Canon Powershot A590 IS User Manual page 81

79
If the zoom is adjusted after these values are set, the
aperture value or the shutter speed may change in
accordance with the zoom position (p. 75).
The brightness of the LCD monitor matches the selected
shutter speed and aperture value. When you select a fast
shutter speed or shoot a subject that appears dark, set the
flash to (Flash on) to make the LCD monitor display
bright.