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Canon EOS 5D Review • AF & Metering

Peter Kun Frary

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Auto Focus

The EOS 5D auto focus design is a masterful balance of flexibility, speed and accuracy. Like the EOS 1V, 3, and Elan 7, the 5D uses a CMOS chip for its AF sensor, as opposed to the BASIS or Multi-BASIS chip used in older EOS cameras such as the A2 or 1N. The nine AF sensors are arranged in a pyramid shape similar to the 20D/30D:

The center AF sensor has a cross configuration and, thus, is sensitive to both horizontal and vertical lines. The center top and bottom sensors are single axis sensors sensitive to vertical lines. As such, they don't work with the AF assist patterns of the 550EX and ST-E2 (but work with the 430EX and 580EX). The remaining six AF sensors are single axis sensors sensitive to horizontal lines. Nine cross sensors would be ideal, but this design yields a good balance between horizontal and vertical sensitivity. Additionally, there are six "invisible" AF sensors clustered in the center (outlined in blue), used only for AI servo tracking and enabled via custom function.

Like 1 series bodies, the 5D enables"high-precision focus detection" with F2.8 or faster lenses. Unlike 1 series bodies, the center cross retains both vertical and horizontal sensitivity with F5.6 lenses, albeit at "normal-precision focus detection." AF is not possible with lenses slower than F5.6.

AF Sensor Selection

Individual sensors may be selected with the joystick or automatically via fuzzy logic. The advantage of this system is off-center subjects may be captured without locking focus and recomposing. AF modes include One Shot (stationary subjects), AI Servo (predictive follow focus of moving objects) and AI Focus (automatic selection of One Shot or AI Servo). To select a sensor is a two step process:

1) Press AF point selection button.

2) Fiddle with joystick to select sensor.

Custom function 13.1 invokes direct use of the joystick (multi-controller) for AF point selection without pressing the AF point selector. Pressing the AF point selector restores auto AF point selection. I find this method the fastest selection means save ECF (eye controlled focus). Unfortunately it isn't as reliable as ECF and often skips over the targeted AF point. If you prefer, you may set a custom function to use the QCD for selection. The QCD is more surefooted but slower.

There is one gotcha: it's difficult to reach the joystick while in the vertical position with a BG-E4 (battery pack/vertical release) attached. I can work the joystick with my thumb only if I use my middle or ring finger on the shutter.

Manual AF point selection functions in all exposure modes except Full Auto.

AF Sensitivity

In good light, AF is extremely fast, about the same speed as an EOS 3. As light gets dimmer, performance slows down but is respectable and easily bests the 10D, 20D and Elan 7NE. Canon specs autofocus of the Elan 10D at EV .5-18 with an EF 50 1.4 USM lens. The EOS 5D is 1 stop more sensitive at Ev -0.5-18. However, AF performance in the last few stops of sensitivity is definitely better. Even with a slow zoom, e.g., EF 24-1054L IS USM, low light AF is acceptable.

Ballys at Las Vegas • EOS 5D and EF 24-105 4L IS USM hand held. ISO 800, 1/60 second at F4 with IS engaged.

How To Improve Low Light AF

All autofocus SLR cameras share similar limitations when shooting in low light. In low light photography, it is crucial to use fast lenses and focus on points of contrast. In other words, you can't merely point 'n shoot when lighting gets dim. You must pick your targets carefully. Here are some tips for low-light photography with the EOS 5D (these tips are useful with any EOS camera):

When it is really dim (e.g., a living room lit by table lamps), it is best to use only the center cross sensor (at this point you'll need a tripod). That is, manually select the center sensor and turn off all other AF sensors. It is extremely important to lock focus on a contrasty detail, e.g., an eyebrow rather than a smooth forehead. Furthermore, low light AF is enhanced considerably by using a fast prime lens such as the EF 50 1.4 USM or EF 35 2.0, rather than a slow zoom. The increased depth of field of a wide angle lens, e.g., EF 28 2.8, also helps improve low light AF. A bright image in the viewfinder is an additional benefit of using a fast lens.

In candlelight murkiness or complete darkness, you must use the AF assist light of a Speedlite to autofocus. With a near-infrared AF assist light you may use automatic focusing point selection. It's a shame Canon omitted the built-in near-infrared AF assist light. It made low-light AF elegant and convenient on older bodies such as the A2 and Elan II. When discreetness is paramount, you may disable flash with a custom function (CF7-1) and use a Speedlite for AF assist only. Oddly, EOS 1 series lack a custom function to disable flash.

If you have good eyesight, you can still focus the old fashion way, manually! If you enjoy manual focus, consider installing the Ee-S focusing screen. Its higher contrast view (but darker) is supposed make manual focusing easier.

AI Servo

This is a great camera for weekend sport shooters. Lock on to a moving subject in AI Servo, keep the shutter pressed halfway, and the camera tracks the subject as it moves from side to side (sensor to sensor) and towards or away from you. It confirms side to side movement with red sensor flashes! Very cool. Custom function CF17-1 enables the cluster of 6 "invisible" AF sensors during AI Servo, helping insure your subject stays in focus. The EOS 5D AI Servo is much better at tracking moving objects than my 10D, 20D and Elan 7NE.

AF Problems: Too Many Choices?

With all these AF choices, how can you go wrong? Actually, you can by choosing an inappropriate operation mode for your subject or shooting style. Tyros frequently complain the EOS 5D produces blurry images. They use Full Auto and let the fuzzy logic chip select the subject. Unfortunately, it may lock AF on a shinny foreground object or a bright background rather than the intended subject.

The cure is to take control of the camera, rather than letting it control you. When auto AF point selection fails, use manual AF selection, lock-AF-recompose or manual focus. With experience, you'll learn to engage the best technique for each situation.

©Copyright 2006 by Peter Kun Frary • All Rights Reserved

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