Canon EOS 1DS MARK II 9443A009 Instruction Manual (en)

For vertical shooting, the vertical grip (camera bottom) has a shutter 
button, Main Dial, AF point selection button, AE lock button, Assist 
button, and FE lock/multi-spot metering button. 
Before using the vertical grip controls, 
turn on the vertical-grip on/off switch. 
When you are not using the vertical 
grip, be sure to turn off the vertical-grip  
on/off switch to prevent inadvertent 
operation of the vertical grip controls. 
Vertical Shooting