Several different types of achromat have been devised.

Dollond's son Peter invented the apochromat, an improvement on the achromat, in 1763.

Apochromats are also corrected for spherical aberration at two wavelengths, rather than one as in an achromat.

The breakthrough was to use glasses of maximum refractive index difference but equal dispersion in each achromat.

The first-order design of an achromat involves choosing the overall power of the doublet and the two glasses to use.

The beam reaches the chicane after being turned by 180 in the first triple bend achromat ARC1.

The triple achromat, which reduced secondary colour defects, was invented in 1763 by Dollond's son Peter Dollond.

The converging solar beam from the objective can be diverted to a high dispersion spectroheliograph with Littrow arrangement using a 3.43 m achromat.

It can be further minimized by using an achromatic lens or achromat, in which materials with differing dispersion are assembled together to form a compound lens.

An achromatic lens or achromat is a lens that is designed to limit the effects of chromatic and spherical aberration.

Introduced in 1931, the Imagon is an achromat doublet uncorrected for spherical aberration used together with diffusion discs ("sink strainers").

The most common type of achromat is the achromatic doublet, which is composed of two individual lenses made from glasses with different amounts of dispersion.

The Protar's front achromat used older glass, but the rear achromat used high index glass.

English optician Chester Moor Hall (1703-1771) develops an achromatic lens (or achromat) commonly used as the objective of small refractor telescopes.

Each cell has two bending magnets detuned to allow some dispersion in the straights - the so-called bouble-bend achromat structure - and thus reduce the overall beam size.

The Barlow lens, a negative achromat magnifier invented by Peter Barlow in 1833, is still sold to increase the eyepiece magnification of amateur telescopes.

An apochromat, or apochromatic lens (apo), is a photographic or other lens that has better correction of chromatic and spherical aberration than the much more common achromat lenses.

Chevalier reversed the lens (originally designed as a telescope objective) to produce a much flatter image plane and modified the achromat to bring the blue end of the spectrum to a sharper focus.

The ring is formed by 36 dipole magnets of 1.4 tesla magnetic field, combined in 12 groups of three (triple bend achromat, TBA) for achromatic deflection of the electron beam.

An additional advantage of this lattice is that the two long gaps between the focussing and defocussing quadrupoles in the achromat section provide a lot of space for accommodating beam diagnostics and vacuum devices.

These included an eighteen inch quadrant, a two foot transit instrument, three Hadley sextants, an achromat heliometer, a two foot achromat refractor, a Gregory reflector and many clocks.

He used a two-lens achromat refractor and a weak solar filter (smoked glass) and reported seeing a bump or bulge of light ("Lomonosov's arc") off the solar disc as Venus began to exit the Sun.

Dollond's reputation, especially with his father being a Fellow of the Royal Society as a result of his invention of the achromat, provided the company with the de facto right of refusal on the best optical flint glass.

Reversing the lens did increase chromatic aberration but this could be somewhat corrected by adjusting the achromat to bring colors at the blue end of the spectrum into focus to match the blue sensitive nature of the photographic emulsions being used.

He came up with the Petzval Portrait (modern Austria) in 1840, a four element formula consisting of a front cemented achromat and a rear air-spaced achromat that, at f/3.6, was the first wide aperture, portrait lens.