The choice of glass gives the mean refractive index, often written as (for the refractive index at the Fraunhofer "d" spectral line wavelength), and the Abbe number (for the reciprocal of the glass dispersion).
His major achievement at the time was the improvement of the achromatic microscope objective.
Lens | Lens, Pas-de-Calais | Independent Lens | Nicholas Lens | lens | Fresnel lens | Single-lens reflex camera | Panasonic Lumix 45mm lens | Panasonic Lumix G 14mm lens | Panasonic Lumix 20mm lens | Panasonic Leica DG 25mm lens | M42 lens mount | Lens (optics) | Judith of Lens | Digital single-lens reflex camera | Ultra wide angle lens | Through-the-lens metering | Mirrorless interchangeable-lens camera | Lens (Pas-de-Calais) | lens (anatomy) | Lambert II, Count of Lens | Bernard Lens | Achromatic lens | Zoom lens | zoom lens | Telephoto lens | single-lens reflex camera | Sidney Lens | Panasonic Lumix G X Vario PZ 45-175mm lens | M.Zuiko Digital ED 9-18mm f/4-5.6 lens |
Amongst the latter were a Dollond 46-inch achromatic, aperture 3¾ inches, and the one Cassegrain reflector constructed by Short, of 24 inches focus and 6 aperture, known among opticians as 'Short's Dumpy.'
Optical systems in rigid borescopes can be of 3 basic types: Harold Hopkins rod lenses, achromatic doublets and gradient index rod lenses.