To adjust shutter speed manually while letting the camera select aperture for optimal exposure, set aperture to A and use the shutter speed dial.
S will appear in the display.
If AUTO is displayed in red, press a function button (by default, Fn2/AUTO) to exit auto mode.
At settings other than 180X, shutter speed can also be adjusted in increments of 1/3 EV by rotating the command dial. Shutter speed can be adjusted even while the shutter button is pressed halfway.
For information on the role of the command dial when the camera is used with lenses not equipped with an aperture ring, see "Lenses with No Aperture Rings".
If the correct exposure can not be achieved at the selected shutter speed, aperture will be displayed in red when the shutter button is pressed halfway. Adjust shutter speed until the correct exposure is achieved.
If the subject is outside the metering range of the camera, the aperture display will show “---”.