Definitions:

1. The lens or system of lenses in a telescope or microscope that is nearest the obeject being viewed. NOUN
   • He carefully cleaned the object glass to improve the image quality.
2. The primary lens at the front of an optical device, like a telescope or microscope, that gathers light from the object being observed and brings it into focus. NOUN
   • The telescope's object glass was fogged, making it hard to see the stars clearly.

Synonyms:

• eyepiece
• focal length
• objective lens