entire zoom range. This CJ25ex7.6B offers a 25x zoom ratio, covering a focal length range from 7.6mm at the wide end to 190mm at the telephoto end, to support a broad range of shooting scenarios.

The portable zoom lens also delivers high resolving power and high contrast to facilitate high-resolution video capture, while the lens coating technology and design prevents reflections within the lens barrel, reducing ghosting and flaring. This maximises the superlative colour reproduction, which is ideal for HDR and WCG video shooting. Alongside its considerable 4K optical performance, the CJ25ex7.6B offers a compact and lightweight body design that weighs approximately 1.99kg and measures 169.6mm (width) x 114.1mm (height) x 223.3mm (length). It is highly manoeuvrable and ideal for a wide range of indoor and outdoor shooting scenarios, including sporting events and news reportage.

The broadcast lens area at the International Broadcasting Convention 2018.
The broadcast lens area at the International Broadcasting Convention 2018 in Amsterdam, the Netherlands, where industry professionals convened to test and try the latest Canon releases.

A history of innovation

Research and development is central to Canon's ambition to improve the experience of filmmakers and photographers. While cameras are key, it's the lenses that complete the system and help directors and cinematographers to bring their visions to life. Talking to the market to find out what products and features people want is key – the first step in creating a market-leading product.

It is demonstrated with Canon's Electronic News Gathering (ENG) lenses. In the last few years there has been a shift in the industry, with large-format Super 35mm sensor cameras being used not just for cinema but also in the TV broadcast arena. This led to a desire for a Super 35mm lens that could cope with both working methods – fully manual for cinema, or with a drive unit to suit TV production. The CN7x17 KAS S was one such lens and received acclaim from both audiences. In communicating with the market, Canon discovered that among people working in wildlife, sport and documentary fields, there was also an appetite for an ultra-telephoto lens.

In initial conversations it was found that operators were using lenses such as the HJ40x14B IASD-V with a lens mount adapter to achieve the extended focal length they required. Additionally, producers were using the CN-E30-300mm T2.95-3.7 L S lens but required longer focal lengths, ideally of 1,000mm. In addition to this focal length requirement, it was found that users wanted a lens that was lightweight, offered 4K optical performance, and around the same size and weight as the CN-E30-300mm T2.95-3.7 L S.

During the course of Canon's interviews, one customer took out the CN-E30-300mm and asked, 'Can you make an ultra-telephoto lens that is this size and weight?' This gave the development team a clear brief in terms of compactness and lightness.

Meeting demands for a long focal length

An engineers' sketch of a broadcasting lens design.
Designing a pro video lens that had ultra-telephoto reach in a lightweight body is one of the technical challenges overcome by Canon's R&D department.

At first it seemed like an impossible task. Meeting the focal length requirement of 1,000mm, a 20x zoom ratio, built-in extender and 4K optical capability, not to mention making a lens tough enough for broadcast environments – which can be cold, wet, dirty and rough on equipment – and getting it all under the target weight limit of 6kg was a challenging proposition. While it is possible to make a lens smaller and lighter by increasing the refraction, this degrades optical performance because suppressing chromatic aberrations gets ever harder. Simply adding more lens elements was also not an option because this would of course increase the overall weight.

Equally, a long focal length by necessity requires a larger unit – and with such a focal range, the lens movements need to be correspondingly larger in a 4K lens than in one designed for HD. Added to this, a lens designed for 4K shooting must be more precise in terms of zooming and focusing because 4K content is less forgiving in focus shift and also features a shallower depth of focus due to smaller pixels and hence a smaller circle of confusion.

The solution for the ultra-telephoto CINE-SERVO CN20x50 IAS H E1/P1 lens was using fewer lens elements in the design. At one stage in the process, the weight looked like it had crept up to 7kg. This was deemed unacceptable, so the process was started once again. It took Canon experience in lens design, as well as new solutions never used before, to achieve all of the design requirements.

Part of that process included multiple iterations of optical simulation technology, where improvements were made at each step. This has enabled the lens design team to create a lens that – despite the normal increase in aberration with increased sensor size, such as the move from 2/3-inch sensors to Super 35mm – still offers 4K optical performance with minimal aberration over the entire zoom range from the centre of the frame out to the edges. This image quality is maintained even when the 1.5x built-in extender is used. Marrying up the focus needs of both broadcast and cinema users was another challenge to be overcome, as was ensuring focus accuracy in the shallow depth of field shooting scenarios that large format cameras often provide.

As a leader in optical technology, this is the sort of challenge Canon engineers strive to meet, producing groundbreaking lenses that enhance the shooting options of cinematographers and directors and allow for new ways of shooting, whether for broadcast or cinema. Exceptional R&D, a desire to reach for the seemingly impossible, and the ability to listen to customers' requests is what keeps Canon at the forefront of lens development.

Autor: David Newton

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