What is the eyepiece (ocular lens) used for?

• A. A lens that forms the image on the retina.
• B. A filter used to adjust color balance.
• C. A mirror used to reflect light into the viewer’s eye.
• D. Eyepiece - a type of lens that is attached to a variety of optical devices such as telescopes and microscopes.

Answer: (D)

The eyepiece is the lens you look through to see the final, enlarged image. Its job is to magnify the image that the rest of the instrument forms so your eye can focus on it comfortably. In a microscope, the objective lens creates a small, enlarged image and the eyepiece makes it larger still for your eye to view. In a telescope, the objective or mirror forms an image, and the eyepiece enlarges that image so you can see it clearly. That’s why the description “a type of lens attached to optical devices such as telescopes and microscopes” is the best fit.

It isn’t the lens that forms an image on your retina, nor a color filter, nor a mirror.