| 摘要 |
PURPOSE:To focus the virtual image on a face to be projected, which is formed with an auxiliary lens, onto a projection face with a main lens system by changing the distance between the auxiliary lens system and the face to be projected. CONSTITUTION:A virtual image 2' due to an auxiliary lens 4 is formed as an image O'A' near a face 2 to be projected because the distance between the lens 4 and the face to be projected is short, and this image is hardly different from an image OA; and when this image is focused on a projection face 1 by a main lens system 3, an image O''B is obtained. When the lens 4 is brought far from the face 2, the virtual image of the face 2 due to the lens 4 is formed apart from the face 2, and the size of an image O'C' is considerably larger than that of an image OC on the face to be projected. When the position of the system 3 is changed to focus the image O'C' onto the face 1, an image O''D is obtained. The size of an image OB is approximately equal to that of the image O''D, and a part OC on the face to be projected can be projected onto the face 1 with a larger size as the result. A field angle alpha of the system 3 is not especially extended, and a just generally designed lens system can be used as the system 3, and the cost is reduced considerably. |
