Photomicrography Exposure (With ISO) Calculation

Use a known film exposure time measured from brackets under standardized conditions of ISO, magnification, and numerical aperture to determine exposure for a new objective of different magnification and numerical aperture with film having a different ISO value using this interactive Flash tutorial. Instructions for operation of the tutorial appear below the program window.

Film exposure varies directly as the square of the magnification and inversely as the square of the numerical aperture. If the optimal exposure time for a particular set of conditions is termed the Standard Time, then a new exposure time can be calculated with the tutorial above.

To operate the tutorial, select a measured exposure time between 0.05 seconds and 8 minutes using the Standard Time arrow buttons. Next, select the correct objective magnification and numerical aperture that produced the measured exposure time using the Standard Magnification and Standard Numerical Aperture menus. Also select the ISO of the film used to measure exposure times using the Old ISO pull-down menu. After selecting the standard conditions, use the New Numerical Aperture, New Magnification, and New ISO menus to select these new values. When the new values are input, the Calculated Exposure Time boxes will automatically present the calculated exposure time.

Contributing Authors

Mortimer Abramowitz - Olympus America, Inc., Two Corporate Center Drive., Melville, New York, 11747.

Brian O. Flynn and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.