What does the eyepiece lens do in a refracting telescope?

• A. Collects light
• B. Focuses light
• C. Similar to a magnifying glass - enlarges the image
• D. Reflects light

Answer: (C)

The eyepiece acts as a magnifier for the image formed by the objective. In a refracting telescope, the objective lens collects light and creates a real image at its focal plane. The eyepiece is placed so that this real image sits at or near its own focal point, and then its lenses magnify that image so your eye sees a larger, easily focused view. This is why it’s like using a magnifying glass—the eyepiece increases the angular size of the image you look at, rather than being the part that collects light or sends it to a mirror. The magnification roughly equals the focal length of the objective divided by the focal length of the eyepiece (M ≈ fo/fe).