Canon EOS Rebel T6i EF-S 18-55mm IS STM Lens Kit Instruction Manual - Page 124

g: Changing the ISO Speed to Suit the LightK ISO [AUTO] If the ISO speed is set to [AUTO], the actual ISO speed setting will be displayed when you press the shutter button halfway. As indicated below, the ISO speed will be set automatically to suit the shooting mode. Shooting Mode ISO Speed Setting No Flash With Flash A/7/C/2/4/5 ISO 100 - ISO 6400 3 C/P/x/6/G 8 F d/s/f/a ISO 100 - ISO 1600 ISO 100 - ISO 6400 ISO 100 - ISO 12800 ISO 100 - ISO 6400*1 ISO 400*2 (Except in the A, C, 6, and F modes.) With bulb exposures ISO 400 *1: Depends on the maximum ISO speed limit set (p.123). *2: (1) If fill flash results in overexposure, ISO 100 or a higher ISO speed will be set. (2) In the C, 2, 3, 4, 5, x, P, and modes, if you use bounce flash with an external Speedlite, the ISO speed will be automatically set within ISO 400 - ISO 1600 (or up to the maximum limit). When [AUTO] is set, the ISO speed is indicated in whole-stop increments. However, the ISO speed is actually set in finer increments. Therefore, in the image's shooting information (p.306), you may find an ISO speed such as ISO 125 or ISO 640 displayed as the ISO speed. 124