February 2013

EF24-70mm f/4L IS USM / EF35mm f/2 IS USM

 

Photo 2: EF35mm f/2 IS USM

Photo 2: EF35mm f/2 IS USM

This month's technical report presents two new EF lenses: the EF24-70mm f/4L IS USM (Photo 1) and the EF35mm f/2 IS USM (Photo 2).

I. EF24-70mm f/4L IS USM

Development objectives

We developed this standard zoom lens to be a smaller, lighter, easier-to-use, high-performance lens that rounds out the f/4L lens series. And when combined with the EOS 6D, which packs full-size camera performance into a compact, lightweight body, the EF24-70mm f/4L IS USM lens lets users enjoy comfortable high-quality photography with convenient portability anytime.

The main features of the lens are listed below.

A small, lightweight standard zoom lens belonging to the high-quality f/4L series
Contains two aspherical lens elements and two UD lens elements to deliver outstanding edge-to-edge image quality at all zoom settings
A macro switch enables macro shooting at the extreme telephoto end (max. magnification of 0.7x)
Equipped with a hybrid IS function that is effective during macro shooting
Compact design with a total length of just 93 millimeters
Robust durability that meets the demands of the digital age
Circular diaphragm provides beautiful bokeh out-of-focus effects
Well-sealed against water and dust intrusion for shooting in harsh conditions
An inner-focusing system and a ring USM provide fast, silent autofocusing
Full-time manual focus mechanism
Fluorine coating applied to the front and back lens surfaces

The following sections detail the lens's technologies.

Feature 1 - Outstanding edge-to-edge image quality at all zoom settings

Figure 1: Cross-section view of the EF24-70mm f/4L IS USM optics

Figure 1: Cross-section view of the EF24-70mm f/4L IS USM optics

The lens's optical system consists of a newly developed seven-group zoom construction. By using an inner-focusing system that focuses with the second lens group, we fashioned a small, lightweight standard zoom lens that delivers excellent image quality in a total length of just 93 millimeters.

The lens is constructed with 15 elements in 12 groups (Figure 1). The two aspherical lens elements in the second and seventh lens groups correct for various aberrations that occur when zooming. This produces consistently outstanding image quality across the entire frame at all focal lengths (Figure 2).

The design also places two UD elements in the fifth lens group, which is located just behind the aperture, to minimize axial chromatic aberrations in center of the frame as well as lateral chromatic aberrations along the edges. As a result, the lens renders high-resolution, high-contrast images with almost no color fringing at the boundary regions of subjects.

The lens coatings have also been optimized using advanced simulation technology to both drastically cut flaring and ghosting and provide excellent color balance. Furthermore, we treated the front first lens group (R1 face) and the rear lens (R2 face), which are exposed to the open air, with a fluorine coating so that dust and contamination on the lens surfaces can be wiped off easily with a dry cloth.

Figure 2: MTF characteristics of the EF24-70mm f/4L IS USM

Figure 2: MTF characteristics of the EF24-70mm f/4L IS USM

Feature 2 - True macro shooting

Figure 3: Focal length markings on the zoom ring

Figure 3: Focal length markings on the zoom ring

Figure 4: Distance scale markings

Figure 4: Distance scale markings

The No. 1 feature on this lens is the true macro shooting function that can take close-ups of tiny subjects, such as flowers and insects as well as miniature objects and accessories.

To enable macro shooting, the user pushes the macro switch lever forward and turns the zoom ring to the yellow macro range at the end of the telephoto range (Figure 3). Once the macro mode is engaged, the zoom ring can only be turned within the yellow macro range. Macro shooting is possible at magnifications*1 up to 0.7x. The focal length range is between approximately 2.3 meters and 0.2 meters (the working distance is about three centimeters) (Table 1).

When image stabilization (IS) is activated while macro shooting, the lens will automatically switch to the hybrid IS mode (see next item for details). This setting gives a stabilization gain in shutter speed of about three f-stops at a 0.5x magnification and about a 2.5 f-stop gain at a 0.7x magnification.

One important note about macro shooting is that the lens's distance scale (Figure 4) only gives distance markings for regular shooting and does not provides distance markings for macro shooting. The focus point and the available shooting range for macro shooting vary with the zoom ring movement (Table 1).

The distance scale does have a yellow line to indicate the general focus range where the image quality is good for most macro shots. (Note that the maximum magnification is about 0.5x in the distance scale's yellow line area.)

The following is an example of how to shoot so as to keep the focus position within the yellow line after autofocusing.

(1) Adjust the focus ring so that it is roughly in the center of the yellow line on the distance scale.

(2) Adjust the zoom ring and the shooting distance by moving the camera back and forth to set the magnification (i.e., the image's composition) and the approximate focus.*2

(3) Depress the shutter button halfway and shoot after the camera finishes autofocusing. If you are using a tripod, you can focus manually while watching the Live View's expanded view.

