Canon's Remarkable New Lens Achieves the (Near) Impossible
It is in the nature of shooters—and human beings in general, I suppose—that we don’t like compromises. We want everything, and that demanding attitude (as unrealistic as it may be) seems to apply particularly to our lenses. For reasons of convenience and practicality, especially in the nonfiction realm, we want single lenses that do it all.
The migration of documentary, sports, and wildlife shooters to large-format single-sensor cameras has created a powerful demand for optics that somehow, in some way, re-create the can-do-everything 2/3-type experience that many of us are used to. This has posed a near-impossible challenge for lens manufacturers like Canon, who’ve never had it easy meeting the less-than-reasonable, often-conflicting demands of nonfiction shooters.
In the 1980s, shooting snowy egrets and other large birds for National Geographic, I bought a few houses and cars with the spectacular images captured with my workhorse Canon 300mm 2.8L – a revolutionary telephoto lens that offered breakthrough performance, speed, and contrast.
For sports and wildlife shooters, Canon’s new 50–1000mm T4.5 4K zoom has a similar life- and career-transforming potential.
Our demands in optics have been tough enough over the past few decades, when we employed small-format cameras almost exclusively. Shooting HD for wildlife and sports, we wanted the longest telephoto zoom we could find. Compelling close-ups tell the story, and for those of us toiling regularly in the sports and wildlife rackets, getting in close and staying there is the key to our success—and to our continuing to pay the bills. Look deep in the eyes of a ravenous lioness in Tanzania or a shifty-eyed rhesus monkey in a Mumbai slum, and audiences instantly feel the vibe and visual thrust.
At the same time, shooters operating in such uncontrolled environments also require an ample wide angle. Being able to shift focal lengths quickly is critical to capturing visually coherent stories. And we want our daily workhorse lenses to be fast, with a constant f-stop throughout the zoom range. We also want our lenses to offer good close-focus capability, feature easy-to-manipulate controls, and be compact and lightweight. Toss in a 2x extender, built-in zoom servo and a rear filter slot, and pretty soon you’re talking about some real optical complexity!
Maintaining excellent contrast to the corners Canon’s new 4K ultra zoom represents a remarkable achievement in a small and lightweight package. Many more types of low dispersion glass are used, compared to the company’s HD lenses.
The problem is that some of these demands conflict with one another. If a fast zoom is to exhibit minimal or no ramping, it necessarily requires a larger and heavier front-focus group, which works against the mandate for portability. Other trade-offs apply to the built-in extender. Yes, it allows higher magnification, typically for the price of a significant loss of contrast, resolution, and light transmission.
The demands of wildlife shooters seem simple enough at first. Given the S35mm format, most of us need a minimum 1000mm focal length for our bread-and-butter work. This stipulation stems from the common need to shoot subjects like a 1.4m gorilla (not a guerrilla!) full-frame at 100 meters, which, if you do the math, works out roughly to a 1000mm lens.
Wildlife and sports shooters often fret over the size and mass of their gear, especially the long lenses that tend to be particularly bulky and unwieldy. Serious shooters understand the best lens technology is useless if we can’t easily wrangle and transport the thing to remote locations. Humpability is a key consideration! At 6.6kg (14.5lbs) and 40.5cm (15.9 inches) in length Canon’s new ultra zoom offers much better than average humpability. Its large diameter aspheric elements help eliminate individual elements, which in turn reduces weight and mass, while improving light transmission, i.e. speed.
Of course we still have to consider the bulk and weight of a long zoom. That can be a serious shortcoming when slogging through an Amazon jungle or across the Arctic tundra on a dog sled. Those of us with many years of experience in the field know the most arduous part of the job is not necessarily the camera-shy wildlife or the penny-pinching producers. Often, it's the transporting and wrangling of all our cases of gear day-in and day-out. Especially given the hassle and expense of airline travel these days, a practical 4K/1000mm zoom lens ought not much exceed 7kg (15lbs) or 40cm (about 16 inches) in length, reasonably speaking.
