Chuck Westfall is the technical advisor at the Professional Engineering & Solutions Division, Canon U.S.A. Inc. In the following interview Chuck explains major technical features of the new EOS 5D Mark III, the latest full-frame Digital SLR from Canon with a 23 Million-pixel CMOS image sensor.

AH: The current AF system in EOS 1D Mark IV delivers excellent performance when photographing subjects like birds in flight against a varied background. In this case photographer often uses center point with a fixed number of expansion points, as opposed to color-tracking or automatic AF point/area selection given the erratic nature of the subject. What benefits does the new system bring in terms of speed and precision in this application?


CW: The number and distribution of high-precision cross-type AF points has increased on the new 61-point AF system relative to the 45-point AF system used by the EOS-1D Mark IV. Moreover:

 The overall AF system speed of the EOS-1D X including lens drive is superior to that of the EOS-1D Mark IV on a lens for lens basis. The overall AF detection speed of the EOS 5D Mark III is superior to the AF detection speed of the EOS-1D Mark IV.

 The level of AF precision for 5 of the central area AF points on the 61-point sensor (i.e., the dual X-shaped cross-type points) is superior to the level of precision for any of the AF points on the 1D Mark IV.

 21 cross-type AF points in the central area of the 61-point sensor are functional with maximum apertures as small as f/5.6; None (zero) of the cross-type points on the EOS-1D Mark IV are functional as cross-type sensors at maximum apertures smaller than f/4.

 The 61-point AF sensor has twice the low light sensitivity as the 1D Mark IVís 45-point AF sensor (EV -2 vs. EV -1).

 The 61-point AF system supports AI Servo III, which is superior in subject tracking stability and consistency compared to AI Servo II found on the EOS-1D Mark IV.

 The 61-point AF system adds a greater degree of user control for subjects with various characteristics of acceleration and deceleration such as birds in flight.

 The 61-point AF system not only has 16 more AF points than any of the 45-point systems, it is also 20% wider in coverage (19mm vs. 15mm), making it easier for photographers to keep their subjects within the active AF area.


AH: We understand due to the large number of cross-type and double-precision cross-type sensors there was not enough room to fit the f/8 line sensor in the new AF sensor. However for wildlife applications the 2X Tele-extender in combination with f/4 super-telephoto lenses offers great flexibility. Is it possible for Canon to address this issue?


CW: This request has been conveyed for consideration.


AH: In practice the EOS 1D Mark IV AF system was superior to that of the EOS 7D in AI-servo with both f/4 and f/5.6 lenses despite having fewer cross-type sensors. How important are the cross-type sensors in AI-servo performance for a fast moving subject?


CW: Cross-type AF points increase the percentage of readable subject contrasts compared to single-axis sensors, but there are many other factors to consider when comparing overall AF system performance.


AH: Is it possible to toggle between the single/expansion/zone AF modes in 5D Mark III with the M-fn button in the same manner as the EOS 7D?


CW: Yes. On both cameras, you press the focusing point selection button first, then press the M.Fn button to change the AF point selection mode. Both cameras support Spot AF with all compatible lenses, Single Point AF, Selected point plus 4 adjacent points, Zone AF, and Automatic Focusing Point Selection using all AF points. However, because it has 61 AF points instead of 19, the EOS 5D Mark III also supports ďSelected point plus 8 adjacent pointsĒ in addition to ďSelected point plus 4 adjacent points.Ē













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AH: We understand AF settings is vastly different between the EOS 5D Mark III/1DX and the previous EOS 1D Mark IV system. In addition to the presets tuned for a particular subject is it possible to adjust parameters such as AI-servo tracking sensitivity similar to the 1D MKIV?


CW: Yes.


AH: What is the combined shutter lag plus mirror blackout time in the EOS 5D Mark III?


CW: Shutter lag time is 59 milliseconds, the same as the EOS 7D, and considerably faster than the EOS 5D Mark IIís 73 milliseconds. Viewfinder blackout time is 112 milliseconds on the EOS 5D Mark III vs. 145 milliseconds on the EOS 5D Mark II.


AH: Given the increased burst speed why doesnít the 5D Mark III support class 10 SD-UHS cards?


CW: The EOS 5D Mark III supports Class 10 SDXC and SDHC memory cards, but not the UHS standard.


AH: Increase of burst speed from 4fps to 6fps is significant and welcome, however, it still not adequate for some applications. Is Canon going to develop an 8fps or faster compact professional camera in near future or is that feature exclusive to the 1DX?


CW: no comment on Canonís future plans or products.







AH: The EOS 5D Mark II was considered the benchmark of overall image quality in the Canon lineup. Apart from improvements in noise reduction by DIGIC5+ processor, what improvements has Canon made to the CMOS image sensor itself relative to the 5D Mark II?


