An alternative to achromatic doublets is the use of diffractive optical elements. This was especially true in refracting telescopes, before the invention of achromatic objective lenses. Examples of some of the largest achromatic refracting telescopes, over diameter. This gray color template includes both achromatic and chromatic grays. In practice, the lens will be an achromatic doublet. Most are classical Great refractors, which used achromatic doublets on an equatorial mount. It also featured an achromatic lens with a 10-fold magnification. IDC clarity grading is by examination using a 10x achromatic, aplanatic loupe in normal light. Ramsden is also responsible for the achromatic eyepiece named after him. The Oschin Schmidt was given an achromatic corrector and provisions for autoguiding. For an achromatic dispersive lens the converse must be adopted. John Dollond was the first person to patent the achromatic doublet. By 1812, Fraunhofer had succeeded in creating an achromatic objective lens in diameter. The 'K' component absorbs all wavelengths and is therefore achromatic. Despite this mechanical simplicity, high-quality achromatic lenses were standard.