Difference between revisions of Optics related math

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 ===From blur horizon of naked eye===
-From your cm measurement...
+Note that this does not take either [[cylinder]] ([[astigmatism]]) or [[vertex distance]] into account.
+Your [[cm measurement]] gives you the distance the eye can see when it is fully relaxed. You want
+a (diverging) corrective lens which puts a virtual image of the source object there. So we can solve
+the thin lens equation to find <math>f</math> for an arbitrary source object distance <math>s</math>
+given <math>s' = -cm</math>.
+For full correction, that's easy : <math>s=\infty</math> and so <math>f=s'</math>. Eg if your
+blur horizon is 20cm you need a 5D correction.
+For differentials to use a screen at, say, 50cm, just use <math>\frac{1}{f} = \frac{1/0.50} + -\frac{1/0.20} = -3D</math.
+(Which is consistent with the previous version, subtracting 2D from the full correction of 5D.)
 ==Point of refraction==