User: The greenhouse effect is a result of A. absorption and radiation of energy in the hydrosphere. B. consumption of fruits and vegetables that produce a biofuel. C. absorption and radiation of energy in the atmosphere.
A principal focus or focal point is a special focus: 1  For a lens, or a spherical or parabolic mirror, it is a point onto which collimated light parallel to the axis is focused. Since light can pass through a lens in either direction, a lens has two focal pointsâone on each side.
Once you are in this mode you will be able to move your focus point around your scene using either the dial or the arrow buttons to the right of your screen. If your focal point stops moving just simply press your AF point selection button again and it will start to move to your command again.