What is 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.

How is magnification calculated?

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.

What is the difference between optical and digital magnification?

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.

Why do macro lenses have long focal lengths?

Longer focal lengths provide more working distance at the same magnification. A 100mm macro at 1:1 focuses at ~300mm from the subject, while a 60mm macro at 1:1 focuses at ~180mm. More working distance avoids scaring insects and reduces the chance of casting shadows on the subject.

PhotoCalcs

Magnification Calculator — Optical Magnification

Calculate the optical magnification ratio from focal length and subject distance.

Focal Length

Lens focal length

Subject Distance

Distance to subject in mm

Sensor Width

e.g. 36mm for full frame

How We Calculate This

This calculator uses the thin lens magnification formula:

Magnification

M = f / (d - f)

Where f = focal length and d = subject distance (both in mm).

Subject Coverage

Subject width filling sensor = sensor width / M

At 1:1 magnification on full frame (36mm sensor width), a subject 36mm wide fills the frame.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates based on standard optical and photographic formulas. Results may vary with specific equipment.