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The optical microscope uses visible light and a system of lenses to produce magnified images. Components common to such microscopes are the eyepiece, objective lens and illumination source.
The eyepiece, found at the top of the microscope, is a cylinder containing two or more lenses that brings the image to focus for the eye.
The objective lens is a cylinder containing one or more lenses that collects light from the sample. At the lower end of the microscope tube one or more objective lenses are incorporated into a circular nosepiece, which is rotated to select the required objective lens. On a standard compound optical microscope, there are three objective lenses: a scanning lens, a low-power lens and a high-power lens. Some compound microscopes have an oil immersion lens; this lens is used to keep refraction to a minimum.
The stage is a platform below the objective lens that supports the specimen being viewed. In the center of the stage is a circular hole through which light passes to illuminate the specimen.
The illumination source is located below the microscope’s stage. Most microscopes have controllable light sources that focus through an optical device called a condenser, with diaphragms and filters to manage the quality and intensity of the light.
Modern optical microscopes also may include transmission illumination, phase contrast microscopy and differential interference contrast microscopy, and digital cameras. Compound optical microscopes can be used to study thin specimens because of a limited depth of field.
The stereomicroscope is a type of optical microscope that uses two separate optical paths with two objectives and two eyepieces to provide slightly different viewing angles to the left and right eye. In this way it produces a 3-D visualization of the sample being examined. The stereomicroscope is often used to study the surfaces of solid specimens.
Unlike compound microscopes, illumination in a stereomicroscope most often uses episcopic, or reflected, illumination rather than diascopic, or transmitted, illumination. Episcopic illumination refers to light reflected from the surface of an object, while diascopic refers to light transmitted through an object. Use of reflected light from the object allows examination of specimens that would be too thick or otherwise opaque for compound microscopy. However, stereomicroscopes also are capable of transmitted light illumination as well.
Stereomicroscopes will either have fixed magnification or pancratic, or zoom, magnification. Fix magnification is achieved by a paired set of objective lenses with a set degree of magnification. Pancratic magnification means that the instrument is capable of a continuously variable degree of magnification across a set range. Zoom systems can achieve further magnification through the use of auxiliary objectives.
Stereomicroscopes can be fitted with CCD camera pickups, allowing digital display of images on a high-resolution LCD monitor.
The metallurgical microscope is an optical microscope that differs from other optical microscopes in its method of specimen illumination. Because metals are opaque substances, they must be illuminated by frontal lighting; therefore, the source of light is located within the microscope tube. To achieve this a plain glass reflector is installed in the tube.
The standard base has incident and transmitted illumination with adjustable intensity to provide correct lighting for most specimens. Alternatively, plain stands are available, supplied with cold lights or LED illuminators.
Trinocular models can be fitted with any of the digital or closed-circuit television (CCTV) cameras from the company, or conventional digital cameras. Software supplied with the company’s digital cameras allows images to be captured, manipulated, measured and reports generated. The connection of CCTV cameras to monitors is particularly appropriate for quality control environments.
Targets can be freely observed with the camera/lens unit either handheld or mounted in the multi-angle viewing stand. The observation can be performed at all angles without manipulating the target, helping to reduce the time required for observation and avoid the overlooking of defects.
A 3-D image composition mode allows the operator to obtain sharp images on specimens with large height differences that cannot be focused or observed easily with conventional microscopes. The microscope incorporates real-time camera shake correction, enabling observation free from the effects of environmental vibration. Halation removal eliminates 98% of reflectivity, and the image improvement function solves problems on displayed images caused by low contrast or illumination.
The microscope can perform real-time, onscreen measurement of the distance, radius, angle and area of the target. Data is processed in real-time. Transfer of image data to a PC is not required and data can be acquired while changing the visual field.
The microscope connects to PC and Mac computers via the USB2 port. It comes with free downloadable software to capture stills, video and time lapse, and the company offers three choices of measurement software all accurate to within 10 microns and pre-calibrated for available lenses.
The microscope uses modular lenses, ranging from 0 to 10X, 30X, 50X, 100X, 200X, 400X and 1,000X. Adapters allow the microscope to be connected to an analog microscope if the operator prefers to use his own optics and capture images to a desktop. The company also offers a borescope adapter.
The microscope is a USB video class device, meaning that the driver is part of the Windows and Mac operating system. Because of this, it can be used without software.
Each microscope has ergonomically positioned controls and a Siedentopf viewing head; 30-watt vertical Koehler illuminator with auto voltage sensing power supply; 30-watt transmitted Koehler illuminator with auto voltage sensing power supply; brightfield reflected light and brightfield transmitted light observation modes; and optional ergonomic binocular viewing head.
The unit consists of a 20X monocular scope with reticle, illuminator, stabilizer stand and a calibration stage micrometer. The scope contains high-quality optics that produce a sharp erect image.
The scope does not need to be focused by the operator because all adjustments are fixed at the factory. The reticle and the object observed are always in focus. There are no external moving parts, which helps make the unit tamper proof.
The lower part of the battery-operated scope contains a replaceable, clear plastic tube to help illuminate the object. A removable LED illuminator is used when more illumination is required. The end of the tube has a hardened metal ring to prevent wear and maintain accuracy. The plastic tube permits insertion and observation into small cavities. A metal disk stand is included for stabilizing the scope when it is used on larger flat surfaces.
A stage micrometer, traceable to NIST, also is available. This artifact is a clear glass disk with a durable chrome image mounted in a round metal frame used to check the calibration of the scope. The check is done quickly without the hassle of sending the scope to a calibration laboratory.
By providing a live image in high SXGA resolution, it facilitates precise specimen positioning and focusing. The camera requires a single shot to capture a complete 7-megapixel image, including objects in motion or those involving flash illumination. The camera’s integrated shutter allows it to be triggered directly and precisely, which is important for integration into automated process sequences or applications involving motorized stage movement.