Microscope Focal Length

A common microscopy term you may hear is focal length. The term focal length refers to the amount of distance required between the objective lens and the top of your object, in order to be able to view an image through the microscope that is in-focus. When using a biological microscope the higher your objective magnification, the shorter the focal length generally is. With the 4x objective there may be some space between the objective lens and your cover slip on your prepared slide. However, when using the 100x objective lens the objective will be almost touching the cover slip, due to a smaller focal length.


You can learn more about focal length as well as finite and infinity corrected optics here.