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.
Top of the line, professional cameras can have 45 to 51 focus points (although really only 11 -19 are selectable, the rest are assist points). There are two types of focus points, single plane and cross point. Single plane only work on lines of contrast perpendicular (at a 90 degree angle) to their orientation.