Almost all the camera today have the histogram.  The histogram is a graph that shows you the brightness of an image.  The left side of the histogram show how many “dark” pixels you have captured and the right side, how many “bright” pixels you have captured.

The region where most of the brightness values are present is called the tonal range.  Tonal range can vary drastically from image to image, you need to develop an intuition for how the numbers map to the actual brightness values.  There is no one “ideal histogram” which all images should try to mimic, histograms should merely be representative of the tonal range in the scene and what the photographer wants.

Here are some example of picture that have what some photographer called “bad exposure” because the histogram are almost completely in the left side of the histogram or the right side.  But the picture have a good exposure, the only difference are the amount of black or white pixel in the frame.  That why you need to get used to the way the histogram show the information in conjunction with the picture on the LCD to determine if you have a good or bad exposure.

In this picture most of the histogram is on the left side, but is for the dark background, the subject is well exposed.

In this one the lens flare make the histogram shift to the right. I like the result.

In the histogram if you have either of the side with a lot pixel like the last picture you may have some clipping pixel.  That means that you have pure white or pure black, with no detail.  If you look the first histogram, you can see that int the left side we almost touch the border of the histogram, but since we don’t have clipping pixel all the black in the picture have some sort of detail.  In the second, we have clipping pixel in the white side, you can see the pure white in the center of the flare that don’t have any detail, just white.

As you can see there are no correct histogram, it’s a combination of the picture in the LCD of the camera and the histogram, to determine if you have a good exposure.  Practice using it and soon it will be one of the tool you are going to use the most.

Now go out and shoot!