Canon EOS Rebel T6i EF-S 18-55mm IS STM Lens Kit Instruction Manual - Page 122

g: Changing the ISO Speed to Suit the LightK Set the ISO speed (image sensor's sensitivity to light) to suit the ambient light level. In Basic Zone modes, the ISO speed is set automatically (p.124). 1 Press the button (9). 2 Set the ISO speed.  While looking in the viewfinder or at the LCD monitor, press the keys or turn the dial to select the desired ISO speed, then press .  Select [AUTO] to set the ISO speed automatically (p.124). ISO Speed Guide ISO Speed Shooting Situation (No flash) Flash Range ISO 100 - ISO 400 Sunny outdoors The higher the ISO ISO 400 - ISO 1600 Overcast skies or evening time speed, the farther the flash range will extend ISO 1600 - ISO 12800, H Dark indoors or night (p.166). * High ISO speeds will result in grainier images. Under [54: Custom Functions (C.Fn)], if [2: ISO expansion] is set to [1: On], "H" (equivalent to ISO 25600) can also be selected (p.338).  Under [54: Custom Functions (C.Fn)], if [3: Highlight tone priority] is set to [1: Enable], ISO 100 and "H" (equivalent to ISO 25600) cannot be selected (p.339).  Shooting in high temperatures may result in images that look grainier. Long exposures can also cause irregular colors in the image. 122