Benz, my distant relative but reliable source in Jena (hometown of Carl Zeiss), was birdspotting this morning and noticed this prototype in the hands of a fellow, er, byrder (?). It certainly would fill a gap in the available range of lenses. From what dear old uncle Benz gathered, the lens is a true 500 mm (i.e. 1 voll meter equivalent) with a very relative yet fixed "aperture" of f/8. A minute limitation since one can stop it down thanks to a screw-in accessory cross-polarizing filter, without the diffraction pleaguing a mechanical iris.