Correct Over / Under Exposure

Modern digital Slr’s have very sophisticated metering systems that work very well in many situations but there are some situations that will result in a underexposure (to dark) or overexposure (to light) image. If you understand why this happens you will be able to correct it at the time of taking the image which is preferable to trying to adjust the lighting / exposure later in a photo software editing programme like Photoshop.

Digital cameras work on the principle that the image you are taking has a mid-tone or 18% grey which most images have, but where there is a predominately white or dark image it will try and get as close to a 18% grey as it can, metering it as a mid-tone image. The result is a dark or black image that will be too bright and overexposed and a bright or predominately light image that is underexposed or to dark.

How to Correct Over / Under Exposure? There is a couple of ways to correct under or overexposure. You can bracket your exposure so that the camera will take a number of images in increments of a 1/2 or 1/3 stop over and under the correct exposure the camera is telling you it should be, many digital cameras will do this automatically if you set it up. Your best friend here is your histogram if you see the graph bunched to the left or right and not spread over the whole graph the chances are your image is over or under exposed. If the image looks too bright dial in a (-) 1EV, 1.3EV, 2 EV, in exposure compensation to reduce the amount of light reaching the sensor. If your image is to dark dial in a (+) number in exposure compensation to increase the light reaching the sensor. It is important to use your histogram graph/image to determine how much (-) or (+) compensation you require. Use your histogram and get used to seeing images presented in this way and you will quickly see if you have a well exposed image or not. Many digital cameras allow you to switch to different metering from multi-zone, spot metering etc… this can be useful so that the camera can meters from the area of interest rather than taking an average of the entire image, this can be useful where you have many different / opposite lighting conditions, this will tell your camera where you want the exposure reading to be taken from.

Best of luck.