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.
The other side to focusing concerns which points or areas are used to achieve focus. This is less straightforward, since the options provided vary considerably between models. Above: Even some compact cameras have a collection of focusing controls. A camera will typically use an auto-area/all-points option by default.