Understanding EOS Autofocus: The EOS 1D Mk IV

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EOS 1D Mark IV autofocus array

Up until the release of the EOS 1D-X the EOS 1D Mark IV was Canon’s most advanced professional camera. Photographers who bought one will use it happily for many years to come. Some readers may also be tempted to buy one on the second hand market, as a relatively economical way of purchasing a 1 Series camera.

The EOS 1D Mark IV has a 45 point autofocus (AF) array with up to 41 cross-type AF sensors, depending on the lens used with the camera. This is the same array used by all 1 Series cameras up until the EOS 1D-X (which you can read about here).

1 Series cameras

EOS 1D Mark IV camera

Before I look at the autofocus of the EOS 1D Mark IV in more detail (pictured above), let’s take a brief look at the 1 Series range of EOS cameras. These are aimed at professional photographers and are designed to withstand the rigours of the working professional’s life. These are some of the features that differentiate 1 Series camera from other EOS cameras:

  • Weatherproofing. 1 Series cameras are more resistant to water and dust, especially when used with L series lenses (that are also weatherproofed).
  • Build quality. 1 Series cameras are built to last. A disadvantage of this is that they are heavier than other EOS cameras.
  • Built-in portrait grip. No need to buy a portrait grip. The built-in grip on 1 Series cameras houses a larger battery that lasts longer.
  • More shutter actuations. The shutters are built to last longer than those on other EOS cameras.
  • More AF points. Up until the release of the EOS 7D if you wanted an EOS camera with more than nine AF points you had to buy a 1 Series camera. Now, you also have the choice of the EOS 7D, 5D Mark III and (to a lesser extent with 11 AF points) the 6D.

Up until the release of the EOS 1D-X, 1 Series EOS cameras were split into two lines:

The 1D series

EOS 1D, 1D Mark II, 1D Mark IIN, 1D Mark III, 1D Mark IV

These cameras have an APS-H sensor (mid-way in size between APS-C and full-frame sensors). They have high burst speeds, high precision autofocus and are aimed at wildlife and sports photographers.

The 1Ds series

EOS 1Ds, 1Ds Mark II, 1Ds Mark III

These cameras have full-frame sensors and higher megapixel counts than their 1D counterparts. The ‘s’ stands for studio, which is where these cameras are intended to be used. They have slower burst speeds. The autofocus system is exactly the same as the corresponding 1D series camera.

The 1D-X

Last year, the 1D and 1Ds lines were consolidated into the 1D-X, an all-rounder with a full-frame sensor, high burst speed and high-precision 61 point autofocus.

EOS 1D Mark IV

This is the autofocus array of the EOS 1D Mark IV:

EOS 1D Mark IV AF points

If you manually select an AF point (the best way to use the camera in One Shot AF mode), there are 39 high precision cross-type AF points to choose from if you have a lens with an aperture of f2.8 or wider. This also applies to some L series lenses and lens/extender combinations with a maximum aperture of f4 (listed in the camera’s instruction manual):

EOS 1D Mark IV cross-type AF points

If you let the camera select an AF point automatically there are 19 high precision cross-type sensors available when you use a lens with a maximum aperture of f2.8 or more:

EOS 1D Mark IV AF points

If your lens has a maximum aperture between f4 and f2.8, the only cross-type autofocus point is the centre one. If your lens has a maximum aperture of f5.6 then there are no cross-type AF sensors available.

The EOS 1D Mark IV has more cross-type AF points than preceding 1 Series cameras. These are the AF points arrays from earlier models (cross-type AF sensors available with f2.8 or greater lenses). All these cameras have 45 total AF points:

EOS 1D Mark III & 1Ds Mark III

19 cross-type AF points:

EOS 1D Mark III autofocus points

EOS 1D, 1D Mark II, 1D Mark IIN, 1Ds, 1Ds Mark II

7 cross-type AF points:

EOS 1D Mark II autofocus points


The EOS 1D Mark IV may be a discontinued model but it’s still a high-performance camera with advanced autofocus designed for sports and wildlife photographers. The autofocus of a second-hand 1D Mark IV will outperform that of any EOS camera except the EOS 5D Mark III or 1D-X. The extra ‘reach’ created by the 1.3x crop factor of the APS-H sensor may also appeal to photographers using telephoto lenses, and gives it a slight edge over full-frame cameras in some scenarios.

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