CIRCUIT STAGE VAN HEURCK MICROSCOPE (objectives):
c. 1910
Maker: W. WATSON & SONS LTD.
Serial number: 11970
Objectives with this microscope at this time include one
achromatic type, five parachromatics, five holoscopics, and two apochromatics all by Watson, and a Lietz 1/12 oil immersion lens. As noted below, the Watson Apochromats were made slightly later than the likely production date of this microscope. In addition, as of 1906, Holoscopic objectives were limited to focal
lengths of 1 inch and shorter, so at the time this instrument was sold, available lower power (longer focal length) objectives were either ordinary achromats or parachromatics. Lower power Holos objectives became available later that decade, but the shortest focal length apochromatic remained the 2/3 inch, even through 1928. Eventually the plain achromats, also known as the 'Argus' series were no longer offered, the Parachromatic series being the lowest class Watson made. Also notable, is that although the 2 inch objective in this collection is a Holos, it is not signed as such nor is its can labelled that way. Nevertheless, it must be a Holos as its n.a. is very high, and of the stated size for a 2 inch Holos objective in the Watson catalogs.
Similarly, the 1 inch Parachromatic objective is not labelled on the objective or the can as such but must be as it has two sets of optical elements, and has a n.a. of 0.21.
Objectives with the instrument, all by Watson except as noted,
include an achromatic objectives for low power 3 inch,
the 1/12 inch oil immersion by Leitz, Parachromatics (3 inch, 2 inch, 1 inch, 2/3 inch, 1/6 inch, & two 1/8
inch), Holos (12, 8, 4, and 2 mm oil immersion),
and Watson Apochromatics (4 mm & 2 mm oil immersion):
