Magnification Calculator — Optical Magnification

Magnification is the ratio of the image size on the sensor to the actual subject size. At 1:1 (1x) magnification, a 10mm subject produces a 10mm image on the sensor. At 1:2 (0.5x), a 10mm subject creates a 5mm image. Macro lenses typically achieve 1:1 magnification.

Magnification M = focal length / (subject distance - focal length). As the subject gets closer to the focal length, magnification increases. At twice the focal length distance, M = 1:1. At infinity, M approaches zero.

Optical magnification is the actual image size on the sensor relative to the subject. Digital magnification (digital zoom) simply crops and enlarges a portion of the image, losing resolution. Optical magnification preserves full resolution; digital magnification reduces it.

Longer focal lengths give more working distance at the same magnification. At 1:1, the lens-to-subject distance equals twice the focal length: a 100mm macro sits ~200mm from the subject (real-world working distance ~150mm from the front of the lens), while a 60mm macro sits ~120mm away (working distance ~90mm). More working distance avoids scaring insects and reduces the chance of casting shadows on the subject.