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# What is dioptre

Particularly when purchasing bench magnifiers, the term Dioptre is often used in place of magnification, as an indicator of the resulting enlargement of the sample being veiwed.

Dioptre (D): Describes the refractive (light bending) capability of a lens, it is proportional to the curvature of the lens. The focal length (working distance) and dioptre values of a lens are directly related. The dioptre of a lens, can be established by viewing from a distance of 25 cm above the lens, then move the object to the greatest distance below the lens where it remains in sharp focus. Divide this distance into 100 cm. The result is the dioptre of the lens - e.g., if the object is at a 33 cm distance, then it is a 3-dioptre lens (100/33 = 3D). Each dioptre increases the size of the viewed object by 1/4 (25%) when the object is at its full focal length from the lens. This is the opposite of what usually happens with compound optical systems (microscopes etc), where the magnification increases when the focal length is decreased.

We have tabulated a guide for magnification levels, as compared to Dioptre:
2 Dioptre = 1.50x Mag
3 Dioptre = 1.75x Mag
4 Dioptre = 2.00x Mag
5 Dioptre = 2.25x Mag
7 Dioptre = 2.75x Mag
8 Dioptre = 3.00x Mag
9 Dioptre = 3.25x Mag
11 Dioptre = 3.75x Mag
13 Dioptre = 4.25x Mag
16 Dioptre = 5.00x Mag
18 Dioptre = 5.50x Mag
20 Dioptre = 6.00x Mag