Interactive Tutorials - Spinning Disk Fundamentals

Interactive Tutorials

Basic Microscopy

Fixed Tube Length Microscope Conjugate Field Planes

The total magnification of the microscope can be determined by considering properties of the objective and eyepieces. Objectives are corrected for a particular projection distance, which is specific to the magnification and is approximately equal to the optical tube length. In a fixed tube length microscope, this projection distance is about 160 millimeters. Therefore, a 8-millimeter focal length objective would have a lateral magnification of about 20x (160/8) with a corresponding longitudinal magnification of 400x (20 × 20). The geometrical relationship between image planes in the optical microscope is explored in this tutorial. In all of the imaging steps, with the exception of Image Plane (3'), the image is real and inverted.

For visual observation, the eyepiece magnification is assumed to be unity when a specimen (or image) is placed at a distance of 250 millimeters from the eye of the observer. In this regard, an eyepiece having a focal length of 25 millimeters would have a magnification value of 10x (250/25). The total microscope magnification for visual observation is computed by taking the product of the objective and eyepiece magnifications. For the objective and eyepiece just described, the total lateral magnification would be about 200x (10x eyepiece multiplied by the 20x objective).

Contributing Authors

Rudi Rottenfusser - Zeiss Microscopy Consultant, 46 Landfall, Falmouth, Massachusetts, 02540.

Stephen P. Price and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.