Introduction

The Universal Stage is one of the oldest and most useful accessories in the armamentarium of the polarized-light microscopist.  It is conventionally used to examine thin sections of rocks, minerals, slags, ceramics, and concrete, or grain mounts of minerals and other single phase or concentrates in solid or liquid mount; even single large crystals and gemstones can be examined.

The particle microscopist normally mounts an unknown in a liquid or thermoplastic medium that allows for the changing of the sample’s orientation by applying pressure to the edge of a round coverglass, so as to maneuver the particle into the most favorable position for measuring crystal angles, observing interference figures, etc.  However, when one is looking at a thin section of rock, the minerals comprising the rock are at various, fixed orientations, and not much can be done about it when using a flat stage.  The universal stage is designed to both rotate 360° and to tilt such a thin section 40°-50° through any of several axes.  One of the first polarizing microscopes was built by Amici in 1844, and this microscope had a built-in E/W tilting axis incorporated outside of its inner, concentric movement.  The biggest problem observed when using this instrument was due to refraction of the light at high angles of tilt, but by 1875 Adams solved that problem by adding small concentric hemispheres above and below the crystal.  By the end of the century (1889-1896) Fedorov had designed the prototype of what would be the modern attachment universal stage.  In the next two decades, Max Berek designed an attachable universal stage for Leitz that incorporated a number of improvements, and is the instrument that is in use today.  Over time, 3-axis, 4-axis, and 5-axis universal stages appeared, although the 4-axis version is the one most commonly used.  In addition to the early universal stage made by Fuess, and others, modern versions have been made by Leitz, Zeiss (Oberkochen), Jena (Zeiss Jena), Bausch & Lomb, Cooke, Nikon, the Russian-made LOMO, and copies of the Leitz made in China.  Although no longer made by the major manufacturers, several Leitz and Chinese-made versions have been available on eBay^® in the last year.

Incentive for Modification of Olympus BX51

The College of Microscopy, Westmont, Illinois 60559, recently had the opportunity to offer a course of instruction in Universal Stage Methods for the Identification of Crystalline Materials (COM170), taught by Daniel E. Kile, formerly with the United States Geological Survey, and author of the beautifully-illustrated monograph, The Petrographic Microscope (see online review in the Book Review section.).  The problem, however, was that the universal stage itself requires considerable space between the microscope stage and the front of the objective; the vast majority of microscopes as currently manufactured do not allow for the required amount of space.  It would be necessary to adapt the College of Microscopy microscopes – Olympus BX51 polarized light microscopes – to accept the Leitz universal stage, which is the model that was to be used in the class.  This was the incentive for preparing the modifications described in this article.  The modifications involved only two tasks; namely, (1) make a riser block to increase the distance between the microscope stage and the objective, and (2) make an adapter plate that would both accept the Leitz universal stage, and attach to existing threaded holes in the Olympus stage.

The Riser Block

There is precedent for the use of a riser block:  the Leitz 4-axis universal stage needs so much room above the stage that even a large research-grade microscope like the Leitz Ortholux-Pol requires that the entire body tube be raised by about 18 mm, and secured with a riser block stop.  Also, a commercially available riser block was made for the Zeiss Universal Microscope.  This Zeiss Universal Microscope Riser Block raises the main arm of the Universal microscope 34 mm higher above the base of the instrument.  [Incidentally, although the riser block described in this article raises the body tube above the stage, the Olympus BH2-Pol would require a riser block to raise the main body above the base, in the same way that the Zeiss does.]

Examining the Olympus BX51-Pol, it was decided that the simplest way to acquire the needed extra room above the stage was to simply raise the entire casting that held the observation tube and Bertrand lens unit.  The configuration of the removed casting immediately suggested the use of a common wood 2”x 4” for the prototype.  Accordingly, measurements were made, and a 5 ½” length of 2”x4” was sawn to be 3” wide, and four ¼” holes were drilled to correspond to the holes already in the casting.  A small elevation in the casting also required that a relief hole be drilled in the wood to accommodate the elevation.

Figure 1 is a photo of the underside of the prototype riser block, showing the relief hole drilled for the elevation in the casting.  In this first version, the four mounting holes are shown lined with metal tubing, but these were dispensed with in the final version.  The finished riser block was painted flat black to match the now-exposed, unfinished lower portion of the casting, and to complement the microscope’s other black accents.

click image to enlarge (84K) Figure 1

click image to enlarge (80K) Figure 2

Figure 2 (Download PDF) is an engineering drawing of a proposed production riser block made from 3” x 1 ½” aluminum bar stock, with black anodized finish.  This drawing provides all of the necessary dimensions.

To make up for the added thickness of the riser block, the four normally supplied mounting screws were replaced with four longer screws, #10 – 32 x 2 ½”.

Figure 3 is a side view of the installed riser block, and Figure 4 is a rear three-quarter view of the installed raising block.

click image to enlarge (69K) Figure 3

click image to enlarge (96K) Figure 4