At close focus the lens's effective aperture gets smaller than the number on the barrel: at 1:1, f/8 behaves like f/16. Depth of field also shrinks to millimeters.
Enter magnification, aperture and sensor to see the effective f-number, light loss and total depth of field.
How it works
N_eff = N × (1 + m/P). Total DoF ≈ 2·N·c·(1 + m/P) ÷ m².
FAQ
Do cameras show the effective aperture?
Many modern bodies with native macro lenses display it automatically; with tubes or adapters you may need this calculator.
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