| diopter | <microscopy> An optical unit representing the reciprocal of the focal length (in metres) of a lens, in terms of the metre. A 1 diopter lens has a focal length of 1 metre, a 2-diopter lens has a focal length of 1/2 metre, etc. The diopter expresses the power as in spectacles or other weak lenses. (05 Aug 1998) |
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| prism diopter | The unit of measurement of the deviation of light in passing through a prism, being a deflection of 1 cm at a distance of 1 m. (05 Mar 2000) |
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