s-mount camera

s-mountlensholder

Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

No, there's really not such a thing as a negative numerical aperture. Understand that NA is about an image forming lens, bringing the incoming light (in the case you mentioned, collimated) to a single focus point. Meaning, a net-convex system.

I understand that it's tempting to look at an equation such as NA = n sin θ, and wonder what meaning can be inferred if n or θ were negative.