Understand yo ur histo grams
Discover why the brightness histogram takes the heat out of manual exposures
USING spot metering and the exposure indicator in the viewfinder, you can set the exposure based on a
specific part of the scene. But the histogram shows you the exposure for the whole image. By reviewing the histogram after you’ve taken a shot (or checking the live histogram, if available), you can see whether you’re making full use of the camera’s imaging sensor and if any areas are going to lose detail. Remember that the histogram is based on a JPEG version of the image and the camera settings made at the time; if you shoot raw, then you’ll have more headroom to fine-tune the exposure with compensation later, when you process the shot.
As indicated on the previous page, you can’t use exposure compensation in Manual mode, although some cameras let you do so when you use Auto ISO. This is because in Auto ISO, the camera will change the ISO to ensure that the aperture and shutter speed that you’ve dialled in deliver what it determines to be a good exposure; changing the aperture or shutter speed to increase or decrease the exposure will simply result in the camera altering the ISO to compensate for the change you made! To make the image brighter or darker, you need an option to dial in exposure compensation.