Exit pupil

Tue, 22 Sep 2026 01:00:00 +0000

Exit pupil is the diameter of the beam of light exiting the eyepiece.

The exit pupil can be calculated in several ways:

$$ \small \begin{align} d &= \text{exit pupil (mm)} \newline D &= \text{Aparture (mm)} \newline P &= \text{Power (magnification)} \newline \end{align} $$

$$ \large d=\frac DP $$

$$ \small \begin{align} d&= \text{exit pupil (mm)} \newline D&= \text{Aparture (mm)} \newline f&= \text{eyepiece focal length (mm)} \newline F&= \text{OTA focal length (mm)} \newline \end{align} $$ $$ \large d=\frac {D\cdot f}{F} $$

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Exit pupil