Draw a ray diagram of an astronomical telescope in the normal adjustment position. State two drawbacks of this type of telescope
The correct answer and explanation is :
Ray Diagram of an Astronomical Telescope in the Normal Adjustment Position:
In the normal adjustment position, an astronomical telescope uses two lenses: the objective lens (which has a larger diameter) and the eyepiece lens (which has a smaller diameter). Here’s how the ray diagram works in this configuration:
- Parallel Rays from a Distant Object: Light from a distant object enters the objective lens (the larger lens). Since the object is far away, the light rays coming from it are considered parallel.
- Focusing by the Objective Lens: These parallel rays converge at the focal point of the objective lens after passing through it. The focal length of the objective lens is crucial in determining the clarity and magnification.
- Eyepiece Lens: After passing through the focal point of the objective lens, the rays are then passed into the eyepiece lens. The eyepiece lens acts like a magnifying lens, bending the rays in such a way that the final image appears magnified.
- Final Image Formation: In the normal adjustment position, the eyepiece is positioned so that the image formed by the objective lens is at or near the focal point of the eyepiece lens. The observer views the magnified image through the eyepiece, which appears at a comfortable distance for the human eye.
Drawbacks of an Astronomical Telescope in the Normal Adjustment Position:
- Chromatic Aberration: Chromatic aberration occurs because lenses tend to bend different colors (wavelengths) of light by different amounts. In the case of an astronomical telescope, the objective lens (usually made of glass) may cause different colors of light to focus at slightly different points. This can lead to color fringes around bright objects, reducing the clarity and sharpness of the image.
- Field of View: In the normal adjustment position, the telescope often has a relatively narrow field of view. This is due to the high magnification achieved by the long focal length of the objective lens. A narrower field of view makes it challenging to track moving objects like planets or satellites and can make it harder to find and observe celestial objects.
300-word Explanation:
An astronomical telescope is designed to magnify distant objects, such as stars, planets, and other celestial bodies. It achieves this using two primary lenses: the objective lens and the eyepiece lens. The objective lens, which is positioned at the front of the telescope, has a long focal length and gathers light from the distant object, while the eyepiece lens has a shorter focal length and is used to magnify the image formed by the objective lens.
The normal adjustment position refers to the setup where the distance between the objective lens and the eyepiece lens is adjusted so that the image produced by the objective lens is at or near the focal point of the eyepiece lens. This allows the observer to see a magnified, upright image without the need for additional adjustments.
However, two common drawbacks of this type of telescope are chromatic aberration and a narrow field of view. Chromatic aberration is a result of the fact that lenses cannot focus all colors of light at the same point. As a result, the image may show color fringes around bright objects, reducing image quality. While this can be minimized with better lens materials or coatings, it remains a limitation of refracting telescopes.
The narrow field of view arises because high magnification, which is a feature of this configuration, reduces the area of sky visible through the telescope. This can make it harder to locate and track objects in the sky, especially moving ones like planets or comets. Consequently, astronomers need to make careful adjustments to keep the object in view, and it is often challenging for beginners.