In a previous role I had a coworker who would always joke that I was the “Special Projects Engineer”. This was one of those special projects.
An engineer had just left, and in addition to my controls and acoustics duties, due to previous navigation and computer vision projects, had taken over the role of creating a non-imaging optic that needed to have a very precise projection geometry. We were working with an optics contractor, and he was very good, but many of the designs that he proposed were outside of our budgetary constraints. Ultimately, we proceeded using an approach that I came up with by inverting a cold shield design for telescope optics.
Now, I’m not going to say exactly what this was used for, but I believe the design process is worth documenting for other’s use. In the above image, the square near the top-middle of the CAD drawing is a light source, whose projection geometry is dictated by the narrowest lines at the outlet of the baffle. This type of vaned baffled is designed to not allow anything under a fourth order reflection to escape the aperture. The design process is basically an inversion of that proposed in section 9.2.1 of Stray Light Analysis and Control, E. Fest, where the author constructs an algorithm to create a cold shield to restrict the field of view of an imager to prevent blinding from stray ambient light.
This approach allowed the baffle to be molded, and an SPI A-1 surface finish was dictated to try to ensure all reflections within the baffle were specular, and not diffuse.