To determine and eliminate or reduce stray light influence during the design phase.
State of stray light for initial construction of lens system
The main source of stray light (also known as parasitic light) in this catadioptric lens system is scattering that occurs at the edge of lenses and elements of lens mounting. The yellow lines show stray light reaching the image plane directly or indirectly.
Adding internal hood to reduce direct stray light
First, we added an internal hood (shown in purple) for a primary mirror in order to reduce the amount of direct stray light entering the image plane.
Adding external hood to remove the rest of direct stray light
Attaching an external hood (purple) to the secondary mirror eliminates the rest of stray light going directly to the image plane.
Modifying optical properties to reduce indirect stray light
By tuning optical properties of the elements (e.g. lens holder shown in purple) composing the lens system, we tried to reduce stray light reaching the screen indirectly. Tuning includes modification of surface roughness, directional characteristics of reflectivity and construction of the hoods.
Visualization of image formed on screen
The amount of stray light that reaches indirectly the screen can be visualized as a gray-scale image. The light gray area shows a relatively higher level of indirect stray light incidence in comparison with other areas.
State of stray light for initial construction of lens system
Adding internal hood to reduce direct stray light
Adding external hood to remove the rest of direct stray light
Modifying optical properties to reduce indirect stray light
Visualization of image formed on screen