Concept of development
The EF-S17-55mm f/2.8 IS USM (Photo 1) is a large aperture, high-performance standard zoom lens with a maximum aperture of f/2.8. It was developed to bolster the lineup of dedicated interchangeable lenses for EOS DIGITAL cameras using APS-C size digital imaging elements (EOS 30D, EOS 20D, EOS 20Da, EOS Kiss Digital N and EOS Kiss Digital as of May 2006).
The development concept is as follows:
Large aperture with maximum aperture of f/2.8
High image definition throughout the entire zoom range
Image stabilization equal to about three shutter speeds
Digital camera compatibility
Feature 1: Large aperture with maximum aperture of f/2.8
The optical system of the EF-S17-55mm f/2.8 IS USM is designed to provide a large aperture, high definition and image stabilization. The optical design takes advantage of the smaller image circle and shorter back focus of EF-S lenses optimized for APS-C size digital imaging elements, enabling a large f/2.8 maximum aperture while keeping the optical system compact.
It has inner focusing by the second lens group and parallel shift-lens image stabilization by the twelfth and thirteenth lens groups (image stabilizer lens group) (Fig. 1).
The focal length is equivalent to 27-88mm in full-frame 35mm format.
Feature 2: Ultrahigh image quality
The optical system of 19 elements in 12 groups uses three precision aspherical lenses of two types, which helps minimize aberrations that occur during zooming and focusing, enabling the large f/2.8 maximum aperture and high definition throughout the entire zoom range.
Two UD lenses are used to minimize chromatic aberrations throughout the zoom range, providing L-series excellent quality images with both high resolution and contrast throughout the zoom and focusing ranges (Fig. 2).
Fig. 2 MTF Characteristic Charts of EF-S17-55mm f/2.8 IS USM
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Feature 3: Image stabilization of about three shutter speeds
Through the use of a dedicated high-performance compact image stabilization (IS) unit (Photo 3), developed specifically for the EF-S17-55mm f/2.8 IS USM, and a vibration gyro for precise camera shake detection, it gives image stabilization equivalent to using a shutter speed about three steps faster (Fig. 3).
The general rule for the slowest permissable shutter speed to avoid camera shake is 1/focal length in seconds, or for the APS-C format, 1/(focal lengthx1.6) in seconds so the slowest acceptable shutter speed for 17mm focal length is about 1/30 seconds. Using the image stablizer, good images can be obtained at a rate of 90% or over even at 1/8sec.
Furthermore, the f/2.8 maximum aperture allows a fast shutter speed, thus hand-held shooting is possible even in low light (Photo 4, 5).
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| Photo 4 Image stabilizer ON | Photo 5 Image stabilizer OFF |
The image stabilizer used in the EF-S17-55mm f/2.8 IS USM also has the following excellent features.
• The image stabilizer is activated within half a second after pressing the shutter button halfway, allowing the user to capture the decisive moment.
• The same image stabilizer effects can be attained when using a monopod as in hand-held shooting.
• There are no restrictions on using a tripod.
Feature 4: Lens coating optimized for use with digital SLR cameras
The EF-S17-55mm f/2.8 IS USM optical design and coating optimized for use with digital SLR cameras gives both good color balance and minimizes ghost and flare attributable to surface reflections from the digital imaging element.
Feature 5: Superb operability
Closest focusing distance of 0.35 meters
The 0.35 meter minimum focusing distance throughout the zoom range is achieved by increasing the power of the focusing lens group. The maximum magnification is 0.17x at 55mm (field of view: 88 x 131mm).
Circular aperture for attractive bokeh effects
Thanks to the EMD's (electromagnetic diaphragm) circular aperture, the lens provides attractive blur effects (bokeh).
Silent, high-speed AF
In addition to the silent ring-type ultrasonic motor (USM) and inner focusing, the high-speed CPU and optimized AF algorithm contribute to very fast autofocus.
Manual focusing enabled even in AF mode
The EF-S17-55mm f/2.8 IS USM has full-time mechanical manual focusing that allows manual focus after one-shot AF operation without leaving AF mode.
Switch design that prevents unintended switching
The focus mode switch and IS switch are designed to prevent unintended switching during shooting or when being carried.