This example shows a way of macro shooting while staying within the yellow line on the distance scale where the image quality is best, as described above. However, it is not the only way to shoot. This method will also systematically minimize any image quality degradation even when the focus position is outside the yellow line's area.

*1. Magnification is the ratio between the subject's actual size and the size of its image in the image plane.
*2. If the approximate focus is too far out of focus, the camera's autofocus may shift the focus position outside the yellow line's area.

Macro position Macro 1 Macro 2
Shooting distance range 2294 - 300 mm 298 - 197 mm
Working distance 2125 - 131 mm 132 - 30 mm
Magnification 0.03x - 0.29x 0.33x - 0.7x
Field of view [mm] Approx. 764 x 1141 - 82 x 124 Approx. 73 x 110 - 35 x 52

Table 1 Macro specifications of the EF24-70mm f/4L IS USM

Feature 3 - Hybrid IS designed for macro shooting

Figure 5: Angular shake

Figure 5: Angular shake

Figure 6: Lateral shake

Figure 6: Lateral shake

The lens's image stabilizer shifts the compensating optics (the sixth lens group: G13 and G14) perpendicular to the optical axis to compensate for camera shake. When shooting normally, the image stabilizer provides a stabilization gain of approximate four f-stops in shutter speed. The image stabilizer also has a function that uses a gyro output signal to distinguish between panning and normal shooting and then automatically selects the optimal image stabilization mode for the shooting situation.

The image stabilizer operates in the Hybrid IS mode during macro shooting, as mentioned above. In addition to compensating for regular angular shake (Figure 5), caused by the camera rotating vertically or horizontally, Hybrid IS detects lateral shake (Figure 6) with respect to the optical axis with an acceleration sensor. In this way, the mode compensates for angular and lateral shake simultaneously.

Because the effect of lateral shake on the final image becomes more pronounced, even larger than the angular shake component, at greater magnifications (Figure 7), Hybrid IS compensation is particularly useful for handheld macro photography. The EF24-70mm f/4L IS USM is the second model, after the EF100mm f/2.8L Macro IS USM, to feature the Hybrid IS function.

The lens relies on an inner-focusing system and a ring USM, as well as a high-speed CPU and an optimized AF algorithm, for its AF drive. The lens offers greater AF precision because its sensor has a higher resolution than on past models.

Figure 7: Relationship between magnification and the degree of image blurring when typical camera shake occurs

Figure 7: Relationship between magnification and the degree of image blurring when typical camera shake occurs

Feature 4 - Better usability in addition to excellent reliability and durability

Figure 8: Waterproofing and dustproofing

Figure 8: Waterproofing
and dustproofing

Photo 3: EW-83L hood for the EF24-70mm f/4L IS USM

Photo 3: EW-83L hood
for the EF24-70mm f/4L IS USM

For this lens, we packed a rich feature set and high performance into a compact, lightweight body just 93 millimeters long and weighing approximately 600 grams. We also made the lens more user friendly.

Starting from the EF lens's design concepts of "the beauty of converging light and a comfortable operation feel," we pursued a simple, streamlined form suitable for an optical instrument along with a tough, but subtle construction.

Since this is an everyday zoom lens, we emphasized the visual size balance between the lens and the camera body when the lens is attached as well as the rotational feel of the rings for stress-free operability.

Like the EF24-70mm f/2.8L II USM, the barrel design gives far more reliability and durability. And waterproofing and dustproofing have been applied around all controls and moving parts so the lens can be used in similar harsh conditions (Figure 8).

A zoom ring lock lever (which also serves as the macro switch lever) has been added to prevent the zoom from extending out while carrying a strap-held camera with the lens attached. The lens comes with the petal-shaped EW-83L hood (Photo 3), which attaches with a two-pronged bayonet mount and includes its own locking mechanism. The hood's inner surface has been given a flocking treatment for excellent anti-reflective performance.

This report has primarily concentrated on the lens's macro shooting functions. It is impressive that such a compact, lightweight lens form not only has the remarkable versatility of a standard zoom lens, covering all focal lengths from portraits to landscapes, but also has true macro shooting functionality. This single lens can capture a huge variety of subjects, from city streets to nature's mountains, with all kinds of creative expressions. As such, it is the ideal lens to choose when graduating to a full-size camera such as the compact, lightweight EOS 6D body.

We encourage everyone to try to bring his or her photographic imaginings to life with this lens.

II. EF35mm f/2 IS USM

Development objectives

The EF35mm f/2 IS USM is a wide-angle prime lens that was developed as the successor to the EF35mm f/2, which has been the go-to wide-angle lens for many years. The new lens was designed to provide better image quality to meet the demands of the digital age as well as greater functionality and performance than previous models.

