Macro Magnification Calculator

How extension tubes work

An extension tube moves the lens away from the sensor, letting it focus closer. The added magnification is approximately extension ÷ focal length: 25mm of tubes on a 50mm lens adds 0.5×. Added to the lens's native close-focus magnification, that determines your total reproduction ratio — 1:1 means the subject is projected onto the sensor at life size.

Frequently asked questions

Do extension tubes reduce image quality?

Tubes contain no glass, so they add no optical degradation. You do lose some light (about 2 × log₂(1 + magnification) stops) and lose infinity focus while they're mounted.

Tubes work better on which lenses?

Short and normal focal lengths. The same 25mm of extension adds 0.5× to a 50mm lens but only 0.125× to a 200mm lens — the math in this calculator makes that obvious.

What magnification do I need for insects?

Larger insects (butterflies, dragonflies) work at 0.25–0.5×. Small bugs and fine detail want 1:1 or beyond, where dedicated macro lenses shine.