Extension tubes move the lens away from the sensor so it focuses closer. Added magnification is roughly tube length ÷ focal length, so short lenses gain the most.
Enter your lens's own maximum magnification for the total.
How it works
Δm ≈ extension ÷ focal; exposure factor (1 + m)².
FAQ
Do tubes affect image quality?
They contain no glass, so optical quality is preserved, but lenses not designed for close focus may soften at the edges.
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