by MC Soft Focuz
Why must I expose manually?
Using the camera's average meter makes you an average photographer.
If you use any of the camera's automatic modes (P, Av or Tv) and take individual photos of a black, a white and a gray object, they will all turn out gray.
Try it and see.
This works for most subjects because most average scenes have some black, white and gray in them. But what happens when there is white smoke, or a white bride in a white dress, or the proverbial black cat at night sitting a pile of coal? You don't want either to look gray.
Shoot manual (M). Expose for a gray card, or a mid-tone subject, eg. the back of your hand. ie. Adjust the three components of exposure—ISO, aperture and shutter speed—until the meter reads zero.
Now, without any additional adjustment, take individual photos of a black, a white and a gray object. They will turn out black, white and gray.
You are on your way to mastering exposure.