An endoscope can consist of
• a rigid or flexible tube
• a light delivery system to illuminate the organ or object under inspection. The light source is normally outside the body and the light is typically directed via an optical fiber system
• a lens system transmitting the image to the viewer from the objective lens to the viewer, typically a relay lens system in the case of rigid endoscopes or a bundle of fiber optics in the case of a fiberscope
• an eyepiece
• an additional channel to allow entry of medical instruments or manipulators
Before the fiber optics endoscope was invented, they used a semi-flexible tube with a tiny camera attached at the tip to detect stomach ulcers and stomach cancer in its early stage. The first fiber optics endoscope was invented in 1963/64. It paved the way for key-hole surgery. A “fibroscope” is actually a bundle of glass fibres that is able to channel light from one end to the other through total internal reflection.
However, the fiber optics endoscope was not the latest version of endoscope invented. The Rod-lens Endoscopes was one of the more advanced versions. This is because there were many difficulties while using the fiber optics endoscope and 50000 fibres give only a 50000pixel image, therefore, if any fiber breaks, that means that the image would decrease in pixels and quality. After continued flexingm more and more fibres would break and eventually, the whole bundle has to be replaced and it is very expensive. Therefore, the elegant solution that Hopkins produced (in the late 1960s) was to fill the air-spaces between the 'little lenses' with rods of glass. These fitted exactly the endoscope's tube - making them self-aligning and requiring of no other support and allowed the little lenses to be dispensed with altogether. The rod-lenses were much easier to handle and utilized the maximum possible diameter available. With the appropriate curvature and coatings to the rod ends and optimal choices of glass-types, all calculated and specified by Hopkins, the image quality was transformed - even with tubes of only 1mm. in diameter. With a high quality 'telescope' of such small diameter, the tools and illumination system could be comfortably housed within an outer tube. Once again, it was Karl Storz who produced the first of these new endoscopes as part of a long and productive partnership between the two men. Whilst there are regions of the body that will forever require flexible endoscopes (principally the gastrointestinal tract), the rigid rod-lens endoscopes have such exceptional performance that they are to this day the instrument of choice and in reality have been the enabling factor in modern key-hole surgery. (Harold Hopkins was recognized and honoured for his advancement of medical-optic by the medical community worldwide. It formed a major part of the citation when he was awarded the Rumford Medal by the Royal Society in 1984.)
Adapted from Wikipedia.
Thursday, July 14, 2011
How are mirages formed?
Mirages are a result of refraction. They are often sighted in deserts. Some people might call it hallucination but there is a reason why there can be an “oasis” appearing in the middle of a desert when there actually in not one. I have been wondering how they are formed and I did not really understand the explanation. However, now that we have learnt on refraction, I now can relate a little better.
Mirages are formed when light rays are bent as the light ray passes through air layers with different densities. This is actually refraction. The reason why mirages can be form due to varying densities of air is because the index of refraction for air varies with the density of the air. Air density is dependent on its pressure, temperature and water vapour content. Air density is also proportional to its pressure, which means that density increases as pressure increases and it is also inversely proportional to its temperature, which means that density decreases as temperature increases.
This image is trying to express that the “oasis” that the eye apparently sees is actually a mirage. The mirage of the oasis is actually the image of the bluish sky being strongly refracted by the hot air near the surface so that it appears to be water lying on the surface. This is also known as an inferior mirage as the warm air is below the cool air.
The opposite of an inferior mirage is a superior mirage. It occurs when the cool air is under the warm air. It happens very often at sea , or over ice and snow surfaces. When cold air lies below the warm air, the light rays from the object is bent towards our eyes, tricking it into thinking that the object is higher or taller in appearance than it actually is. It can also make objects appear as though it is floating. Here are some examples:
Sources, Help and Images:
http://www.islandnet.com/~see/weather/elements/mirage1.htm
Mirages are formed when light rays are bent as the light ray passes through air layers with different densities. This is actually refraction. The reason why mirages can be form due to varying densities of air is because the index of refraction for air varies with the density of the air. Air density is dependent on its pressure, temperature and water vapour content. Air density is also proportional to its pressure, which means that density increases as pressure increases and it is also inversely proportional to its temperature, which means that density decreases as temperature increases.
