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The purpose of a telescope is to increase the angle at which a distant object is placed to subtend at the eye, creating the illusion that the object is larger or closer to the eye. Rays from any point on a very distant object, such as a star that is effectively at infinity, are a sensible parallel when they reach the telescope. As a result, a genuine image I is produced in the focal plane of the objective. The focal plane of the objective is the same as the focal plane of the eye lens. As a result, the image I serve as an object for the eye lens, and a final virtual, highly magnified image at infinity in normal adjustment is created. The magnification power of the telescope is clearly derived from the fact that the final image at infinity occupies a significantly larger angle in the eye than the distant object. It makes no difference whether the final image is inverted for astronomical reasons. The objective lens should have a long focal length j, whereas the eye lens should have a short focal length I. In this regard, a telescope differs from a compound microscope.
The objective produces a true and inverted image of the distant object at its focal plane. The distance between the eyepiece and the objective is adjusted until the final image is generated at the shortest distance vision. If the position of the eye is changed to the point where the final image is generated at infinity. To increase the magnification power of an astronomical telescope in a typical adjustment, the focal length of the objective lens should be large, while the focal length of the eye lens should be small.
The objective lens focuses light rays to produce an accurate image of a distant object. When light rays cross each other while passing through the lens, an image is formed in the same plane as the objective lens’s primary focus. The eyepiece magnifies the true image for the observer looking through the telescope. This magnified representation of the object is known as a virtual image because the rays emanating from the eyepiece appear to be coming from behind the eyepiece. The virtual image is inverted in comparison to the distant object.
Overview
When examining the details of an object, it is instinctive to bring it as close to the eye as possible. The greater the angle that the object subtends at the eye, the larger the object appears. However, if an object is brought too close, the eye can no longer form a clear image. The use of a magnifying lens between the observer and the object creates a “virtual image” that can be viewed comfortably. The magnifier should be placed directly in front of the eye to obtain the best image possible. The object of interest is then brought into close proximity to the eye until a clear image of the object is obtained.
The geometry of the optical system is related to the magnifying power, or the extent to which the object being viewed appears enlarged, and the field of view, or the size of the object that can be viewed. A working value for a lens’ magnifying power can be calculated by dividing the shortest distance of distinct vision by the focal length of the lens, which is the distance from the lens to the plane where the incoming light is focused.
A simple microscope is essentially a magnifying glass with a double convex lens and a short focal length. The hand lens and reading lens are two examples of this type of instrument. When an object is kept close to the lens, its primary focus produces an image that is erect and larger than the original object. The formed image is virtual and cannot be projected on a screen in the same way that a real image can.
Astronomical Telescope and magnifying powers
A telescope is a type of optical instrument used to see distant objects. There are two kinds of telescopes:
1. Telescope for astronomical observations
2. Galilean or terrestrial telescope
Telescope for Astronomy
An astronomical telescope is an optical instrument used to magnify images of distant celestial bodies such as stars, planets, satellites, and galaxies. An astronomical telescope’s final image is always virtual, inverted, and magnified.
When an object to be magnified is placed at a great distance from the objective lens of a telescope, a virtual, inverted, and magnified image of the object is formed at the shortest distance of distinct vision from the eye held close to the eyepiece.
Magnification can take place in lenses, telescopes, microscopes, and even slide projectors. Simple magnifying lenses are biconvex, which means they are thicker in the centre than they are at the edges. One of the first instruments used to magnify an object was the magnifying glass. Magnification refers to the process of scaling up images in order to see fine details by increasing image resolution. There are two kinds of magnification: linear and angular.
Linear or transverse magnification – This occurs when real images, such as those projected on screens, are magnified.
Angular magnification – This type of magnification is found in optical instruments that have an eyepiece. The angle subtended by the object at the focal point determines the size of the image.
The operation of an astronomical telescope
It consists of two lenses: the objective lens O with a long focal length and a large aperture, and the eyepiece E with a short focal length and a small aperture. The magnification is caused by refraction through these lenses. During normal telescope adjustments, the final image is created at infinity. At its focal plane, the objective produces a true and inverted image of the distant subject. When the distance between the eyepiece and the objective is changed, the final image is generated with the least amount of distance vision. To create the final image at infinity, the eye location is adjusted.
When the final image is formed at or near the distance of distinct vision (D),
m = fo/fe {1+ (D/fe)}
where fo and fe are the objective and eyepiece focal lengths, respectively.
Telescope length (L) = (fo + ue) where ue is the object’s distance from the eyepiece
m = fo/fe when the final image is formed at infinity
Telescope length (L) = fo + fe
Fo should be large for a higher magnifying power, and fe should be small.
FAQs
What are the various kinds of astronomical telescopes?
Telescopes are classified into three types. There are three types of telescopes: refracting telescopes, Newtonian telescopes, and Schmidt-Cassegrain telescopes.
What is an astronomical telescope's magnification power?
An astronomical telescope has a magnifying power of 5 and an eyepiece focal power of 10 diopters.
What is the highest magnification?
When combined with a 10x eyepiece, the oil immersion objective lens provides the most powerful magnification, with a total magnification of 1000x.
