VAN HEURCK MICROSCOPE (parachromatic objectives):

c. 1910

Maker: W. WATSON & SONS LTD.

Four classes of objectives were available at time of the manufacture of my Grand Van Heurck microscope about 1910. These included ordinary Achromatic, Parachromatic, Holoscopic, and Apochromatic types, in increasing order of resolution and cost.

For a long time, the Holos or Holoscopic objectives were Watson's premier objective. Nearly apochromatic, with precise correction of spherical aberration, Watson touted them as equal, or nearly equal to true Apochromats. Just one class below these were the celebrated 'Parachromatic' or 'Para' objectives.The Para objectives with this microscope at this time include the 3 inch (75 mm), 2 inch(50 mm), 1¹/₂ inch(shown only in top image), 1 inch (25 mm),²/₃ inch(17 mm), ¹/₆ inch(4 mm), and the ¹/₈ inch(3 mm). You will note that the 1 inch and also the earlier ²/₃ inch objectives are not labelled as 'Parachromatic' but are, nonetheless, that variety of objective, as is proven by both their n.a. reported for the Parachromatics in the Watson Catalog, and the fact that there are two sets of elements in each of these objectives (Watson's plain achromats had only one set of elements). Note that the Swift 4 inch objective with the set, which closely resembles the Watson 4 inch, is not pictured on this page.