How to convert Numerical Aperture to F-Number?

Given a telecentric lens with image side numerical aperture $N\kern-.3emA$ . Then

$ImageSideFNumber = \frac{1}{2 * \tan (\arcsin ( {N\kern-.2emA_{image}}) ) }$

$NA = \sin \alpha$
$\alpha = \arcsin (NA)$
$\tan(\alpha) = \tan (\arcsin (NA) )$
Also
$R = \tan(\alpha) * WD = \tan (\arcsin (NA) ) * WD$
$2*R = 2 * \tan (\arcsin (NA) ) * WD$
$Object Side FNumber = \frac{focal length}{2*R}$
$ImageSideFNumber = Object Side FNumber * Magnification$
$= \frac{focal length}{2*R} * Magnification$
$= \frac{focal length}{2 * \tan (\arcsin ( NA) ) * WD} * Magnification$
$= \frac{Magnification}{2 * \tan (\arcsin ( NA) ) }$