Can an Aspheric Lens Narrow the FOV for Motion Detection Systems?

[Tone L]

TL;DR Summary

Curious if fresnel lenses are needed for motion detection.

I want to build a motion detection system, however I want to narrow field of view. I cannot find a Fresnel lens with a narrower FOV than 30 degrees. Was looking for something around 20 degrees.

Can I use an aspheric lens to achieve this, does anyone know?

 

[berkeman]

You just want to narrow your FOV with a pre-lens? What dimensions? Can you not just use some blocking pieces to narrow the FOV? More details and a sketch would be helpful. Thanks.