Focal length, framing, aperture and dof calculation question

Started Jul 20, 2012 | Discussions thread
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Albert Ang
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Focal length, framing, aperture and dof calculation question
Jul 20, 2012

Supposed that I want to get a head-and-shoulder portrait photo and I shoot using the new Olympus 75mm 1.8 wide open, at distance 2m from the object and get DoF of 4cm.

If i want to use 50mm lens instead:

1. How much closer should I move to cover the same frame as previously? (I don't care about the background/ perspective distortion, I just want to cover the same head-and-shoulder)

2. What's my aperture to get that same DoF?

Can you please present the formula as well?

Thanks.

 Albert Ang's gear list:Albert Ang's gear list
Canon EOS 6D Canon EF 35mm f/2.0 Canon EF 50mm f/1.4 USM Canon EF 85mm f/1.8 USM Canon EF 17-40mm f/4.0L USM +4 more
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