This image is trying to express that the “oasis” that the eye apparently sees is actually a mirage. The mirage of the oasis is actually the image of the bluish sky being strongly refracted by the hot air near the surface so that it appears to be water lying on the surface. This is also known as an inferior mirage as the warm air is below the cool air.
The opposite of an inferior mirage is a superior mirage. It occurs when the cool air is under the warm air. It happens very often at sea , or over ice and snow surfaces. When cold air lies below the warm air, the light rays from the object is bent towards our eyes, tricking it into thinking that the object is higher or taller in appearance than it actually is. It can also make objects appear as though it is floating. Here are some examples:
http://www.islandnet.com/~see/weather/elements/mirage1.htm
Refraction and Total Internal Reflection
This is one of the subtopics of Light. I felt this part a little confusing as it was challenging to draw the total internal reflection and the refraction digrams.
Refraction of Light
When light strikes an opaque reflecting surface such as a irror, most of the light is reflected. Some light, however, is absorbed by the surface.
At the air-glass surface (or interface), light is partially reflected off the surface and partially transmitted through the medium. THe reflected light follows the laws of reflection studied earlier. The light that is transmitted through the medium as it travels from one optical medium (air) into another (glass). This bending effect of light is known as refraction.
The amount of refraction depends on the optical density of the medium. Here we define optical density to be a measure of the exten to which a substance transmit visible light. The higher the opticaldensity of a medium, the lower the tranmittance, thus the greater is the refraction of light in it. For example, glass is an optically denser medium than water. If a light ray were to enter glass from air and water from air respectively, keeping all other parameters constant, the ray would bend more in glass than in water.
However, that the bending only occurs at the interface. Whithin the same medium, light still travels in a straight line.
How will light behave when it enters a different optical medium?
When a light ray strikes perpendically to the surface of an opticalmedium e.g. glass, it passes straight through without refraction.
This is because when it travels from air into glass, its angle of incidence is zero, thus, its angle of refraction is also zero. Even though light is not bent, its speed stilldecreases when it enters the optically denser medium, glass.
The angle of refraction is always smaller than the angle of incidence. This means that when a light ray travels from an optically less dense medium into an optically denser medium at an angle, it is always refracted towards the normal as light travels slower in the optically denser medium.
Refraction of Light
When light strikes an opaque reflecting surface such as a irror, most of the light is reflected. Some light, however, is absorbed by the surface.
At the air-glass surface (or interface), light is partially reflected off the surface and partially transmitted through the medium. THe reflected light follows the laws of reflection studied earlier. The light that is transmitted through the medium as it travels from one optical medium (air) into another (glass). This bending effect of light is known as refraction.
The amount of refraction depends on the optical density of the medium. Here we define optical density to be a measure of the exten to which a substance transmit visible light. The higher the opticaldensity of a medium, the lower the tranmittance, thus the greater is the refraction of light in it. For example, glass is an optically denser medium than water. If a light ray were to enter glass from air and water from air respectively, keeping all other parameters constant, the ray would bend more in glass than in water.
However, that the bending only occurs at the interface. Whithin the same medium, light still travels in a straight line.
How will light behave when it enters a different optical medium?
When a light ray strikes perpendically to the surface of an opticalmedium e.g. glass, it passes straight through without refraction.
This is because when it travels from air into glass, its angle of incidence is zero, thus, its angle of refraction is also zero. Even though light is not bent, its speed stilldecreases when it enters the optically denser medium, glass.
The angle of refraction is always smaller than the angle of incidence. This means that when a light ray travels from an optically less dense medium into an optically denser medium at an angle, it is always refracted towards the normal as light travels slower in the optically denser medium.
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