A telescope is said to be in normal adjustment when the

Analyze the question: "Normal adjustment" describes how the two lenses of an astronomical telescope are positioned relative to each other, not the sizes of their focal lengths.

Concept: An astronomical (refracting) telescope has two converging lenses:

• The objective, with a long focal length (f₀), forms a real image of a distant object at its focal point.
• The eyepiece, with a short focal length (fₑ), acts as a magnifier for that image.

In normal adjustment, the final image is formed at infinity. This is the most relaxed way to view with the eye, because the eye muscles are not strained. For this to happen, the image formed by the objective must lie exactly at the focal point of the eyepiece. Since that image is also at the focal point of the objective, the two focal points coincide.

Solution:

• Distance between the lenses: L = f₀ + fₑ
• Angular magnification: M = f₀ / fₑ

Checking the options:

• A. f₀ > fₑ is true for a telescope in general, but it doesn't define normal adjustment.
• B. This is wrong, because the eyepiece has the shorter focal length.
• C. This is wrong, because equal focal lengths would give M = 1.
• D. The objective's focal point coincides with the eyepiece's focal point. This is the correct condition, and it produces the final image at infinity.

Answer: D

Tip: Remember "Normal = Next to infinity": normal adjustment means the final image is at infinity, the lenses are separated by f₀ + fₑ, and the focal points coincide.