The structure of a polarizing microscope

There are many models of polarizing microscopes, but the main structures of each model are roughly the same, such as the XPB-7 polarizing microscope produced by Jiangnan Optical Instrument Factory in my country (Figure 3-2), the Leitz CM model in Germany Polarizing microscope (Figure 3-3), Japan Olympus BHSP polarizing microscope (Figure 3-4). Taking the XPB-7 polarizing microscope as the main body, this article briefly introduces the main structure of the polarizing microscope and appropriately supplements the differences of the Olympus BHSP polarizing microscope.

The mirror base supports all the mass of the entire microscope. Its shape is a horseshoe shape with three-dimensional columns (Figure 3-2). The Olympus BHSP type mirror base (chassis) is rectangular (Figure 3-4 ). There is a halogen light source behind it, a field diaphragm adjustment ring and a light sheet bracket are installed on the central round hole, a voltmeter is installed in the front, a power switch is installed on the front side, and a voltage that can change the intensity of the light is installed on the right side. Adjustment knob.

Figure 3-2 XPB-7 polarizing microscope produced by Jiangnan Optical Instrument Factory

(According to Li Dehui, 2002)

1—Eyepiece; 2—Mirror Tube; 3—Bernfield mirror; 4—upper polarizer; 5—objective lens clip; 6—test plate hole; 7—objective lens; 8—sheet clip; 9—stage; 10—condenser; 11—lock aperture; 12 - Lower polarizer; 13 - Reflector; 14 - Lens holder; 15 - Stage fixing screw; 16 - Lens arm; 17 - Fine focusing screw; 18 - Coarse focusing screw

The mirror arm is a curved arm (Figure 3-2), its lower end is connected to the mirror holder, and its upper end is connected to the lens barrel. The connection with the lens barrel is equipped with coarse and fine motion focusing screws, which can raise and lower the lens barrel to adjust the focus. Because the lens barrel is straight, the lens arm can be tilted back for ease of observation, but the stage is also tilted accordingly. Do not tilt it excessively during use to prevent the microscope from tipping over. The lens barrel of the BHSP polarizing microscope is tilted and its lens arm is fixed (Figure 3-4). The stage is always level, making it easier to use. There are coarse-motion and fine-motion focusing screws installed at the lower end of the mirror arm, which can raise and lower the stage to adjust the focus. There are scales on the micro-moving spiral, and one scale is equal to 2 μm.

Figure 3-3 Leitz CM polarizing microscope

1—Mirror base; 2—Mirror axis; 3—Winch; 4—Reflector; 5—Mirror arm; 6 — Lower polarizer; 7 — Stage; 8 — Stage fixing screw; 9 — Vernier scale; 10 — Pressing sheet clamp; 11 — Objective lens clamp; 12 — Fine motion screw; 13 — Coarse motion screw; 14 — Objective lens ; 15 - upper polarizer; 16 - Bertrand mirror; 17 - Bertrand mirror spiral; 18 - eyepiece

The reflector is a small round mirror with flat and concave sides, which can be rotated arbitrarily for alignment A light source that reflects light into the microscope's optical system. When using it, try to achieve the required brightness. The BHSP polarizing microscope has no reflector, uses a halogen light source, and adjusts the light intensity through the voltage adjustment knob (Figure 3-4).

The lower polarizer (polarizer) is made of polarizer and is located above the reflector or halogen light source. The natural light waves reflected by the reflector or coming from the light source pass through the lower polarizer and become polarized light with a fixed vibration surface. Use the rotating ring to rotate the lower polarizer to adjust the direction of the vibration surface of the lower polarizer. Usually the vibration surface of the lower polarizer is adjusted in the east-west direction. Generally, the symbol "PP" represents the direction of the vibration plane of the lower polarizer. The lower polarizer is equipped with fixing screws to fix the lower polarizer.

The aperture lock (aperture) is located above the lower polarizer. By gently moving the adjustment handle, the aperture lock can be opened and closed freely to control the amount of light passing through. Narrowing the aperture reduces the brightness of the field of view.

The condenser is located between the aperture lock and the stage and consists of a set of lenses. It can highly condense the parallel polarized beam from the lower polarizer into a cone-shaped polarized beam, which can be pushed to the side when not in use. Equipped with a screw that raises and lowers the condenser system to adjust the position of the condenser. Some polarizing microscopes are equipped with two condensers with different numerical apertures (N.A.), which can be selected according to needs. The condenser of the BHSP polarizing microscope is equipped with a centering screw to adjust the center of the condenser.

The stage is a circular platform that can rotate horizontally, referred to as the stage. There is a 360° scale on the circumferential edge and a vernier scale attached, which can directly read the rotation angle of the stage (can read minutes). There is a circular hole in the center of the stage, which is a channel for light. There is a pair of spring clips next to the round hole to hold the sheet in place. There are fixing screws on the outer edge of the stage to fix the stage. Some microscopes are also equipped with rotating wheels that move the stage up and down. The stage of the BHSP polarizing microscope is equipped with a centering screw to correct the center of the stage. Rotating the coarse-motion and fine-motion focusing screws installed at the lower end of the lens arm can raise and lower the stage to adjust the focus.

