Canon EOS Rebel T4i 18-135mm IS STM Lens Kit Instruction Manual page 85

Shooting Tips
Change the ISO speed or use the built-in flash.
To match the subject and ambient lighting level, you can change the
ISO speed (p.90) or use the built-in flash (p.104). In the <d> mode,
the built-in flash will not fire automatically. So under low light, press
the <I> (flash) button to raise the built-in flash.
The program can be shifted. (Program shift)
After pressing the shutter button halfway, turn the <6> dial to
change the shutter speed and aperture setting combination
(program). Program shift is canceled automatically after the picture
is taken. Program shift is not possible with flash.
Differences Between <d> and <A> (Scene Intelligent Auto)
In the <A> mode, many functions such the AF operation and built-in flash
are set automatically to prevent spoiled shots. The functions you can
change are limited. Whereas with <d> mode, only the shutter speed and
aperture are set automatically. You can freely set the AF operation, built-in
flash, and other functions (p.310).
If the "30"" shutter speed and the maximum aperture
blink, it indicates underexposure. Increase the ISO
speed or use flash.
If the "4000" shutter speed and the minimum aperture
blink, it indicates overexposure. Decrease the ISO
speed.
d: Program AE
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