Along with the introduction of the Canon EOS 80D camera, Canon engineers are introducing an updated version of the popular EF-S 18–135mm f/3.5–5.6 IS lens. The headline feature of this lens is a completely new type of Ultrasonic motor technology, called Nano USM. We’ll concentrate on the Nano USM in this article, but will give some basic info about the new lens as well.
And until now, that has indeed been a challenge for Canon’s engineers. The simple fact is this: in most situations, what constitutes good AF performance in a lens differs significantly for still image shooting and for video:
• For still images, users normally want fast, brisk drive speed that can start almost instantly, stop on a proverbial dime, and of course accurately put the sharpest focus where the user wanted it when it does stop
• For video recording, that same fast drive usually results in a very jarring, unnatural viewing experience… video shooting usually requires smooth, consistent drive speed, without sudden starts and stops
This sounds simple, but AF motors originally designed for superior AF performance during still image shooting — like Canon’s highly-regarded ring-type Ultrasonic Motors — tended to have less than ideal smoothness when asked to perform video-oriented AF. Canon engineers developed “STM” (Stepping Motor) AF technology and applied it to drive mechanisms within recent Canon EF and especially EF-S lenses in recent years. STM focus motors indeed provided that smooth and consistent ability to drive the lens during actual video recording. And, their speed during still-image shooting was adequate for many applications.
Still, as user demands for increased video recording performance with each new generation of digital SLR camera have continued, Canon engineers recognized another approach was needed.
In the new-for-2016 EF-S 18–135mm f/3.5–5.6 IS USM lens, Canon introduces a new answer to this challenge. Using the same principles of ultrasonic vibration converted into movement, Canon engineers have developed a direct-drive system that’s incredibly compact, easily placed within the body of a lens, and has tremendous AF performance.
Nano USM gets its name from the incredibly compact size of this motor. (The name has nothing directly to do with the type of vibrational energy it generates to drive a lens’s focus elements.) In this initial application, the motor itself is small enough to fit on the first joint of a model’s finger, as we see here:
AF speed during still-image shooting rivals what users have come to expect from high-end lenses with Canon’s powerful ring-type USMs. It’s brisk and nearly instantaneous — an almost perfect match for the new AF system in the EOS 80D. Most users will doubtless agree that it’s a clear step forward from what we’ve come to expect in affordable lens focus, whether we’re referring to the previous Micro USM focus motors used in many such lenses, or the recent STM versions.
But this lens focus system is outstanding in video applications. AF operation during video recording has tremendous smoothness, and is remarkably free from the visually jarring start-stop focus movement sometimes seen with other lens focus motor systems. Another huge factor in video shooting is that the AF operation is nearly silent — very important if a microphone is attached to the camera, and vital if using the camera’s built-in microphone. Nano USM matches the relative silence of previous STM designs when focus occurs during video recording.
So it’s the combination of focus characteristics, blending the conflicting requirements of good, fast AF during stills with smooth, controllable AF during video, that makes Canon’s Nano USM such an interesting and compelling possibility for many Canon EOS photographers.
Even with this exciting new focus drive technology, for optimum smoothness during video recording, a camera body using either Canon’s Hybrid AF system, or (even better!) Canon’s Dual Pixel CMOS AF, is going to be needed, along with this new lens.
Cameras with these video focus technologies, as of February 2016, are:
• EOS Rebel T4i (650D)
• EOS Rebel T5i (700D)
• EOS Rebel T6i (750D); EOS Rebel T6s (760D)
• EOS 70D (Dual Pixel CMOS AF)
• EOS 80D (Dual Pixel CMOS AF)
• EOS 7D Mark II (Dual Pixel CMOS AF)
• EOS M; EOS M2; EOS M3; EOS M10 (with Mount Adapter EF–EOS M)
This isn’t an engineering document, and Canon’s designers have provided only basic information to date. But in general, the principle is the same as in previous Ultrasonic motor designs — but of course it’s applied differently.
Canon’s existing large, ring-type Ultrasonic motors provide a good starting point for understanding the new Nano USM's operation. Ring-type USMs actually consist of two separate metal rings, held together via spring pressure. One ring has a smooth contact surface, the other has specially designed “teeth” that touch the opposite ring. When specific types of voltage are sent to the stator (ring with teeth), it not only vibrates, but flexes in a controllable, travelling wave fashion. Contact against the smooth ring causes that ring rotate, at controlled speed, in the opposite direction of the traveling wave.
