Lens: Add option to draw focal point only on one side about tikz-optics HOT 2 CLOSED

I have to think about it, it would be easy but I am not sure that even the draw focal points style is a good idea (it is not so easy to customize, and is mainly there as a shortcut).
But you can use

\begin{tikzpicture}[use optics]
\node[lens] (L) at (0,0) {};

\node[optics/mark a cross] at (L.west focal point) {};
\end{tikzpicture}

to get

Indeed, the same works with east focal point, and any shape instead of optics/mark a cross.

from tikz-optics.

Ok, that's not more code than using the "draw focal points", so this solution is surely good enough.

from tikz-optics.