Microscopes vs. Telescope

Difference Between Microscopes And Telescope

Microscopes

If you bring an object closer to a converging lens than the focal distance, you find that there is no longer any place where you can get a real image on the card. The reason is that rays from any point on the object have such a great spread that the lens cannot bring them together again on the other side. But if you look directly into the lens, you see a much enlarged image of the object. This makes a converging lens useful as a simple magnifier.

Rays coming from any point on an object are refracted by the lens. But they still have a slight spread after going through. These rays seem to have come from a point that is located by extending the final rays backward. Your eye sees the complete image, which is virtual and enlarged. It is also right side up, which is convenient when the lens is used as a magnifier.

Leeuwenhoek’s microscopes were one-lens magnifiers of this kind. They are called simple microscopes. To get better images and higher magnification, a combination of two converging lenses or sets of lenses must be used. A setup of this kind is called a compound microscope. That is the way all high-powered scientific microscopes are now made. A set of converging lenses, of very short focal distance, is mounted at the bottom end of a tube. This set of lenses is near the object that is being magnified. It is called the objective, or set of objective lenses. A second set of converging lenses, of moderate focal distance, is mounted at the upper end of the tube. This set of lenses forms the eyepiece, or ocular (ocular lenses). The tube can be moved slowly up or down by turning a knob.

An object that is to be examined is placed right under the objective. Then the tube is moved carefully up and down until the image is sharp. This image is virtual, and it is very much enlarged. It is also upside down and reversed from side to side. It seems to be located some distance below the objective.

Modern compound microscopes used by biologists, geologists, and engineers can magnify things as much as 1,500 times. This would make a single hair look as broad as the trunk of a tree. At high magnification, only a small part of an object may be seen at one time.

The Telescope

Telescopes are used to make distant objects appear nearer and larger. A refracting telescope has two sets of converging lenses, just as a microscope does. The important difference is that the objective system at the front end of the telescope has a very long focal distance, instead of a short one. As in the microscope, the final virtual image is upside down and reversed from side to side. This is troublesome for most uses of the telescope, and a third lens is sometimes put in to make things appear in their normal position. A better way of getting this result is to reflect the rays back and forth inside the instrument, using a pair of triangular pieces of glass, called prisms. At the same time this makes the instrument much shorter and more convenient to hold. A prism binocular is made up of a pair of such telescopes, one for each eye.

The biggest telescopes of all are the ones used in astronomy. These instruments must be able to take in enough light to make very faint or distant stars show up. In some cases, this means that the objective must be more than 1 meter in diameter. It is very difficult and expensive to grind and polish lenses of this size because the surfaces must be accurate to within about 1/400,000 centimeter. For this reason most of the very largest telescopes use a hollowed-out mirror in place of a set of objective lenses. Such an instrument is called a reflecting telescope.

If you bring an object closer to a converging lens than the focal distance, you find that there is no longer any place where you can get a real image on the card. The reason is that rays from any point on the object have such a great spread that the lens cannot bring them together again on the other side. But if you look directly into the lens, you see a much enlarged image of the object. This makes a converging lens useful as a simple magnifier.

Rays coming from any point on an object are refracted by the lens. But they still have a slight spread after going through. These rays seem to have come from a point that is located by extending the final rays backward. Your eye sees the complete image, which is virtual and enlarged. It is also right side up, which is convenient when the lens is used as a magnifier.

Leeuwenhoek’s microscopes were one-lens magnifiers of this kind. They are called simple microscopes. To get better images and higher magnification, a combination of two converging lenses or sets of lenses must be used. A setup of this kind is called a compound microscope. That is the way all high-powered scientific microscopes are now made. A set of converging lenses, of very short focal distance, is mounted at the bottom end of a tube. This set of lenses is near the object that is being magnified. It is called the objective, or set of objective lenses. A second set of converging lenses, of moderate focal distance, is mounted at the upper end of the tube. This set of lenses forms the eyepiece, or ocular (ocular lenses). The tube can be moved slowly up or down by turning a knob.

An object that is to be examined is placed right under the objective. Then the tube is moved carefully up and down until the image is sharp. This image is virtual, and it is very much enlarged. It is also upside down and reversed from side to side. It seems to be located some distance below the objective.

Modern compound microscopes used by biologists, geologists, and engineers can magnify things as much as 1,500 times. This would make a single hair look as broad as the trunk of a tree. At high magnification, only a small part of an object may be seen at one time.

The Telescope

Telescopes are used to make distant objects appear nearer and larger. A refracting telescope has two sets of converging lenses, just as a microscope does. The important difference is that the objective system at the front end of the telescope has a very long focal distance, instead of a short one. As in the microscope, the final virtual image is upside down and reversed from side to side. This is troublesome for most uses of the telescope, and a third lens is sometimes put in to make things appear in their normal position. A better way of getting this result is to reflect the rays back and forth inside the instrument, using a pair of triangular pieces of glass, called prisms. At the same time this makes the instrument much shorter and more convenient to hold. A prism binocular is made up of a pair of such telescopes, one for each eye.

The biggest telescopes of all are the ones used in astronomy. These instruments must be able to take in enough light to make very faint or distant stars show up. In some cases, this means that the objective must be more than 1 meter in diameter. It is very difficult and expensive to grind and polish lenses of this size because the surfaces must be accurate to within about 1/400,000 centimeter. For this reason most of the very largest telescopes use a hollowed-out mirror in place of a set of objective lenses. Such an instrument is called a reflecting telescope.

 

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