Humboldt State University ® Department of Chemistry
Robert A. Paselk Scientific Instrument Museum
Stereoscopic Microscope No. 25
Humboldt State College, 1956
This is a general purpose, low magnification (3 150 x) microscope used for three-dimensional viewing in biology (sometimes referred to as a dissecting scope), assembly and inspection in industry, etc. This type of low power, binocular microscope was first designed by Greenough in 1897, and was first manufactured by Zeiss. It consists of two independent microscopes with erecting prism systems focused on the same object from slightly different angles to give an exaggerated stereoscopic view. Because of the inclinations of the optical axis of the two microscopes from the vertical, only the center of the field is in focus for both, however, the composite image appears sharp over the entire field due to the opposite nature of the focusing errors, the accommodation of the eye, and the great depth of view of the low power objectives.
The microscope is 12.5" tall in the fully closed position. There are two 15x eyepieces in inclined prism housings and 1x, 3x, and 6x paired objectives mounted on the turret (AO Spencer Model 25LG below in Research). The glass stage is 4 1/4 x 51/4". The stand is cast iron, with the entire instrument has black japanned finish with chromed highlights (focusing knobs & rack, turret, etc. The plano concave mirror is 2.5" dia. The serial number, 363733 is engraved with white fill on the top of the left prism housing. The AO shield and Spencer are on the right housing. The instrument had a decal: STATE OF CALIFORNIA HUMBOLDT COLLEGE 13825 on the top of the right leg on the horse shoe base. According to HSU inventory the instrument was acquired in 1956.
This instrument is described and illustrated as: AO Spencer Stereoscopic Microscope No. 25LG, Cat. No. 58-642 on pg. 614 of the 1950 Adolph Frese Corp. Scientific Instruments Catalog, and AO Spencer Stereoscopic Microscopes Nos. 25 and 25L on pg. E-9 & 10 of the AO Spencer Instrument Division Catalog (c. 1953). The same microscope (in the 1x, 2x, 3x option, 25F) also appears as Cat. No. 37381 on pg. 708 of the 1940 BKH Catalog No. 40 (though it appears in the photograph to have black crinkle paint on the stand and body), while Model 25LG (1x, 3x, 6x, inclined eyepieces) but with gray finish and Bakelite focusing knobs appears in the 1963 BKH Catalog No. 63 as Cat. No. 42129 and the 1978 VWR Scientific Catalog as Cat. No. 41915-000 on pg. 768. The Spencer stands in the 1934 Braun catalog are significantly different.
1Needham, George Herbert. The Practical Use of the Microscope. Charles C. Thomas Publisher. Springfield. (1958) p. 64.