是我没说清楚。。。。。。 看这里: http://www.lonestardigital.com/aperture_diffraction_limits.htm |
俺脚得,衍射现象无论好坏,大小镜头都会发生,是由光圈大小决定的,所以胶片和数码没有区别。有人说,小DC没有太小的光圈,一般只到F8,是由于再小就有衍射现象。但是一般F11衍射不会太严重。看画册,好多照片远近通吃,都清楚的一塌糊涂,而画质并不差。翻拍一张,已经不那么清楚了,只是说明问题。 |
Aperture area The amount of light captured by a lens is proportional to the area of the aperture, equal to: Where f is focal length and N is the f-number. The focal length value is not required when comparing two lenses of the same focal length; a value of 1 can be used instead, and the other factors can be dropped as well, leaving area proportion to the reciprocal square of the f-number N. If two cameras of different format sizes and focal lengths have the same angle of view, and the same aperture area, they gather the same amount of light from the scene. The relative focal-plane illuminance, however, depends only on the f-number N, independent of the focal length, so is less in the camera with the larger format, longer focal length, and higher f-number. This assumes both lenses have identical transmissivity. |
大头指出的对,光圈f数是焦距和物理光圈直径之比。同样的f数,因为焦距短,小DC的进光量要比SLR少的多,所以绝对清晰度也会差。 |
综上所述:f值越大越好,因为你可以两档之后还可以获得“清晰”的结果。小光圈那头就不算了,因为f32也不会影响镜头的价钱。 我打算寻摸一个f1.2~f32的50mm头,这样可用的范围是f1.8~f11。 |
小黑屋|手机版|Archiver|四海人民公摄 - 海外华人摄影爱好者网站
GMT+8, 2024-4-20 12:38
Powered by Discuz! X3.5
Copyright © 2001-2023 Tencent Cloud.