N.A. Calculator Home > Technical Acceptance Angle Calculator © 2003 FTI All Rights reserved Core Glass N1 Clad Glass N2 Numerical Aperature Critical Angle (Degrees) You can use this calculator to identify the numerical aperature and the acceptance angle of any glass combination. N1 is always larger than N2. Therefore, if your result is "NaN", you have reversed the values. Please input again. If you already know the Numerical Aperature of the glass combination, and you'd like to identify the acceptance angle, click here.