1Dx Review

Started Jul 11, 2012 | Discussions thread
David Franklin
Contributing MemberPosts: 947
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Always much confusion about this much misunderstood concept
In reply to ihv, Jul 11, 2012

Bokeh is a way of defining the quality of an out-of-focus area in a picture field, and it is controlled by the lens entirely; aperture blade shape and number (creating the shape of the diaphram opening) and lens formula and construction determine bokeh.

Depth-of-field is only indirectly determined by the size of the imaging sensor or film, or the lens focal length. The factors which directly determine depth-of-field are: the exact framing of the picture field (point of view), the point of sharp focus in that picture field (focus distance) and the lens aperture itself (which is defined by the focal length of the lens as compared to the size of the diaphram opening). Whether a lens is a wide angle or telephoto or in between, except for extremely small and arcane differences, matter not a bit as to depth-of-field, except as how they change the resulting picture field for any given sensor size. And, of course, the same can be said of format size; the same focal length lens for different sensor sizes yields different picture fields when the format size is changed. No matter how you slice it, this is how it works. However, this is a very hard concept to "get" unless one sees graphic evidence for it for oneself. It helps if you shot different format sized film in the past, like 35mm and 8x10, where the differences between point of view at the same nominal focal lengths are so gross and obvious, and the differences in depth of field in trying to shoot the same picture field (with grossly different focal length lenses, which, in turn, affect the depth-of-field controlling focus distances) are also so obvious.

I hope I've explained this in a way that is fairly understandable; it's pretty hard to do without lots of illustrations and diagrams, which I am too lazy and time-limited to make.

Regards,
David
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