We completely revised the optics and mechanical construction and added faster, more accurate autofocusing, an image stabilizer unit, and a full-time manual focus mechanism, in addition to better image quality. All these features were fit inside a luxuriously designed, ergonomic body.

The main features of the lens are listed below.

A large aperture wide-angle prime lens with a f/2 optical system
A GMo aspherical lens element ensures excellent image quality
A wide-angle prime lens that comes with an image stabilizer
A ring USM provides fast autofocusing
Optimized lens placement and coatings minimize ghosting and flaring
Lens automatically detects between normal shooting and pan shooting and selects the best image stabilization mode for the shooting situation
Supports full-time manual focusing
Circular diaphragm renders beautiful bokeh out-of-focus effects

The following sections detail the lens's technologies.

Feature 1 - Excellent image quality and performance

Figure 9: Cross-section view of the EF35mm f/2 IS USM optics

Figure 9: Cross-section view of
the EF35mm f/2 IS USM optics

Like the EF24mm f/2.8 IS USM and the EF28mm f/2.8 IS USM, this lens features an image stabilizer, despite being a wide-angle prime lens. It also has the same rear-focusing system so that the overall length does not change when focusing.

The lens's construction consists of 10 elements in 8 groups (Figure 9). Placing a GMo aspherical element as the rearmost lens element compensates for various aberrations, giving consistent image quality across the entire frame and, thus, attaining better rendering performance than previous models (Figure 10).

The lens coatings have also been optimized using advanced simulation technology to both dramatically cut flaring and ghosting and provide excellent color balance.

Other improvements reduced the previous model's minimum focusing distance of 0.25 meters to 0.24 meters and raised the maximum magnification from 0.23x to 0.24x. And in addition to the highly expressive portrait shots with soft-focus backgrounds that only a large f/2 aperture lens can achieve, the eight-blade circular aperture can also create stunning bokeh out-of-focus effects.

Figure 10: MTF characteristics of the EF35mm f/2 IS USM

Figure 10: MTF characteristics of the EF35mm f/2 IS USM

Feature 2 - Outstanding image stabilization functionality and a USM

Photo 4: EW-72 hood for the EF35mm f/2 IS USM

Photo 4: EW-72 hood
for the EF35mm f/2 IS USM

This lens also has a lens-shift image stabilizer that delivers a stabilization gain of approximate four f-stops in shutter speed. It also has the same function that uses a gyro output signal to distinguish between panning and normal shooting and then automatically selects the optimal image stabilization mode for the shooting situation.

A ring USM drives the focus lens group, and a high-performance CPU and optimized AF algorithm enable fast autofocusing. Full-time manual focusing is also available, allowing the user to adjust the focus manually after autofocusing with leaving the autofocus mode (when in One-Shot AF mode).

The exterior design's concept was to create a luxurious feel for the lens while prioritizing operability. The result is a unified wide-angle prime lens design.

The lens comes packaged with the petal-shaped EW-72 hood (Photo 4), which includes a locking mechanism. The hood's inner surface has been given a flocking treatment for excellent anti-reflective performance.

With the addition of this lens, Canon has completely renewed its series of IS-enabled wide-angle prime f/2 lenses at the 24mm, 28mm, and 35mm focal lengths. Each lens has its own characteristics and advantages. We invite everyone to try them out and create memories and creative photo works.

Model EF24-70mm f/4L IS USM EF24-70mm f/2.8L II USM
Lens construction 15 elements in 12 groups 18 elements in 13 groups
Aspherical lens elements 2 3
Super UD /
UD elements
0 / 2 1 / 2
Aperture blades 9 (circular) 9 (circular)
Min. focusing distance
(macro mode)
0.38 m (0.2 m) 0.38 m
Max. magnification
(macro mode)
0.21x (0.7x) 0.21x
Filter size 77 mm 82 mm
Max. diameter 83.4 mm 88.5 mm
Length 93 mm 113 mm
Weight Approx. 600 grams Approx. 805 grams

Table 2 Specification comparison between the EF24-70mm f/4L IS USM and the EF24-70mm f/2.8L II USM

Model EF35mm f/2 IS USM EF35mm f/2
Lens construction 10 elements in 8 groups 7 elements in 5 groups
Aspherical lens elements 1 none
Aperture blades 8 (circular) 5
Image stabilizer Yes No
Min. focusing distance 0.24 m 0.25 m
Max. magnification 0.24x 0.23x
Filter size 67 mm 52 mm
Max. diameter 77.9 mm 67.4 mm
Length 62.6 mm 42.5 mm
Weight Approx. 335 grams Approx. 210 grams

Table 3 Specification comparison between the EF35mm f/2 IS USM and the EF35mm f/2