Program AE mode is quick and easy because you can leave it to the camera to figure out the best combination of shutter speed and aperture. But sometimes you’ve got specific settings in mind, such as a small aperture for more depth of field, or a fast shutter speed to freeze movement.
The usual advice is to swap to aperture-priority or shutter-priority mode and choose the setting you want here – but there is a quicker way.
Still in program AE mode and with the exposure meter still active (half-press the shutter release if you need to re-activate it), just turn the rear command dial. Turning it to the right shifts the aperture/shutter speed combination towards faster shutter speeds, turning it to the left shifts the combinations towards smaller lens apertures.
You wouldn’t use this if you wanted to take a whole series of shots at specific shutter speeds or lens apertures, but for single shots it’s quicker than changing modes.