This short animation illustrates how oil immersion works.

Check out our other microscope training videos and eLearning tools:
• "Use and Care of a Microscope" (   • How to Use and Care for a Microscope  )

• "Microscope for Beginners Q&A" (   • Microscope for Beginners  Questions ...  )

• Virtual Microscope eLearning (http://www.ncbionetwork.org/education...)

We need to use oil to see at the highest magnification. Without getting too technical there's an air gap between the top of the coverslip and the front lens. This gap actually causes light to bend or refract. These scattered rays of light don't travel through the objective lens and are lost to the image. Oil affects the light a lot like glass does, so we replace the air gap with oil and suddenly we're able to see higher resolution images.