Photographic lens design screen. It also permits the lens to be mounted in a relatively coarsely threaded focusing mount so that the projectionist can quickly correct any focusing errors. The lenses of the very earliest cameras were simple meniscus or simple bi convex lenses. It was not until 1840 that Chevalier in France introduced the achromatic lens formed by cementing a crown glass bi-convex lens to a flint glass plano-concave lens. By 1841 Voigtländer using the design of Joseph Petzval manufactured the first commercially successful two element lens. Carl Zeiss was an entrepreneur who needed a competent designer to take his firm beyond
Lens (optics) object off the optical axis of the lens is imaged, where rays pass through the lens at an angle to the axis θ. Rays that pass through the centre of a lens of focal length "f" are focused at a point with distance from the axis. Rays passing through the outer margins of the lens are focused at different points, either further from the axis (positive coma) or closer to the axis (negative coma). In general, a bundle of parallel rays passing through the lens at a fixed distance from the centre of the lens are focused to a ring-shaped