Figure 11.

Front and side views of the Keplerian (terrestrial-erecting) in-the-lens telescope design using polarizing beam splitters and spherical mirrors. Quarter wave plates (λ/4) are inserted between the beam splitters and the mirrors. Half of the light is lost at the first reflection in the beam splitter but ideally the quarter wave plate assures that the light reflected from the mirror is polarized to pass unaffected through the beam splitter. This light polarization causes no light to be lost through both passes in the second beam splitter. The occluder in front of the ocular beam splitter is required to block the see-through view and increase the contrast of the magnified image. The ocular and objective are shown at different vertical positions on the carrier only to facilitate the side view illustration; they can be placed at the same height if needed.