https://www.karltaylorphotography.com/blog/inverse-square-law-light-part-1/

https://www.linkedin.com/posts/davidgruwierlarsen_you-can-render-super-realistic-custom-bokeh-activity-7148259483440381952-I9hi

To achieve a custom pinhole camera effect with a custom bokeh in Arnold Raytracer, you can follow these steps:

1. Set the render camera with a focal length around 50 (or as needed)
2. Set the F-Stop to a high value (e.g., 22).
3. Set the focus distance as you require
4. Turn on DOF
5. Place a plane a few cm in front of the camera.
6. Texture the plane with a transparent shape at the center of it. (Transmission with no specular roughness)