Editing Hyperfocal distance (section)

====Definition 1====
An object at distance {{mvar|H}} forms a sharp image at distance {{mvar|x}} (blue line). Here, objects at infinity have images with a circle of confusion indicated by the brown ellipse where the upper red ray through the focal point intersects the blue line.

First using similar triangles hatched in green,
<math display="block">\begin{array}{crcl}
           & \dfrac{x-f}{c/2} & = & \dfrac{f}{D/2}  \\
\therefore & x-f              & = & \dfrac{cf}{D}   \\
\therefore & x                & = & f+\dfrac{cf}{D}
\end{array}</math>

Then using similar triangles dotted in purple,
<math display="block">\begin{array}{crclcl}
           & \dfrac{H}{D/2} & = & \dfrac{x}{c/2}                                              \\
\therefore & H              & = & \dfrac{Dx}{c}   & = & \dfrac{D}{c}\Big(f+\dfrac{cf}{D}\Big) \\
           &                & = & \dfrac{Df}{c}+f & = & \dfrac{f^2}{Nc}+f
\end{array}</math>

as found above.