Depth of field question

Started 7 months ago | Discussions thread
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zenpmd
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Depth of field question
7 months ago

I am a bit confused about portrait lenses. In particular comparing the DoF of an 85 and a 135. My question is simple, but the answer may be complex.

If I have exactly the same framing, ie, a human head filling the exact same portion of the frame, and if I have set the apeture of each lens the same so as to have the front of the nose and the back of the ear in focus, will the amount of background blur also be the same?

To use a worked example, I assume it is possible for two lenses to have both the nose and ears in focus, because each lens, has say 2ft of "field", yet one of the lenses loses focus after say only another 1 ft whereas the other loses it only after 3 more feet.?

The reason for this question is that I see shots on the internet with massive out of focus backgrounds, but a lot in focus on the person, whereas, for example, if I try to get a lovely out of focus amount where I obliterate the background with my D5200, I cannot also get my dogs nose in focus, so I am wondering if using, say a 300mm lens would do this whereas a 85mm cannot? Any help much appreciated!

 zenpmd's gear list:zenpmd's gear list
Sony Alpha 7S Sony FE 35mm F2.8 Sony FE 55mm F1.8
Nikon D5200
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