Wednesday, May 4, 2011

Multi-point AF

Image produced by the lens is projected, through the arrangement of mirrors, an additional sensor (or several dies) dedicated to focusing. On this matrix are separate areas are arranged so as to cover the entire frame "seen" to postpone the lens.Depending on the sophistication of a digital camera model, these areas can be from several to several dozen. Canon EOS-1D Mark IV is the 45 Each of these areas, popularly known as the point, though this is an area of ​​specific dimensions, serves to focus on him for a portion of the projected image.Focusing is based on such a draw position of the moving lens in the lens to get the greatest contrast. In contrast, a simple apparatus is selected relative vertical edges visible in the frame. Hence, known fault CDs that can not set the focus to the boat on the water, where lines of different areas of the frame are horizontal contrast. In the case of the EOS-1D Mark IV, but many other SLR cameras and the contrast is determined by the vertical and horizontal lines. Called a "cross" area. Of the 45 areas the designation field 39 is a cross areas. Focus is on
capturing an image incident on a point (area) measurementsetting the contrast for the image, which is part of the whole frame projected on the main matrixadjustment of moving lens elementsdetermine whether the contrast has improved or deterioratedwhere the contrast has improved, rules, setting the lens is repeated in the same directionif the contrast worsened, adjust the lens is "the opposite" direction.this method, step by step, we select the greatest contrast, namely setting the lens gives the best focus for the objects seen in the measuring area.Such wyzaczenie focus requires intensive computation and high-speed transfers of lenses in the lens. Calculation of designating a separate processor performs the focus, in case of the EOS-1D Mark IV is 40 MHz, 32-bit RISC on the structure. These calculations are spomagane by the main camera processor - 40 MHz, 32-bit RISC too.