The lens barrel is a long straight cylinder connected to the lens arm. Rotating the coarse-motion and fine-motion focusing screws at the connection with the lens arm can raise and lower the lens barrel to adjust the focus. The eyepiece is inserted into the upper end of the lens barrel, and the objective lens is installed at the lower end (mounted on the spring clip at the lower end of the lens barrel). The length from the upper end of the eyepiece to the place where the objective lens is mounted is called the mechanical tube length. The distance between the rear focal plane of the objective lens and the front focal plane of the eyepiece is called the optical tube length. The middle of the lens barrel is equipped with a Bertrand mirror, an upper polarizer and a test plate hole. Some also have aperture locks.

The lens tube of the BHSP polarizing microscope is a three-tube lens tube (Figure 3-4), which is composed of a tilted binocular lens tube and a straight tube. The binocular tube is used for binocular observation, and the straight tube is used for microphotography. The lower end of the tube is equipped with a 4-hole objective lens rotating disk, which can install 4 objective lenses with different magnifications at the same time. Next to each round hole for installing the objective lens, there are two objective lens centering screw holes for installing correction screws, which are used to correct the center of the objective lens. The entire lens barrel system is fixed, and the focus is adjusted with the help of the lifting and lowering of the stage.

Figure 3-4 Olympus BHSP polarizing microscope

1—The installation part of the camera device; 2—Eyepiece; 3—Eye distance adjustment plate; 4—Bernfield mirror; 5—Upper polarizer; 6—Test plate hole; 7—Objective lens rotating disk; 8—Objective lens center correction screw; 9—Objective lens; 10—Object stage; 11—Sheet clamp; 12—Object stage fixing screw; 13—Aperture adjustment handle; 14—lower polarizer; 15—aperture diaphragm adjustment ring; 16—lens holder; 17—brightness indicator light; 18—power switch; 19—brightness adjustment button; 20—halogen light source lamp; 21—object stage lifting micro Moving screw; 22—Object stage lifting and lowering coarse movement screw; 23—Intermediate component fixing screw; 24—Upper polarization rotation control screw; 25—Observation tube fixing screw; 26—Light path selection lever

Objective lens (connected to the objective lens ) is an important factor in determining the imaging performance of the microscope and consists of 1 to 5 groups of compound lenses. The lower lens is called the front lens, and the upper lens is called the rear lens. Generally speaking, the smaller the front lens and the longer the lens, the greater the magnification.

Each polarizing microscope is equipped with 5 objective lenses, namely 4×, 10×, 25×, 45×, and 63×. Each objective lens is marked with the magnification and numerical aperture (N.A.); some also state the optical tube length, cover glass thickness and front focal length. When in use, clamp the selected objective lens on the spring clip at the lower end of the lens barrel. The BHSP polarizing microscope comes with 5 objective lenses: 4×, 10×, 20×, 40× and 100× (oil immersion). When in use, install the objective lens on the rotating disk at the lower end of the lens barrel, and transfer the selected objective lens to the optical system.

The structure of the upper polarizer (analytical mirror) is the same as that of the lower polarizer. But the direction of its vibration surface is usually perpendicular to the direction of the vibration surface of the lower polarizer. Generally, the symbol "AA" indicates the direction of the vibration surface of the upper polarizer. The upper polarizer can be pushed in or out of the optical system. The upper polarizer of the BHSP polarizing microscope can also be rotated.

The Bertrand lens is located between the eyepiece and the upper polarizer. It is a small convex lens that can be pushed in and out (or rotated in and out) of the optical system. Some Bertrand mirrors can also move up and down and left and right. Some are also equipped with a locking aperture or a pinhole aperture. When observing the interference pattern of small minerals, narrowing the aperture or adding a pinhole aperture can block the interference of light from the surrounding minerals and make the interference pattern clearer.

Eyepiece (Eyepiece) Comes with 3 eyepieces, two 5× and 10× (one of which is equipped with a graduation ruler and one with a crosshair). The BHSP polarizing microscope has binoculars (10×).

The magnification of a microscope is equal to the product of the magnification of the eyepiece and the magnification of the objective lens. For example, if you use a 10× objective lens and a 10× eyepiece, the total magnification should be 10×10=100 times.

In addition to the above main components, there are also some accessories in the polarizing microscope.

Commonly used accessories include various color complementers, such as quartz wedges, gypsum test boards, mica test boards, etc., as well as mechanical tables and microscopic rulers. Some polarizing microscopes also have special accessories, such as light sources, vertical illuminators, rotating stages, microphotography equipment, etc.