Before I discuss this issue more, let me describe what I mean by manual exposure. Three basic elements combine to produce a well-exposed image. Aperture (the lens opening which controls the amount of light entering the camera), shutter speed (which controls how long that light is exposed to the sensor or film), and ISO (the setting that controls how sensitive the sensor is to the incoming light).
We photographers take pride in our knowledge of how cameras work. We also enjoy knowing how aperture affects the image and how shutter speed affects the image. We fill our brains with all the "technical" aspects of photography. Most of us also try to learn about design, composition, color, sharpness and blur to impact the "art" of photography.
The trick is to balance the use of both and handle the "realities" of taking photographs. How much time do you have? How capable are you of hiking, climbing, bending? How much endurance do you have? Can you afford to reach the most exciting, beautiful, seldom-seen places or things? What kind of camera equipment can you afford? How much equipment can you carry? How is your vision? How much risk are you willing to take in dangerous or potentially dangerous situations?
It is pretty clear that many factors affect how you take and present photographs. Exposing the image is one of those factors. Modern cameras have a fully automatic setting, where the camera sets the ISO, shutter speed and aperture for you. Cameras that cost $300.00 or more do a very good job in this fully automatic setting.
Cameras also have an aperture mode, where you set the aperture you want to use and the camera then applies the proper shutter speed. This is usually called "A" or "Av". These cameras also have a shutter speed mode, where you set the shutter speed and the camera applies the proper aperture.
Modern cameras include a fully manual mode, usually called "M". This allows you to set both the aperture and shutter speed you want to use to capture the image.
I do not entirely agree that manual exposure is required to create great photographs. In fact, you can take a bad photograph with manual settings, just as you can take a bad photograph with automated settings. I use some form of automated settings for 90% of the photographs I take. Perhaps the aperture mode is the best one for the largest number of shooting situations. However, I do agree that ISO settings must be your own judgement - using auto ISO is not the best way to assure well-exposed photographs. I will discuss setting ISO in another blog.