Bellows Extension Required

[Pete Suttner]

If I were focusing on a flower 2" in diameter with a 180mm macro lens at 2:1 how much bellows extension would I need? How do you arrive at the answer?

[Dan Fromm]

There are books on this and the topic is discussed on many web sites. Buy a copy of Lester Lefkowitz' book The Manual of Closeup Photography to learn how to think about close up (up to 1:1) and photomacrography (above 1:1).

Short answer, the distance from film plane to lens' rear node given magnification and focal length is focal length * (1 + magnification). 2:1, 180 mm => 180 * 3 = 540 mm.

For lenses of normal construction (that's your 180 macro lens) the rear node is close to the diaphragm.

[Pete Suttner]

Thanks!