There are two categories of lenses, both distinguished by a different numerical aperture: SLW (wide)and SLH (high). Each NA type is appropriate for different applications and exhibits different alignment sensitivities (see Technical Charts Table 2).

While the numerical aperture is a maximum at the center of the lens aperture, the actual NA is a function of the ray parameters (height and angle) for each ray that strikes the lens’ surface. Click to the Appendix of this guide for an illustration of how the NA depends on these parameters.