CW: Three main areas of image quality-related improvement on the EOS 5D Mark III image sensor compared to the EOS 5D Mark II are:

 Gapless Microlenses: This feature increases the amount of light received by each photodiode compared to the gapped microlenses used on the 5D Mark IIís image sensor.

 New Photodiode Structure: The photoelectric conversion rate of each photodiode has been improved.

 On-Chip Noise Reduction: Canonís proprietary technology in this area, which was first shown on the EOS D30 Digital SLR in the year 2000, has steadily improved over the years.

The net result of these improvements is a cleaner signal at all comparable ISO speeds for the 5D Mark III, as well as increased sensitivity that is indicated by the expansion of the standard ISO range from 6400 on the 5D Mark II to 25,600 on the 5D Mark III.

We also doubled the throughput speed of image data from the CMOS sensor to the rest of the image processing chain by increasing the number of simultaneous readout channels from 4 to 8. This change has a side effect of helping to improve EOS Movie quality as well by cutting the level of rolling shutter artifacts in half.

EOS 5D Mark III Full-Frame CMOS Image sensor with 22 million pixels

AH: Canon has indicated two stops improvement in high ISO performance relative to the 5D Mark II. We understand this figure refers to in-camera JPEG files with noise reduction. Approximately how much of an improvement in high ISO performance or low ISO dynamic range is expected in RAW (CR2) files when using the latest Canon DPP software?


CW: These figures are not being disclosed, but of course they will be lower than the noise reduction achieved with in-camera JPEGs and EOS Movies.


AH: The EOS 5D Mark II offered a significant improvement in resolution over the original EOS 5D. What guided Canon in their decision to stay with 22 million pixels unlike the previous scaling trend?


CW: Staying in the 22 megapixel range allowed us to maximize base level image quality, while at the same time enabling us to achieve a maximum continuous shooting speed of 6 frames per second. This is the fastest continuous shooting speed in the 20+ megapixel full-frame sensor DSLR category, and it expands the potential customer base for the EOS 5D Mark III by making it more attractive to photojournalists and entry-level sports photographers.

AH: A 22-Mpixel sensor is great. However, there are photographers who can benefit from even a higher resolution sensor, such as wildlife photographers who cannot physically get closer to their subject and can benefit from flexibility in cropping. Does Canon intend to develop a higher resolution full-frame sensor in near future?


CW: no comment on Canonís future plans or products.


AH: What new improvements are offered in the new Canon DPP software in combination with EOS 5D Mark III?


CW: We targeted three new features for the new version of DPP that will be released together with the EOS 5D Mark III:

 Support for the 5D Mark IIIís HDR mode.

 Support for the Multiple Exposure mode of the 5D Mark III and EOS-1D X.

 A new feature called Digital Lens Optimizer processes RAW images to achieve ideal optical characteristics for all types of optical aberration or diffraction, effects of a low-pass filter in front of a CMOS sensor, etc. This function improves image quality particularly in the image periphery in addition to the image center. This function is made possible because the entire design-through-manufacture process, for camera, CMOS sensor, EF lens, and DPP, is carried out entirely at Canon. Images are processed optimally using lens information in the image files (focal length, subject distance, and aperture) and lens data specially for the Digital Lens Optimizer. (However, the size of a .CR2 file will be two to three times larger after applying the Digital Lens Optimizer.) Adjustments are made for such aspects as spherical aberration, chromatic aberration, astigmatism, curvature of field, sagittal halo, chromatic aberration of magnification, axial chromatic aberration, diffraction, and the effects of a low-pass filter in front of the CMOS sensor. DPPís Digital Lens Optimizer will be usable with any of 29 compatible lenses initially. It works with .CR2 files from EOS models released since 2006 (EOS 30D and forward).


AH: Are there any differences in hardware or software between the EOS 5D MKIII and EOS 1DX AF modules?


CW: The AF sensor and AI Servo III tracking algorithms are identical for both cameras. However, the EOS 5D Mark III uses a 63-zone Dual Layer iFCL sensor for exposure metering whereas the EOS-1D X uses an approximately 100,000 pixel RGB sensor powered by a DIGIC 4 processor for exposure metering. As a result, the EOS-1D X supports EOS iTR AF (Intelligent Tracking and Recognition) that can apply face and color detection data from the 100,000 pixel sensor for improved subject tracking when the camera is set for automatic focusing point selection. In addition, the EOS-1D X achieves a higher lens motor drive speed with select L-series USM telephoto lenses than the 5D Mark III because of the 1D Xís more powerful battery pack.

EOS 5D Mark III Auto Focus module