Depth of field question

Started Dec 22, 2012 | Discussions thread
Leonard Shepherd
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Re: To help clarify
In reply to Leon Obers, Dec 26, 2012

Leon Obers wrote:


It is already by optical formulas that by enlargement the effective aperture shall be more small.When focal length is not changing, enlargement of 1:1 the effective aperture shall be 2 stops more small than at infinity. So a f2.8 lens shall be effective f5.6 of the focal length at this enlargement by today's Micro Nikkors, the effective aperture opening shall be less small than f5,6shorteningBy the

To help clarify a theoretical 105mm lens of symmetrical design at 1:1 focus has the angle of view of a 210mm lens at infinity focus; and transmits two stops less lights than when focused at infinity.

The Nikon 105mm f2.8 macro D is not symmetrical at 1:1, and changes to an equivalent 78.5mm f2.1. It transmits only one stop less light compared to 2 stops less with a theoretical symmetrical lens.

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Leonard Shepherd
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