The Canon 40D is a prosumer level camera (a camera that blends professional features with consumer features like optimized scene-shooting modes) with a 10 megapixel sensor and the ability to shoot 6.5 frames per second. Its low-light performance is not as good at high ISOs, but the speed, combined with the 10 megapixel sensor, makes the 40D a good camera for action shots, especially in well-lit arenas. While the 40D has an "Auto" mode, photographers will get better results shooting in "Manual".
Depth-of-field
Depth-of-field is controlled via aperture. With the 40D in "Manual" mode, you can adjust the aperture and the shutter speed. First, turn the "Mode Control" dial on the top left of the camera to "M".
The 40D has two control jog dials for use in "Manual" mode, one at the top right of the camera behind the shutter button, called the "Main Control Dial", and one on the right side of the LCD screen on the back of the camera, called the "Quick Control Dial". Jog dials are small wheels that you can rotate quickly to choose different settings. Look through the viewfinder and rotate the "Quick Control Dial". You will be able to see the aperture setting change as you rotate the dial.
Depth-of-field refers to how much of the image is in focus. Large depth-of-field is achieved via high aperture settings of f/11 or more, while shallow depth-of-field, used to blur out the background and highlight just one part of a scene, is achieved by low aperture settings of f/2.8 to f/3.5.
Shutter speed
Shutter speed is used to stop motion. Faster shutter speeds let you freeze faster moving objects without blurring the image, while slow shutter speeds can be used to create more artistic images like stars moving against a night sky. With the camera "Mode" in "M", rotate the "Main Control Dial" to change the shutter speed. As you look through the viewfinder you will see the shutter speed displayed.
Exposure
Aperture and shutter speed work together to create a proper exposure. Aperture affects depth-of-field by controlling how much light hits the sensor. Lower aperture settings mean more light hits the sensor and higher aperture settings reduce the amount of light let let in. For any given exposure, the lower the aperture setting, the higher you can set the shutter speed and still get a proper exposure.
The 40D has an "Exposure Index" that you can see both in the viewfinder and on the LCD screen when shooting in "Manual" mode. The "Exposure Index" is a linear graph with four squares. When the "Exposure Index" is to the left, the image is underexposed. To the right, it is overexposed. Adjust your shutter and aperture settings to get the "Exposure Index" indicator centered for a proper exposure.
ISO
ISO (International Organization of Standardization), a holdover term from the film days which used to be referred to as ASA (American Standards Association), is the sensitivity of the sensor to light. In "Manual" mode, ISO also needs to be set in the camera. Higher ISOs enable you to set higher apertures and shutter speeds for a given exposure setting. However, higher ISOs also result in greater amounts of noise in the image. With the 40D, the highest functional ISO setting is 1600, though a boost to 3200 is available for exceptionally low light at a significant cost to image quality.
To set ISO speed, press and hold down the "ISO" button on the top right of the camera, behind the "Main Control Dial," and rotate the "Main Control Dial" to scroll through to the ISO setting you want. This will be displayed on the small LCD screen on the top of the camera behind the ISO button. When you get to the ISO speed you want, let go of the "ISO" button.
Tags: aperture settings, shutter speed, Control Dial, Exposure Index, Main Control, Main Control Dial