• Pixel-art sticker of Dioptron, personifying Optical Power of a Lens, with the caption “Shorter Focus, Stronger Lens.”

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Dioptron

Optical Power of a Lens Physics

\[P = \frac{1}{f}\]
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$4.99 USD
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Meet Dioptron, a pair of glasses who rates lenses by how strongly they bend light. Optical power is one over the focal length in metres, measured in dioptres: a 0.5 m lens is 2 D, a 0.25 m lens 4 D. Diverging lenses for short sight have negative power. Pixel-art kiss-cut sticker in 2, 3, 4 and 6 inches; equation, symbols and sources in the physics panel below.

Size
Surface

Flat $6 shipping worldwideMade to order, ships in 2–5 business days

Details

Size3″ × 3″

3″ × 3″ kiss-cut sticker.

Shipping

Flat $6 shipping on every order, worldwide, whatever's in it.

Delivery times & where we ship

Returns & replacements21 days

Every item is printed to order, so we can’t accept returns or exchanges for change of mind, or if you ordered the wrong size or colour.

Print defect, misprint, damage or the wrong item? We’ll send a free replacement, or a refund if you prefer. Report it within 21 days of delivery with a photo; no need to send it back.

Full refund & replacement policy

The physics

Meet Dioptron, a pair of glasses who measures lenses by how strongly they bend light.

A lens brings parallel rays of light together at its focal point, a distance f away. A lens that bends light sharply has a short focal length, and a weak lens has a long one. Optical power expresses this strength as P = 1/f.

When f is in metres, the power is in dioptres, written D. A lens with a focal length of 0.5 m has a power of 1 / 0.5 = 2 D. A lens with a focal length of 0.25 m has a power of 4 D, so halving the focal length doubles the power.

Converging lenses have positive power and diverging lenses have negative power. A prescription of −2 D describes a diverging lens, which is the kind used to correct short sight.

Dioptres are handy because the powers of thin lenses placed close together simply add, which is why opticians use them on every prescription.

Equations

\[P = \frac{1}{f}\]
SymbolMeaningUnit
\(P\) optical power \(\mathrm{D}\)
\(f\) focal length \(\mathrm{m}\)

Sources

  1. OpenStax College Physics 2e — Physics of the Eye
  2. Wikipedia — Optical power

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