John DollondDied 30 Nov 1761 at age 55 (born 10 Jun 1706).English optical instrument maker of optical and astronomical instruments who developed (1758) and patented an achromatic (non- colour- distorting) refracting telescope and a practical heliometer, a telescope used to measure the Sun's diameter and the angles between celestial bodies. In the 1730's, Chester More Hall, an attorney with an interest in telescopes, first discovered that flint glass appeared to have a greater color dispersion than crown glass did at the same magnifications. Hall reasoned that if he cemented the concave face of a flint glass lens to the convex face of a crown glass lens, he could remove the dispersion properties (and thus, chromatic aberration) from both lenses simultaneously. Dollond learned of the technique in the 1750's and developed it. |
