numeric aperture

nu·mer·ic ap·er·ture (N.A.),

defined by the formula n sine a, where n is the refractive index of the medium between the object and objective lens and a is the angle between the central and the marginal rays entering the objective.
Farlex Partner Medical Dictionary © Farlex 2012
References in periodicals archive ?
"To fully optimize the system, there is an dectrically-conductive thermal control coating on the outer surface of the FCS2 microaqueduct slide, thus adding thermal uniformity even during experiments with periods of no perfusion flow." With the addition of the Bioptechs Objective Heater system for high numeric aperture applications, the FCS2 has become the prime micro-environmental system for long-term time-lapse studies, such as those Latimer's lab performs.