Canon 1DX Autofocus Review Part III - Firmware 2.0.3
Improved Low Light AF Capability
This is an 'under the hood' change and one that doesn't require any photographer input. Essentially the AI Servo tracking has been enhanced to apparently improve AF in low light situations. I haven't noticed any difference.
AI Servo 2nd Image Priority or More Simply How Do You Want the Camera to React after the first image has been taken?
The scale of setting has been increased to a -2 (speed priority) to +2 (focus priority) thereby allowing subtle changes to be made depending on the shooting circumstances. Selecting -2 is telling the camera to release the shutter even if AF is not acquired. Press photographers are bound to find this useful but I've set my 1DX to +2. Out of focus images are no use to me so if the AF needs a little more time to acquire before the shutter is released that isn't a problem.
Accel/Decel AF Settings Changed or "Is your subject going to be moving at a consistent speed, or will it suddenly stop or accelerate"?
I had previously written about my interpretation of this function and that when it was originally released Canon's explanation would have benefited from additional examples. They've improved it (to some degree) with this Firmware release. AI Servo is designed for subjects that move at a constant pace without erratic movement thereby allowing the AF to predict where the subject will be. Setting this function to 0 achieves this. For subjects that suddenly start or stop moving, or accelerate / decelerate quickly, changing this function to +1 or +2 "tells" the camera to expect such changes.
A good example is a long jumper who is going to accelerate from a standing start, jump and then quickly stop. Clearly, this isn't consistent movement and an ideal case for moving to +1, or +2. Ice Hockey players would be another example. The -1 and -2 settings are new and frankly confusing.
When I first read their purpose I immediately thought it was performing what Tracking Sensitivity claims to achieve. Canon state that Tracking Sensitivity reacts to sudden and major changes in what the camera sees, whereas a negative setting on Accel/Decel resists minor but sudden changes close to the subject. Trying to fully understand how major and minor are defined and what near to the subject means need further clarification - they seem remarkably similar functions. Some testing is required to understand what the subtlety is between this negative setting and negative (locked on) Tracking Sensitivity.
Improved Auto ISO Functionality - Exposure compensation in Manual Mode
Prior to Firmware 2 if one of Shutter Speed, Aperture or Auto ISO was changed, the other was changed to retain a correct, manual exposure. Now with Auto ISO engaged exposure compensation can be dialled in, the shutter speed and aperture remain unchanged but if the lighting changes the Auto ISO will fluctuate. This is a really useful feature and one I immediately introduced into my workflow.
Garry Ridsdale Feb 2014.