With the new Nano USM lenses, the movement in the form of vibrations is generated by sending current at very precise levels to a flat ceramic voltage element, attached to the underside of the motor pictured in this article. The long strip that forms the base of the Nano USM is actually a flexible elastic metal body. Two different types of vibrations can be generated, depending on the current applied, and the combination of these causes the entire elastic metal body to expand and contract at very precise rates, and in two distinct directions. With the round protrusions pressed against a metal slider, this movement results in linear — not rotational — movement within the lens. The actual lens elements which move for focus are driven by a rack, with guide bars to control its forward/rearward movement.
The first application of Canon’s Nano USM technology is in the EF-S 18–135mm f/3.5–5.6 IS USM lens. This lens will be combined with the new EOS 80D camera if it’s purchased in “kit” form in many markets, as well as being a lens that Canon users can step up to independently if they so desire.
Here are a few important facts about this new 18–135mm lens:
• Optical design, including use of one UD (Ultra-low Dispersion) glass element and one Aspherical element, is exactly the same as the previous EF-S 18–135mm STM lens
• Minimum focus is identical (15.3 inches; 0.39m), as is maximum close-up magnification when zoomed to the 135mm position (0.28x)
• Noticeably faster AF: lens drive speeds of the focus elements in the lens from minimum focus distance to infinity are up to 2.5x faster at wide zoom settings, and up to 4.3x faster at tele zoom settings, in tests performed by Canon engineers (vs. previous 18–135mm STM lens)
• Image Stabilization is improved in the new lens: up to 4 stops of shake-correction, allowing hand-holding at shutter speeds up to 4 stops lower than would otherwise be possible without stabilization (the previous STM version provided IS with up to 3.5 stops correction). Like the previous STM lens, this lens provides Dynamic IS at wide angle settings, providing added shake resistance during walking and similar situations while video is recorded.
• The new Nano USM version of this lens is compatible with the optional Canon Power Zoom Adapter PZ-E1; this adapter (as of February, 2016) cannot be attached to other Canon EF or EF-M lenses
• As with the STM version, this new USM lens uses electronic manual focus control, meaning the camera must be awake and active for manual focus to happen when the lens’s focus ring is turned. Manual focus is possible with the lens in One-Shot AF mode, after AF has been completed, if the user keeps his or her finger on the focus activation button on the camera. If the camera’s back-button AF is active (via Custom Function), manual focus can occur while the camera is awake, even in AI Servo AF.
• An important note about the variable f/3.5–5.6 maximum aperture of this lens: as with all EF and EF-S lenses having variable apertures, the effective aperture changing and altering light transmission during zooming will only occur at apertures wider than f/5.6. Once the lens is stopped to f/5.6 or smaller (f/8, f/11, etc.), the electronic diaphragm is able to adjust as the lens is zoomed, preserving consistent light transmission, even in Manual exposure mode.
• As with all Canon EF-S lenses, this lens is limited to compatible Canon EOS camera bodies with APS-C size image sensors, which can accept EF-S lenses. It is not compatible with full-frame EOS digital SLRs.
• This lens is not compatible with Canon’s EF 1.4x or 2x tele extenders
In its present form, Canon engineers stress that Nano USM technology gives them a very practical answer to the aforementioned challenges of fast still-image AF, while allowing great controllability and smoothness for Live View and especially video recording.
And, as shown below, it fits beautifully into the form factor of this compact lens. In this illustration, the Nano USM sits above the highlighted lens group, which is actually driven to focus the lens:
But for now, at least, it’s optimized for lens designs where the elements moved for focus are small and lightweight in size. The inner focus system of the EF-S 18–135mm f/3.5–5.6 IS design lends itself to this, with an optical system where a very lightweight element group is moved. Larger, heavier focusing elements remain better-served by the more powerful ring-type USM design, as seen in many of Canon’s mid-range EF lenses, and of course in many high-end L-series lenses as well.
Nano USM is an exciting new technology, and Canon expects it to be a great match for video content creators as well as still-image shooters using recent APS-C sensor EOS cameras. For now, however, Canon engineers have not tipped their hand as to if, and where, we might see this technology repeated in future products.
In summary, this new extended-range EF-S standard zoom lens (its coverage is approximately equivalent to a 28–200mm lens, on a full-frame camera) looks ready to be a terrific choice for the still and video shooter. And that applies to not only newcomers to digital SLRs, but experienced and seasoned users of cameras up to and including the EOS 7D Mark II as well.
The CDLC contributors are compensated spokespersons and actual users of the Canon products that they promote.
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