Optical/light microscopes use the visible or near-visible portion of the electromagnetic spectrum to magnify images of objects. There are two basic types of devices. Stereomicroscopes use two light paths for three-dimensional (3D) viewing.
They provide high depth perception, low resolution, and low magnification. Some devices include a built-in light source and zoom capabilities. Compound microscopes are optical / light microscopes that use a single light path. Both monocular and binocular versions are available. Typically, compound microscopes are used for viewing very small specimens such as cells, pond life samples, and other microscopic life forms. They have low depth perception, but high resolution and magnification.
There are three grades of optical / light microscopes: student, benchtop, and research. Student microscopes are the smallest and least expensive type of device. They are capable of advanced techniques and are designed for bright field, dark field, and phase contrast examinations. Benchtop microscopes provide a range of examination techniques, but can perform only a few methods at one time. Research microscopes are large devices that weigh between 30 kg and 50 kg and contain complex optical, mechanical, and electronics systems. These devices include multiple cameras and can perform the widest range of simultaneous examinations. Many research microscopes contain built-in computers that control the cameras and functions such as focus management and image processing.
Selecting optical / light microscopes requires an analysis of performance specifications and features. Performance specifications include total magnification, resolution, field of view, working distance, and number of objective lenses. Some optical / light microscopes can be controlled or monitored via a computer interface. Others include a digital display or application software for analyzing images. Devices that are equipped with mechanical stages can hold specimen slides firmly in place or allow the rotation of slides. Spring loaded front lenses prevent damage to objects that are driven accidentally onto the surfaces of slides. Oil immersion lenses are sealed and designed for immersion in an oil-based medium. Optical / light microscopes with a variable working distance allow the imaging of specimens through glass cover slips of variable thickness.
Optical / light microscopes differ in terms of eyepiece style. Monocular eyepieces have only one objective and one body tube. Binocular microscopes are fitted with double eyepieces to reduce user eyestrain and muscular fatigue, problems that may result from high-power monocular microscopy. Dual head microscopes include a vertical eyepiece lens and an eyepiece angled at 45° on the side. They allow two users to view a sample at the same time. Trinocular microscopes have a vertical tube at the top and regular binocular eyepieces at 30?. Typically, the vertical tube is used by a digital camera or a second observer.
There are many applications for optical / light microscopes. Biological and life science microscopes transmit light or use environmental scanning electron microscopy (SEM). Gemological devices use polarized light with lower magnifying powers to produce sharp, bright images in a wide field of view. Measuring microscopes are used to measure the dimensional properties of tools and provide lower magnifying powers to allow for brighter, sharper images combined with a wide field of view. Medical and forensic microscopes are usually hands-free and binocular. Some optical / light microscopes are used to examine the layers in semiconductor wafers and fabricated integrated circuit (IC) components. These devices provide superior precision and throughput.