Objectives and other optical assemblies include a reflective surface that is truncated at or near a focus based on a curvature of the reflective surface. A specimen is situated at or near the focus of the reflective surface, so that the reflective surface captures and collimates optical radiation emitted from the specimen. The reflective surface can be defined on an optical substrate along with a lens surface, so that an illumination flux is focused on the specimen by the lens surface, and a secondary light flux produced in response to the illumination flux is captured and collimated by the reflective surface.