what is the distance between objective and eye lens of telescope in normal adjustment?

The distance between the objective lens and the eye lens of a telescope in normal adjustment is typically referred to as the "focal length" of the telescope. In a standard refracting telescope, this distance is equal to the sum of the focal lengths of the objective lens and the eyepiece lens. To understand this better, let’s break it down step by step.

Understanding Telescope Components

A telescope primarily consists of two lenses: the objective lens and the eyepiece lens. The objective lens is responsible for gathering light and forming an image of a distant object, while the eyepiece lens magnifies that image for the viewer.

Focal Lengths Explained

The focal length of a lens is the distance from the lens to the point where it focuses light. For telescopes:

• Objective Lens: This lens usually has a longer focal length, which allows it to collect light from distant objects.
• Eyepiece Lens: This lens has a shorter focal length, which is used to magnify the image created by the objective lens.

Calculating the Distance

In normal adjustment, the distance between the objective and the eyepiece is equal to the sum of their focal lengths. If we denote the focal length of the objective lens as f_o and the focal length of the eyepiece lens as f_e, the distance D can be expressed as:

D = f_o + f_e

Example Calculation

Let’s say the focal length of the objective lens is 1000 mm and the focal length of the eyepiece lens is 10 mm. The distance between the two lenses in normal adjustment would be:

D = 1000 mm + 10 mm = 1010 mm

Practical Implications

This distance is crucial for achieving a clear and focused image. If the lenses are too far apart or too close together, the image may appear blurry or distorted. Therefore, understanding this distance helps in setting up the telescope correctly for optimal viewing.

Final Thoughts

In summary, the distance between the objective and eyepiece lenses in a telescope during normal adjustment is the sum of their respective focal lengths. This relationship is fundamental to the design and function of telescopes, ensuring that they provide clear and magnified images of celestial objects.