Looking for a Fisheye Lens shader.

I found on Orbolt, “Domemaster” but it doesn't seem to work correctly as there are no parameters to change FOV as listed in the instructions. And it is not producing the correct distortion.

Will SFX make a Fisheye Lens? 180x360

you could try applying an ‘asad lens’ shader to a camera and playing with the ‘zoom’ and ‘lens curvature’ parameters. this makes a nice fisheye look.

Mantra has a curvature lens built in. You only need to expose the parameter on your Camera.

Select the Camera -> Click the gear icon and -> Edit Parameter Interface
Go to tab Render Properties
Search for Curvature and under View -> Lens Curvature (vm_curvature)
Select it and click the arrow icon to add the parameter. Click Accept.

Under the View tab of the Camera you should now have a Parameter for Lens Curvature. Put it to 0.1 or something and render to see the result.

edit: just realize i am not sure if the vm_curvature can get the result you are looking for.

The equations for equiangular/equidistant and other fish eye projects are easily found. Make a copy of the asad lens, and modify the code to perform the new projection. A lens shader is very simple, and merely maps screen coordinates to ray direction/origin. For an ideal pinhole lens, the ray origin is simply 0,0,0.

https://www.uwgb.edu/dutchs/structge/sphproj.htm [www.uwgb.edu]
http://michel.thoby.free.fr/Fisheye_history_short/Projections/Various_lens_projection.html [michel.thoby.free.fr]