A simple multipurpose double-beam optical image analyzer
  In the paper we present a low cost optical device which splits the light in the focal plane into two separate optical paths and collimates it back into a single image plane, and where a selective information processing ca be carried out. The optical system is straightforward and easy implementable as it consists of only three lens and two mirrors. The system is dedicated for imaging in low-light-level conditions in which widely used optical devices, based on beam-splitters or dichroic mirrors, suffer from light loss. We expose examples of applications of our device, using a prototype model. The proposed optical system may be employed for: monitoring the objects located in different distances from observer (1), creating regions of different magnification within a single image plane (2), high dynamic range photometry (3), or imaging in two wavelength bands simultaneously (4). 
Adam Popowicz, Tomasz Blachowicz
astro-ph.IM