Originally Posted by
Dan Fromm
Key magic formulas:
extension = focal length *(magnification + 1)
Extension is measured from the film plane to the lens' rear node. For most LF lenses the rear node is close to the diaphragm.
Front node to subject distance = focal length *(magnification + 1)/magnification
For most LF lenses the front node is close to the diaphragm.
effective f/ number= f/ number set * (magnification + 1)
You're going to need 600 mm extension to shoot a 300 mm lens at 1:1. Front node to subject distance will also be 600 mm. There are some subjects for which that much working distance is helpful, but in general you'd be better off using a shorter lens at 1:1.
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