Canon EOS 5D Mark III Instruction Manual (en)

Troubleshooting Guide
If the card’s writing speed is slow, movie shooting may stop 
automatically. When the compression method is set to [IPB], use a CF 
card with a reading/writing speed of at least 10 MB per sec., and a SD 
card with a reading/writing speed of at least 6 MB per sec. When the 
compression method is set to [ALL-I (I-only)], use a CF card with a 
reading/writing speed of at least 30 MB per sec., and a SD card with a 
reading/writing speed of at least 20 MB per sec. To find out the card’s 
reading/writing speed, refer to the card manufacturer’s Web site (p.219).
If the movie shooting time reaches 29 min. 59 sec., the movie shooting 
will stop automatically.
If the shooting mode is <
A/d/s/f/F>, the ISO speed will be set 
automatically. In the <a> mode, you can freely set the ISO speed (p.226).
Under [z2: ISO speed range], if you set the [ISO speed range]’s 
[Maximum] setting to [25600/H], the maximum ISO speed for manual ISO 
speed setting will be expanded and then ISO 16000/20000/25600 can be set. 
However, since shooting a movie at ISO 16000/20000/256000 may result in 
much noise, it is designated as an expanded ISO speed (displayed as [H]).
If you shoot a movie when [Maximum: 25600] is set with [ISO speed range
and ISO speed is set to ISO 16000/20000/25600, the ISO speed will switch to 
ISO12800 (during movie shooting with manual exposure). Even if you switch 
back to still photo shooting, the ISO speed will not revert to the original setting.
If you shoot a movie when 1. L (50) or 2. H1 (51200)/H2 (102400) is set, the 
ISO speed setting will switch to 1. ISO 100 or 2.  H (25600) respectively 
(during movie shooting with manual exposure). Even if you switch back to 
still photo shooting, the ISO speed will not revert to the original setting.
Movie shooting terminates by itself.
The ISO speed cannot be set for movie shooting.
ISO 16000/20000/25600 cannot be set for movie shooting.
The manually set ISO speed changes when switching to 
movie shooting.