Sagitta (optics)

In optics and especially telescope making, sagitta is a measure of the glass removed to yield an optical curve. It is approximated by the formula

S = \frac{r^2}{2 \times \text{ROC}}

or

S = \frac{r^2}{4 \times \text{focal length}}

A good explanation both of this approximate formula and the exact formula can be found at http://www.opticampus.com/popcourse.php?url=high_powered/#appendix

See also

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