These are the real constraints that Canon faced when designing its new lens, in particular the diameter of the input lens group. Canon ultimately settled on a 136mm front element, which enabled a T5 (F4.5) maximum aperture. A wider, heavier front element group could certainly have increased lens speed (and with it lens price), but the approach was deemed unacceptable given the size and weight constraints. When it comes to optics, the Canon team may be miracle workers. But even there, a few laws of physics still apply.
The size of the front elements in a zoom lens is critical. When magnification exceeds the entrance lens diameter, some light is inevitably lost as the pupil entrance diameter exceeds the physical diameter of the input lens group. The imperative to limit size and weight means that some ramping is inevitable. As shooters and more or less mature individuals, we don’t like it, but we accept some ramping and are in fact quite used to it. The Canon 50-1000 holds a constant T5 (F4.5) until 560mm, when the entrance pupil size exceeds the available real estate in the front lens group and gentle ramping begins. The lens speed slows to a still-reasonable T8.9 at 1000mm.
The slower speeds in long telephoto lenses used to pose a serious challenge to wildlife shooters in particular, who tend to work in highly variable conditions at higher than normal frames. Today, with the advent of 4K cameras like the VariCam 35 with ISO 5000 capability, the slower speed of telephoto lenses is less of an issue. It may even be advantageous by reducing the need for heavy ND filtration.
The 1.5X extender brings the maximum focal length of the new lens to 1500mm. Extreme precision is required to manufacture such a zoom with the extender while maintaining good contrast throughout the range. Note there is an approximate one stop light loss (T7.5 maximum aperture) with the extender enabled.
The extraordinary performance of Canon’s 50-1000 zoom may be attributed largely to the sophisticated coatings used to help maintain good contrast and sharpness to the corners characteristic of a true 4K objective. The uncoated lenses currently in vogue among artsy DPs produce plenty of flare with a concomitant loss of crispness, but these hobbled lenses have no place among nonfiction, wildlife, and sports shooters, whose mandate in life and business is entirely different. Canon applies at least 10 coatings per lens surface to drive down the black level and expand contrast, thus increasing light transmission or ‘speed’ substantially.
The multiple coatings target a full spectrum of wavelengths, creating a bevy of interference patterns at the glass surface that eliminate more than 99.9% of reflections and resultant flare. (By comparison, uncoated lens elements may reflect 5% or more of incident light.)
In order to meet shooters’ stringent size and weight demands, the 50-1000 required an entirely new design. While earlier ultra-zoom lenses employed four lens groups for focus, two fixed and two moving, the 50-1000 lens features fewer front elements to save weight and reduce bulk. The new lens contains only two front focus groups, one moving and one fixed, with six elements in total instead of the 10 or 11 as used previously in similar long zoom optics.
Originally introduced in Canon’s 7–17mm zoom, the 50–1000mm features an integrated Cine Servo drive that covers the full range of the zoom in 1.5 seconds. This feature is especially relevant to TV and broadcast folks. Standard zoom and focus controllers may be used to connect to the 3x 20-pin ports provided.
For Canon and other lens makers, such significant advances can be traced to a much more sophisticated optical simulator. The lack of chromatic aberrations in the 50-1000mm, and the absence of breathing of focus through the zoom range, required Canon to design and produce several key elements with an aspheric surface.
One such surface is used in the front focus group to eliminate multiple individual elements, which reduces overall weight and bulk while improving lens speed. Additional aspheric surfaces are used in the zoom’s variator group, which compensates for aberrations introduced in the focus group.
Such complexity in optics is not for the faint of heart. But then neither are the many contradicting demands we shooters are making on the world’s lens makers. As more of us adopt S35mm 4K capture as the new norm, we are going to need more impossible 4K optics—like Canon’s 50-1000—to enable it.