How to Get Proper Exposure With Canon SLR Cameras

The exposure of a picture refers to how much light impacts the sensor or film strip. An overexposed photo will appear washed out, while an underexposed photo will be very dark. To control exposure with a Canon SLR camera, you manipulate aperture, shutter speed and ISO. By adjusting these three settings, you can attain the proper exposure for just about any shot.

Things You'll Need

• Single-lens reflex camera

Instructions

1. Determine the priority of your settings: aperture, shutter speed and ISO. If you want a shallow depth of field, the aperture needs to be wide open. If you are trying to freeze a high-speed event such as an auto race, shutter speed needs to be high. If you simply cannot have any grain, ISO needs to be low. Whichever setting ranks as most crucial, set that one first and adjust the others to meet its needs. Do steps two through four in order of importance.

2. Aperture: The shallower the depth of field, the wider the aperture needs to be. If you want the camera to focus in on one subject while slightly blurring everything else so your chosen subject stands out, set the aperture as wide as possible, which means the lowest number, such as 2.8 or less. Each time the aperture widens one step, such as going from 4.0 to 2.8, the shutter speed needs to double to compensate or the ISO needs to be cut in half.

3. Shutter speed: During the day, shutter speeds will usually range between 1/250th and 1/1000th of a second. However, if you are shooting a very fast event such as auto racing, you will want to set the shutter speed as fast as possible, which is usually 1/4000th or 1/8000th of a second. To achieve this, set the aperture to its widest value and increase the ISO.

4. ISO: ISO stands for International Standards Organization and refers to the sensitivity to light of the pixels when the picture is taken. One hundred is the standard for low sensitivity, and there will be no graininess at this level. Each time the ISO doubles, such as going from 400 to 800, the shutter speed must double to compensate or the aperture must go down by one step, and there will be more grain in the picture.

5. If you are using a digital camera, take a test shot and look at the histogram by reviewing the photo on the camera and clicking the "Info" button. The histogram is the graph of what colors are being produced. If the histogram has a high concentration on the left, chances are the photo is underexposed. The aperture needs to be widened, the shutter speed needs to be slowed, or the ISO needs to be increased. If the histogram has a high concentration on the right, the photo is likely overexposed. This can be fixed by closing the aperture, increasing the shutter speed or decreasing the ISO.

6. Retake the shot and check the histogram. Make small adjustments and continue to retest your settings until you have an exposure you are happy with.

Tips & Warnings

• If you are taking a picture with vastly different light conditions between your subject and the background, consider using spot metering. Spot metering, often available as a menu option on digital cameras, takes the exposure based on a small area of the picture rather than the average of the entire picture. For example, if you were taking a picture of two people in front of a sunset, you would want the two people to be exposed correctly. Using spot metering in the two individuals would set the camera to properly expose them rather than having them be very underexposed because of the bright back light.

• The camera's automatic metering tool can be confused by different intensities of light in different areas of the picture. Pick the parts that are most important, such as a person's face, and know that properly exposing that part of the photo might mean another part, such as the sky, may be over- or under-exposed.

References

• Achieving Correct Exposure
• Spot Metering