Adapting a prototype zoom lens to work outside its zoom range

摘要

Prototype zoom lenses should be designed with flexibility. One never knows what the future use of a prototype as-build lens will be. In a prior design of a large-image-format zoom lens used for proton radiography, extra back focal distance was constrained in the design to allow for future insertion of extra lenses. These added lenses can change the magnification to a different camera system, having a smaller image size. Three single commercial lens elements were mounted into a commercial variable-length housing barrel that was attached to the back of the zoom lens using a 3D-printed flange. This new design has been adapted to support neutron radiography; the new configuration collects light from a thick, blue-light-emitting scintillator. After the initial request was made, it took us only three weeks to design, assemble, and conduct imaging tests. The scintillator's light travels 24 inches before entering into the zoom lens. A large pellicle is inserted into the optical path to keep the zoom lens and camera out of the neutron flux. Because of reduced resolution from the volume scintillator, a five-axis self-leveling alignment laser was sufficient to adjust the tilting of the scintillator, pellicle, zoom lens, and camera. The design process for picking suitable COTS lens elements will be discussed.