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目前,国内市场上出售的照相机遮光罩主要有圆柱形、圆台形和方形三种,但这三种遮光罩的遮光效果并不是最好的。在摄影中,底片上包括的景物角度是指水平方向或垂直方向的角度,并不是底片画幅对角线的角度。底片相对的两边实际包括的景物角度叫视场角,水平方向的角度叫水平视场角,垂直方向的角度叫垂直视场角（图1所示）。根据这个原理可知,最理想的遮光罩应该是矩形遮光罩（图2所示）。矩形遮光罩与传统的圆形和方形遮光罩相比,提高了防眩光能力。
At present, there are mainly three kinds of camera hoods sold in the domestic market, such as a cylindrical shape, a round shape and a square shape. However, the light-shielding effects of the three types of light-shielding hoods are not the best. In photography, the angle of the scene included in the film refers to the horizontal or vertical angle, not the diagonal angle of the negative frame. The opposite sides of the film actually include the scene point of view angle of view, the horizontal angle is the horizontal angle of view, the vertical angle is called the vertical angle of view (Figure 1). According to this principle, the best sunshade should be a rectangular sunshade (Figure 2). Rectangular masks improve the anti-glare ability compared to traditional round and square masks.