单反相机镜头的参数各有什么含义？
怎样根据用途不同来选购不同参数的镜头？
推荐回答（4个）
会问这个问题 应该是初学者 我就用最通俗的话 给你简单说说吧
有两个比较常用的参数：焦距 光圈
焦距，焦距一般用MM（毫米）位单位 主要影像拍摄视角的大小
135相机就是我们常见的单反 已50MM为标准镜头因为这个焦距的视野于我们单眼看到的范围接近
焦距 数值越小 代表可以拍摄的角度越广 越大 低于 50MM 的镜头也称之为广角镜头
焦距 数值越大 代表可以拍摄的角度越小 越远 高于 50MM 的镜头也称之为中长焦镜头
光圈，的单位用英文F表示 影像单位时间的曝光量 通俗的说光圈越大 就可以在越暗的环境下拍照 适用的场景更多
光圈的大小表示方法为 数值越小光圈越大 比如 F2的光圈是大于 F8的
根据根据不同的途径选镜头
比较常规的方法是
拍风景、大场景 用 广角镜头
拍摄人像 或者无法走进的主体 用中长焦
如果不希望拍摄的问题变形严重 可以使用 50MM的标准镜头
请举例说明，什么参数
F2.8 说明镜头是固定光圈的。
F3.5-5.6 说明镜头是可变光圈的。
35MM 说明镜头是固定焦距35MM 用在全画幅机身上是小广角镜头。
50MM 说明镜头是固定焦距50MM，用在全画幅机身上是标准定焦镜头。
200MM 说明镜头是固定焦距200MM，用在全画幅机身上是长焦镜头。
18-200MM 说明镜头是变焦镜头，从广角到长焦都可变。
如果这些镜头用在APS-C机身上，焦距要X系数。佳能机X1.6 ，尼康，索尼，宾得机X1.5
如果是旅游机，要求轻松，方便，那么配有广角大变焦的比如18-200，16-85 等。
如果拍微距，要专门的微距镜头，固定焦距，60MM，90MM，100MM的。通常放大比是1:1
如果专门照人像，那么用70-150 的定焦效果好。
如果是体育记者，拍动物，鸟类，那么可能用70-200MM，300MM，500MM 固定光圈的。
镜头上还有一些不重要的标志，比如，是超声波马达的，是特殊镀膜的，是特殊光学玻璃的等。
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