If you’re in the middle of a shoot, you can check the histogram on your camera’s LCD screen or in your viewfinder. Make adjustments if you’re surprised to find any of the following:
Left side run-off.
If you see high-frequency tones or peaks running off the left side of your histogram, that means your blacks are being clipped, and your camera is not picking up all of the shadow detail that it might. This type of “low-key” image might be what you’re going for, but if it isn’t, you can let in more light by lowering the shutter speed, widening the aperture, or raising the ISO (light sensitivity) of your camera. Each of these fixes can reduce the image quality, but you can experiment with slight adjustments to all three to get the combination of brightness and sharpness that you want.
Right side run-off.
If your image is “high-key,” you might expect peaks on the right side of the histogram. But if those peaks are cut off at the right edge, the image may be overexposed, meaning the highlight detail is washed out. In this case, take a shorter exposure, narrow your aperture, or lower the ISO to reduce the light your camera is capturing.
A bunched-up histogram.
If all your tones are packed into one area of your histogram, and there’s a lot of space on either side, the contrast may be too low. If you’re shooting in a controlled environment, you can add light to intensify highlights and deepen shadows. If the environment is out of your control, try reframing your photo to include contrasting elements or plan to adjust contrast in post-processing.