Non-rotating filter ring
Since the filter does not rotate while zooming or focusing, circular PL (polarizing) filters are easy to use.
Use of the Canon 77mm PL-CII filter is recommended to prevent vignetting.
Dedicated large scalloped hood with superb light blocking
The EW-83J, a large scalloped hood dedicated to the EF-S17-55mm f/2.8 IS USM, has superior antireflection flocking on the inner surface. It is very effective in keeping unwanted light out of the lens (Photo 6).
Feature 6: Environmentally friendly design
The optical system contains only environmentally friendly lead-free glasses.
Effective from July 2006, EU (European Union) will restrict the use of certain hazardous substances* in the electrical and electronic equipment according to the ''EU's Restrictions on Hazardous Substances (RoHS) Directive''.
The EF-S17-55mm f/2.8 IS USM is already in compliance with Canon's own standard covering the RoHS directives including those still being finalized.
*Six substances: lead, mercury, cadmium, hexavalent chromium, bromine flame retardant PBB (polybrominated biphenyl), and PBDE (polybrominated diphenyl ether).
Medium telephoto L-series lens with an ultra-large aperture of f/1.2 and increased AF speed
Concept of development
The EF85mm f/1.2L II USM (Photo 2) is an L-series medium telephoto lens developed as a successor to the EF85mm f/1.2L USM, which is very popular for its ultra-large aperture of f/1.2 and high resolution since it was released in 1989.
The model has been redesigned to increase AF speed, while retaining the excellent optical performance of its predecessor.
The development concept is as follows:
Inheriting excellent optical performance of the original EF85mm f/1.2L USM
Much higher AF speed than its predecessor
Use of circular aperture
Feature 1: Inheriting excellent optical performance
By adopting a large aperture, precision ground and polished glass aspherical lens with the same 8 elements in 7 groups as its predecessor, the EF85mm f/1.2L II USM minimizes aberrations such as spherical aberration and provides excellent quality images with both high resolution and contrast from the maximum aperture of f/1.2 (Fig. 4).
The lens uses relative floating element construction in which the rear lens group is fixed and the other groups extend as a unit during focusing. This suppresses aberration variations and achieves excellent performance over the entire imaging area (Fig. 5).
Feature 2: Much higher-speed AF
The combination of a front lens group focusing system in which groups 1 to 7 are extended and a ring-type USM drive is the same as its predecessor, but the AF speed has been significantly improved by up to 1.8 times* compared to its predecessor through the use of a high-speed CPU and optimization of AF algorithms.
* Depends on camera and shooting conditions.
Feature 3: Circular aperture for attractive bokeh effects
Thanks to the EMD's circular aperture together with the shallow depth of field typical of a large aperture lens, the lens provides attractive blur effects (bokeh).
Feature 4: Lens coating optimized for use with digital SLR cameras
Like its predecessor, the EF85mm f/1.2L II USM uses coating optimized for use with digital SLR cameras. As a result, it successfully realizes both good color balance and minimization of ghost and flare attributable to surface reflections from the digital imaging element.
Feature 5: Superb operability
Focusing ring providing a smooth feel to operation
The electronic lens ring system provides subtlely smooth focusing. It also provides full-time manual focusing that allows manual focus after one-shot AF operation without leaving AF mode.
Distance information for improving flash exposure precision
Distance information can be sent to the camera during AF, thus making the EF85mm f/1.2L II USM compatible with the E-TTL II autoflash system for the optimal flash exposure.
Rubber coating for excellent grip
A soft rubberized outer coating has been used to provide a more secure grip and easier handling.
Dedicated hood with superb light blocking
Like its predecessor, the EF85mm f/1.2L II USM uses the ES-79II cylindrical hood, which is excellent for preventing reflection thanks to flocking on the inner surface.
Feature 6: Environmentally friendly design
The optical system contains only environmentally friendly lead-free glasses. The EF85mm f/1.2L II USM is also in compliance with Canon's own standard covering the RoHS Directive.
The issue of the Technical Report introduces the two high-performance lenses.
Table 1 and 2 show the major specifications and data on use with the extension tube.