127. Ross Concentric Lens, c. 1893
Signed: 'N1 50725 ROSS LONDON Patent 3 inch Concentric'.
Two achromatic doublets of the new barium crown glass of high refractive index and a new flint glass of low index, but because of spherical it could only be used at small aperture (f16). Focal length of 75 mm and between lens rotating disc set of stops. Was superseded by the Zeiss Protar lens.
Length 30 mm, diameter 35 mm.
Inventory no. 79,148.