New firmware, new features for the EOS-1D X

Firmware updates are not what they used to be, certainly getting more sophisticated!

Canon has updated the firmware for the 1Dx camera to allow it autofocus with lenses that have a maximum aperture of f/8. Originally the camera could only autofocus if the lens had a maximum aperture of f5.6, this was a departure for 1 series cameras and left many wildlife photographers VERY disappointed, because it stopped people  from using the 100-400 f4.5-5.6 lens with a 1.4 tele extender (or the 800 with the 1.4 if you have one) and the 500mm f/4 with my 2 x tele extender. Canon has solved that issue. For more info on the firmware update click here.

Read the article about the firmware here

Autofocus down to f/8 at the center AF point

Initially, for technical reasons, the EOS-1D X allowed AF with any lens or lens + Canon tele extender combination that provided a maximum aperture of f/5.6 or faster (f/4, f/2.8, etc.). This has nothing to do with the actual aperture you may want to shoot a picture at – the AF system doesn't care if you shoot a picture at f/2.8 or f/32. Its only concern is that the maximum aperture of an attached lens or lens + extender is sufficient to allow all the pixels on the AF array's line sensors to be used.

However, many nature, wildlife, sports and other shooters who frequently combine lenses like the 500mm or 600mm f/4L lenses with 2x tele extenders, or f/5.6 lenses (such as the 100-400mm f/4.5-5.6L IS, 400mm f/5.6L, or 800mm f/5.6L IS) with the 1.4x extender, made strong requests to allow some form of autofocus operation with extenders in place. Again, Canon's engineers have both listened and responded in a timely fashion, with firmware upgrade v. 1.1.1.

Lenses and Tele Extenders compatible for f/8 AF operation

With Canon-brand tele extenders, whether they're the current Version III models, or previous version I or II extenders, AF will be possible with the following lenses with EOS-1D X cameras for cross-type coverage at the center AF point, if the camera's firmware is version 1.1.1 or higher:

With EF 1.4x:

• EF 100-400mm f/4.5-5.6L IS
• EF 400mm f/5.6L
• EF 800mm f/5.6L IS
• all other f/4 or faster Canon EF lenses, compatible with Canon tele extenders

With EF 2.0x:

• EF 70-200mm f/4L and 70-200mm f/4L IS
• EF 300mm f/4L IS
• EF 400mm f/4L DO IS
• EF 500mm f/4L IS and 500mm f/4L IS II
• EF 600mm f/4L IS and 600mm f/4L IS II
• all other EF lenses, f/2.8 or faster, compatible with Canon tele extenders

Keep in mind that only select Canon EF lenses are officially compatible with Canon's EF tele extenders. Simply stated, these are:

• All Canon 70-200mm L-series zooms, f/2.8 or f/4
• Canon EF 100-400mm f/4.5-5.6L IS
• All fixed focal length L-series lenses, 135mm or longer
• Canon EF 400mm f/4 DO IS

Other Canon EF and EF-S lenses are not designed to have Canon tele extenders attached to them.