Eyepiece or Ocular is what you look through at the top of the microscope. Typically, standard eyepieces have a magnifying power of 10x. Optional eyepieces of varying powers are available, typically from 5x-30x.

Objective Lenses are the primary optical lenses on a microscope. They range from 4x-100x and typically, include, three, four or five on lens on most microscopes. Objectives can be forward or rear-facing.

As a boater and general aviation pilot I wouldn't call light houses at all obsolete, they provide additional situational awareness and backup in the event of the failure of other systems such as GNSS (GPS). In Australia at least it was not uncommon to have "lighthouses" at most medium to small aerodromes as an additional aid to navigation although these are slowly disappearing. Within 40NM, I'd still pick an airfield light house over GNSS if I had the choice.

Fresnel continued to modify the lens for several years. His final design, which he completed in 1825, could spin 360 degrees and was the first so-called fixed/flashing lens. It produced a fixed light followed by a brilliant flash followed by another fixed light.

Nosepiece houses the objectives. The objectives are exposed and are mounted on a rotating turret so that different objectives can be conveniently selected. Standard objectives include 4x, 10x, 40x and 100x although different power objectives are available.

Fresnel’s analysis of contemporary lighthouse technology found the lenses were so thick that only half the light produced shined through.

The lenses came in several sizes, known as orders. The largest order, the Hyper-Radial, had a 1,330-millimeter diameter. The smallest, the eighth order, had a 75-mm diameter and could be found in lighthouses on bays and rivers.

Because of increasing complaints from French fishermen and ship captains about the poor quality of the light emanating from lighthouses, in 1811 the French Commission on Lighthouses established a committee under the authority of the Corps of Bridges and Roads to investigate how lighthouse illumination could be improved.

In 1823 the French Commission on Lighthouses committee approved the use of the Fresnel lens in all lighthouses in France. That same year, the first one was installed in the Cordouan Lighthouse, in southwestern France. The lens eventually was adopted in other countries. By the 1860s, all the lighthouses in the United States had been fitted with a Fresnel lens, according to the Smithsonian Institution.

Joanna Goodrich is the associate editor of The Institute, covering the work and accomplishments of IEEE members and IEEE and technology-related events. She has a master's degree in health communications from Rutgers University, in New Brunswick, N.J.

How does aFresnel lenswork

Stage is where the specimen to be viewed is placed. A mechanical stage is used when working at higher magnifications where delicate movements of the specimen slide are required.

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Coarse and Fine Focus knobs are used to focus the microscope. Increasingly, they are coaxial knobs - that is to say they are built on the same axis with the fine focus knob on the outside. Coaxial focus knobs are more convenient since the viewer does not have to grope for a different knob.

A clock mechanism, which had to be wound by hand every few hours, was used to revolve the metal frame around the lamps to produce unique light patterns for specific lighthouses. A lighthouse could send out a flash regularly every 5 seconds, for example, or it could have a 10-second period of darkness and a 3-second period of brightness. Captains counted the number of flashes sent out by a lighthouse to calculate their ships’ location.

Iris Diaphragm controls the amount of light reaching the specimen. It is located above the condenser and below the stage. Most high quality microscopes include an Abbe condenser with an iris diaphragm. Combined, they control both the focus and quantity of light applied to the specimen.

Eyepiece Tube holds the eyepieces in place above the objective lens. Binocular microscope heads typically incorporate a diopter adjustment ring that allows for the possible inconsistencies of our eyesight in one or both eyes. The monocular (single eye usage) microscope does not need a diopter. Binocular microscopes also swivel (Interpupillary Adjustment) to allow for different distances between the eyes of different individuals.

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A high power or compound microscope achieves higher levels of magnification than a stereo or low power microscope. It is used to view smaller specimens such as cell structures which cannot be seen at lower levels of magnification. Essentially, a compound microscope consists of structural and optical components. However, within these two basic systems, there are some essential components that every microscopist should know and understand. These key microscope parts are illustrated and explained below.

In 1822 French civil engineer Augustin-Jean Fresnel (pronounced “Frey Nel”) invented a new type of lens that produced a much stronger beam of light. The Fresnel lens is still used today in active lighthouses around the world. It also can be found in movie projectors, magnifying glasses, spacecraft, and other applications.

Condenser is used to collect and focus the light from the illuminator on to the specimen. It is located under the stage often in conjunction with an iris diaphragm.

Fresnel lens lighthousehistory

I've been looking for the formulas to used to calculate the focal lengths of the different order lights. My understanding is that these are differential equations, but that's as far as I've been able to get (since I can't read French, Fresnel's writings are inaccessible). If anyone has a clue about these formulas, please reply here or email me at

If you are interested in submitting a proposal, do so here.The History Center is funded by donations to the IEEE Foundation. For more on the history of lighthouse technology, visit the U.S. National Park Service, Ponce Inlet Lighthouse and Museum, and American Physical Society websites.

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Fresnel’s technical achievement is worthy of being named an IEEE Milestone, according to the IEEE History Center, but no one has proposed it yet. Any IEEE member can submit a milestone proposal to the IEEE History Center. The Milestone program honors significant accomplishments in the history of electrical and electronics engineering.

With the invention of modern navigational tools, the lighthouse has become largely obsolete for maritime safety. But the lens invented for it lives on in side mirrors used on trucks, solar panels, and photographic lighting equipment.

The mirrors were not very effective, though, and the lenses were murky. The light was difficult to see from a distance on a clear night, let alone in heavy fog or a storm.

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Illuminator is the light source for a microscope, typically located in the base of the microscope. Most light microscopes use low voltage, halogen bulbs with continuous variable lighting control located within the base.

He decided he could do better using his wave theory. His design consisted of 24 glass prisms of varying shapes and sizes arranged in concentric circles within a wire cage. The prisms, placed both in front of and behind four oil lamps, replaced both the mirror and the glass lens of the previous method. Prisms at the edge of the circle refract light slightly more than those closer to the center, so the light rays all emerge in parallel. The design could focus nearly 98 percent of the rays generated by the lamps, producing a beam that could be seen more than 32 kilometers away.

Ships today use satellite-based radio navigation, GPS, and other tools to prevent accidents. But back at the beginning of the 19th century, lighthouses guided ships away from rocky shores using an oil lamp placed between a concave mirror and a glass lens to produce a beam of light.

Stage Clips are used when there is no mechanical stage. The viewer is required to move the slide manually to view different sections of the specimen.

One member of that committee was Fresnel, who worked for the French civil service corps as an engineer. He had considerable expertise in optics and light waves. In fact, in 1817 he proved that his wave theory—which stated the wave motion of light is transverse rather than longitudinal—was correct. In transverse waves, a wave oscillates perpendicular to the direction of its travel. Longitudinal waves, like sound, oscillate in the same direction that the wave travels.