最近看了一部关于吉姆?弗雷泽镜头的纪录片，描述此镜头有极大的景深，可以同时对焦极远和极近的物体，想具体了解一下这种镜头到底是如何做到的。

超景深百万像素的视频监控镜头

…昏过去。

你们能认真的把专利看完么，答案不都在那里了

The primary lens is a very wide-angle lens...it has a very large depth of field...throws a wide image circle...on a pellicle element (which takes the normal place of film or a
sensor) ...This second lens can zoom in on the projected wide-angle image, giving an apparently longer focal length ...

他使用了一个具有较大成像圆的大广角镜头，将「具有较大景深」的影像投影在一张薄膜上，然后再用一个变焦镜头去捕捉薄膜上的影像，来实现变焦并控制光圈。

这道理简单到不能再简单，因为前面的广角镜头完成了3D-&>2D的投影转换，接下来的变焦实质是对一个2D平面的翻拍，所以不存在景深的问题。通过后面变焦镜头的「放大」，也可以获得类似长焦的效果，但由于是对2D影像的放大，所以景深没问题。

至于 @jonny lee 提到的棱镜，专利里也说了：

There is also a system of prisms in the system that allows the lens to be aimed without altering the cameras orientation.

就是为了在不变换机位的情况下让镜头可以指向别处，同景深没什么关系

不是我说的轻巧，原文就是这么表述的，「Theres nothing too very special or revolutionary about that.」，「By itself, that has also been done before,」，「Again, thats not novel in itself.」
同看了这个纪律片，感觉很震撼，潜在的价值太大了。

翻墙搜到的一段回答：

The detailed explanation is available in the patent (US5727236), which is available at Google Patents, among other places.

A simplified explanation is that he developed a system that uses two lenses. The primary lens is a very wide-angle lens, and like all wide-angle lenses, it has a very large depth of field for any given aperture (and the aperture is kept fairly large in Fraziers design). Thats what gives the deep-focus "magic"; a very wide-angle lens. Theres nothing too very special or revolutionary about that.

This particular wide-angle lens, though, also throws a wide image circle. In other words, it makes a very big picture for its focal length. Again, nothing spectacular there; covering a large film frame with a short focal length lens is something optical designers have been doing for quite some time.

The image that the wide-angle lens throws isnt used directly by the camera, though. Its focused on a pellicle element (which takes the normal place of film or a sensor) and viewed through a separate lens behind the wide-angle lens. This second lens can zoom in on the projected wide-angle image, giving an apparently longer focal length and allowing the aperture to be varied as necessary for photography/filming exposure while maintaining essentially the "baked-in" depth of field of the primary wide-angle lens. By itself, that has also been done before, as explained in the "prior art" section of the patent.

There is also a system of prisms in the system that allows the lens to be aimed without altering the cameras orientation. That part of the system is not too very different from an adjustable periscope. Again, thats not novel in itself.

Its the entire system taken together — using a large image circle from a very wide angle lens at an optimal wide aperture for that lens, taking a picture of that lenss picture through a separate lens, and having a system for articulating and orienting the two-lens system — that was patentable and award-winning. (However, it seems he blew the patent protection, at least in some jurisdictions, by poor choice of promotional methods. See the Wikipedia article for more details and links.)

我猜测是运用光学折射公式趋向极限区域的特性运用，直白说：如何让有一定角差的两根光线射入界面同一点，透过的两根折射线的角差越小，也就实现了聚焦的物像点的间距缩小，再对物像放大成像，每个透镜都要遵循以上规律

刚看了纪录片，的确感到震撼。

应用到安保监控系统，景深范围可以达到200米。。。。。。

我试了一下，即使用一个超广角镜头，也不可能获得一个大光圈的大景深照片。而且，从透镜的远离来看，透镜只有一个焦点，离开焦点以外的图像必然会不清晰。所以不存在什么3d转2d就会清晰的事情。既然2d本身不清晰，再怎么去用变焦拍，也不会清晰。那么弗雷泽产生如此大景深的镜头都是怎么弄出来的？困惑
这个节目我也看了，后来想了想觉得应该是先用一个大景深的镜头把近距离和远距离的物体成像于像面，然后用景深小的镜头拍这个像面的特写，这样应该可行吧？
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