Objective Lens in Astronomical Telescopes

The objective lens is the primary lens in an astronomical telescope that faces the distant object. Its main purpose is to gather as much light as possible from the object and form a bright, real, and inverted image inside the telescope tube. To achieve this light-gathering and image-forming capability, a convergent lens (also known as a convex lens) is used. Its converging power helps focus the parallel light rays from distant objects to a point.

Eyepiece Lens in Astronomical Telescopes

The eyepiece lens is the lens closest to the observer's eye. It takes the real, inverted image formed by the objective lens and magnifies it to produce a final virtual, inverted image that the observer can see. For a simple astronomical telescope, a convergent lens is typically used as the eyepiece. It acts like a magnifying glass, enlarging the intermediate image formed by the objective.

Lens Combination for Simple Telescopes

Based on the functions required:

• The objective needs to gather light and form a real image, requiring a convergent lens.
• The eyepiece needs to magnify the real image, also typically requiring a convergent lens in a simple refracting design.

Therefore, the combination used is a convergent lens for the objective and a convergent lens for the eyepiece.

Analysis of Options

Let's look at the given options:

• Option 1: convergent and divergent - Incorrect for a simple astronomical telescope.
• Option 2: divergent and divergent - Incorrect.
• Option 3: divergent and convergent - Incorrect.
• Option 4: convergent lens and a convergent lens - Correct.

Thus, the correct setup for a simple astronomical telescope uses two convergent lenses.