Achromatic 44mm and 47mm Focal Length

These are 44mm or 47mm focal length 20mm diameter achromatic lenses (Revere or equivalent) which correct for spherical and chromatic aberrations. They come in metal mounts which can be used in home made stereo slide viewers for interocular adjustments. The mounts can be easily removed to allow the lenses to be used as replacements for any viewer which uses 20mm diameter lenses.