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.
Point of Focus and Depth of Field. When a photographer uses the term point of focus, he is referring to that object in a photograph at which he wants to draw the most attention. Focus itself refers to the amount of the image that is sharp. Both the point of focus and the amount of focus affect the resulting image. In short, altering each one changes the look of the final photograph. In these two images, the point of focus was the same, the coneflower. However, the amount of the photo in focus, or the amount of sharpness, also called depth of field, is different. Let's deal with these subjects one at a time.