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Vision Enhancement
Binoculars are devices used to see distant objects. People used to use “binoculars” by holding two telescopes next to each other. People, however, eventually made the binoculars we use today.
There are three types of binoculars, the primitive Galilean binoculars, the contemporary roof-prism binoculars, and the bulky Porro-prism.
The Galilean binoculars are named after the famous Italian physicist Galileo Galilei. They are often called opera glasses, and are the cheapest and least satisfactory binoculars. They can only work
adequately at very low magnification (four times of less), and have a very small field
of view. These binoculars works with only lenses and no prisms. It has a concave lens for its eyepiece, and a convex lens for the objective
lens.
Obtained from www.epinions.com/
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Obtained from Encarta Encyclopedia 2004 Click on the image to view the full-size image |
When you think of binoculars, you think of the Porro-prism kind. These were named after a very obscure Italian scientist. His name might have been Ignatz Porro, but no one is sure. Porro-prism lenses have two prisms to make the length of the binoculars seem longer. In this case, the prisms act as mirrors and bend the light, therefore making the binocular tube seem longer.
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Obtained from www.monkoptics.co.uk |
The roof-prism binoculars look like the cheaper Galilean binoculars and are named after the shape of the prism inside it. They have four mechanical highlights: they are lighter than their Porro-prism counterparts, they tolerate rough treatment better than Porro-prism binoculars since the lenses and prisms are arranged more simply, they are less likely to fog on the inside, and they feel better when gripped, compared to Porro-prism binoculars.
There are down sides to roof-prisms too. The images formed by roof-prisms will not be, in general, as sharp as
Porro-prism binoculars. To equal the sharpness of Porro-prisms, roof prisms must be manufactured and aligned 300 times more accurately.
Telescopes are the longer,
more powerful version of binoculars. They are used to see things that are very far away, like stars.
Telescopes collect and focus light using lenses or mirrors. Optical telescopes
are categorized into two groups: refractors and reflectors. Refractors are telescopes
that use lenses, reflectors are ones using curved mirrors.
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Obtained from Encarta Encyclopedia 2004 Click on the image to view the full-size image |
Refracting telescopes have two convex lenses. The objective lens (the lens of the
telescope
where light is received) concentrates the star light to a point called the focus. This is the place where the star can be seen or photographed.
There
are three kinds of reflecting telescopes: the Newtonian reflector, the Cassegrain reflector, and the Nasmyth reflector. The most widely used reflector is the Newtonian reflector.
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Obtained from Encarta Encyclopedia 2004 Click on the image to view the full-size image |
The Newtonian reflector is named after an English physicist, Sir Isaac Newton. It has a big bowl-shaped mirror at the end of the telescope tube
to reflect the light back and to converge it, and another small diagonal mirror to bend the light 90 degrees to the eyepiece located at the side of the telescope.
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Obtained from www.oldham-optical.co.uk |
The Cassegrain reflector is named after the French astronomer Guillaume Cassegrain. It is slightly different from the Newtonian reflector, having a small mirror placed parallel to the large mirror (instead of being diagonal to the large mirror). The light comes out from the end of the tube opposite to the side where the target object is.
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Obtained from www.oldham-optical.co.uk |
The Nasmyth reflector is named after the Scottish engineer James Nasmyth. It is a derivative of the Cassegrain reflector and has another mirror placed diagonally. This mirror is placed like inside the Newtonian reflector. It also has two straight mirrors, like the Cassegrain reflector.
The more light the telescope can collect, the fainter and the more distant the objects it can detect. Bigger lenses or mirrors will allow the telescope to collect more light. It is difficult, however, to make large lenses because they can be only supported around the rim. Big lenses sag because of their weight, generating distorted images. Big mirrors are easier to make because they can be supported over their entire back surface. For this reason, the biggest telescopes in the world are all reflecting telescopes.
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Obtained from www.microscopeworld.com |
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Obtained from Encarta Encyclopedia Click on the image to view the full-size image |
Microscopes are devices that magnify the world to let us see stuff that are too small to see. The microscope uses two lenses to magnify the object, the eyepiece lens and the objective lens. They are both convex lenses. The objective lens forms an upside-down and magnified real image of the object.
The real image part means light actually passes through the place where the image is displayed. The eyepiece magnifies this image, and creates a virtual image (this image does not have light passing through it).
In other words, a microscope works almost like a refracting telescope, with just a few differences: microscopes have a much smaller objective lens since it gathers light from a small slide rather than a distant star. Also, the microscope tube is not as long as the telescope tube. A magnifying glass is really simple. It’s just a convex lens inside a frame.