Mirror Equation Calculator
1/f = 1/d_o + 1/d_i. Same form as lens but with mirror sign conventions.
Result
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How to use this calculator
- Pick what to solve.
- Enter known values.
- Mind sign conventions for concave/convex.
About this calculator
Mirror equation: 1/f = 1/d_o + 1/d_i. Sign convention: concave (converging) f positive; convex (diverging) f negative. Real images form on the reflective side (d_i positive); virtual images appear behind the mirror (d_i negative). Concave mirrors: bathroom shaving, dental, telescope primaries. Convex mirrors: passenger side car (objects appear smaller but wider field of view).
Frequently asked
Concave vs. convex?+
Concave: curves inward (like a spoon's bowl side). Convex: curves outward.
Why "objects in mirror are closer"?+
Convex mirror produces virtual diminished image. Brain reads diminished as far away — but it's actually closer than perceived.
Magnification > 1?+
Yes for concave when d_o < |f|. The classic shaving mirror — close = larger upright.
Plane mirror?+
f → ∞. d_i = -d_o (virtual, behind by same distance). M = 1 (same size, upright, reversed).
Telescopes?+
Newtonian: concave primary mirror at one end, secondary deflects to eyepiece. Big aperture = lots of light.
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