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Interactive Tutorials

Exposure and Color Balance in Photomicrography

Photography through the microscope is complicated by a wide spectrum of unexpected color shifts and changes that affect how the image is rendered on the film emulsion or digital electronic image capturing device. These unexpected imaging results are caused by a number of factors ranging from incorrect color balance between the light source and the film emulsion to optical artifacts such as aberration and lamp voltage fluctuations. This tutorial explores how exposure and color balance affect the qualities of color photographs using both everyday subjects and photomicrographs captured in the microscope.

Upon initialization, two radio buttons labeled Photomicrographs and Photographs appear in the center portion of the tutorial window. These buttons enable the visitor to toggle between a set of images taken through the microscope and a set of stock photographs. After choosing a photograph set, use the pull-down menu to select a single image for manipulation, which will then appear in the tutorial image window. In order to adjust the effective exposure of the image, first choose an exposure increment (plus or minus 1/3, 1/2, or one f-stop) by clicking on the appropriate radio button, and then use the slider to darken or lighten the image. As the slider is moved to the left, the image will successively darken in the increments dictated by the exposure increment selection. Moving the slider to the right will progressively lighten the image by the same amounts. To apply color compensating filters, choose the appropriate filter from the left-hand menu (Red, Blue, Green, Cyan, Magenta, and Yellow), and click the check boxes on the right-hand side of the applet to apply a density to that particular filter. The lower check boxes, labeled Add, allow application of two or more filters simultaneously.

After the basis of a color photomicrography problem has been determined, it is usually very easy to correct with the appropriate use of filters of one type or another. Filters are used to selectively block or decrease the intensity of selected wavelengths while transmitting all other portions. A variety of filters are commercially available to assist the photomicrographer in compensating for optical and illumination problems in order to obtain the highest quality images possible. Many photomicrography color shifts or casts can be cured by inserting the appropriate Kodak Wratten Color Compensating filter into the optical pathway. Other filters such as neutral density, contrast enhancement, ultraviolet absorption, heat absorption, infrared, and filters designed to assist in bringing out details of biological stains are also commonly used.

Contributing Authors

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

Matthew J. Parry-Hill, Ian D. Johnson, and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.



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