That the subject is projected onto the sensor at life size: ten millimetres of insect covers ten millimetres of sensor. It is a ratio of sizes, not a measure of sharpness or of working distance.
The ratio compares two sizes: the subject, and its image on the sensor.
Reading it
1:1 means life size — a subject one centimetre across is projected one centimetre across. 1:2 is half life size, 2:1 twice. The notation is a proportion and it holds regardless of sensor format, though the framing that results does not: a smaller sensor takes a narrower rectangle out of the same projection.
What the ratio omits
Sharpness at that magnification, which is not published in a comparable form. Working distance, which is a separate figure — the minimum focus distance — and the one that decides whether you can light the subject at all. And depth of field, which at life size is a matter of millimetres and follows from the aperture, not from the ratio.
Macro lenses and close-up lenses, kept apart
Macro lenses are a family here with a measured ratio in a minority of titles. The neighbouring family is close-up lenses — screw-in elements that let an ordinary lens focus nearer, published by diameter rather than by ratio, and sitting in the filter group for exactly that reason.
Why the confusion is common
Because listings use the word macro for anything that focuses close, and the ratio is the figure that distinguishes a true 1:1 lens from a lens that merely focuses nearer than most. Where a listing gives no ratio, it has not made the claim.
Where this page and the maker’s own manual disagree, the manual decides. Every focal length, aperture, guide number, stop of stabilisation, load rating and sealing claim on this page is reported from the manufacturer’s own documentation, with its unit written as published, and named as such — none of it is measured here. An engraved figure is reported as the maker engraves it, and is never restated in another convention, because the two are not the same number. And the statement repeated rather than assumed: an equivalent focal length is arithmetic, not a measurement. The millimetres engraved on a barrel describe the optic itself and never change; what changes is how much of the projected circle a given sensor takes out of it. An equivalence is that ratio applied to the engraved figure, and it appears here as a calculation with its format named, never in place of the number on the lens.
What people ask before they commit
Is a 1:2 lens half as good?
It reaches half life size, which is a different capability rather than a lesser quality. Many lenses sold as macro reach 1:2 or 1:3, and for flowers or objects that is often enough — the ratio tells you what fits the frame and nothing about how well it is rendered.
Why does working distance matter more than the ratio?
Because at life size the lens is close enough to shade its own subject and to frighten anything alive. Two lenses at the same 1:1 ratio can differ greatly in how far away they achieve it — the longer focal length working further back — and that distance is published as a minimum focus figure.
Last reviewed 12 September 2026