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  Section: Biotechnology Methods » Tools and Techniques in Biological Studies
 
 
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Photography

 
     
 
Photomicrography
Photographically recording visual images observed through a light microscope is a useful means of obtaining a permanent record of activities. Using photomicrographs is the main means of recording electron microscope images.

Use of a camera on the microscope is straightforward. Merely center the object to be photographed, focus using the camera viewer, and depress the camera shutter button. Equipping the shutter with a shutter release cable will help prevent vibrations. This assumes that you have the proper exposure. Exposure and film type are the major problems of photomicrography. For most microscopes using a tungsten lamp source, there is very little light reaching the camera. Film that has a high enough exposure index (ASA speed) is too grainy to be used for effective work. In general, the faster the film, the less inherent resolution it will have. As in all things in photography, a compromise is called for.
 

The microscope projects an image of very low contrast, with low light intensity. A thick emulsion tends to lower the contrast even more. This results in photographs that are all gray, with no highlights (black and white). The tonal range is reduced significantly, using general film for photomicrography.

Use Kodak Technical Pan Film at an ASA of 100 for photomicrography. This is a thin-emulsion film with extremely high contrast. The contrast can even be controlled through the developing process and ranges from high (for photography of chromosomes), to moderate (used for general use), and low is not used in photomicrography. This same film can be used for copy work, since it reproduces images that are black and white.

Another means of increasing contrast is the use of colored filters within the microscope light path. Use a contrasting color to the object you wish to photograph. For example, chromosomes stained with aceto-orcein (dark red) can be contrast-enhanced by the use of a green filter. Human chromosome spreads stained with Giemsa (blue) can be enhanced by the use of a red filter. This trick is useful for routine viewing as well as photography.

 
The use of filters will increase the necessary exposure time. Technical Pan Film is also a relatively slow film. To establish the proper exposure, use the light meter built into the camera. If no light meter is available, you will have to shoot a roll of film and bracket several exposures to determine which is best. When using the built-in meter, remember that all light meters are designed to produce an image that is a medium gray. If you have a spot meter, be sure the spot is placed over an object that should be gray in the final image. If you have an averaging meter, be sure there is sufficient material in the viewfinder for a proper average exposure. If you do not know whether you have a spot or averaging meter, find out. This is not trivial. Suppose you wish to photograph a chromosome spread. The chromosomes are typically less than 1%–2% of the field of view. The meter will adjust the exposure so that the white field of light is exposed as gray, and your chromosomes will appear as darker gray on a gray field - in other words, extremely murky-looking. Performing karyotype analysis on this type of image is difficult or impossible.

For 35-mm cameras, be sure to rewind the film when all exposures have been completed.

Processing
After exposure of the film, it needs to be processed. Processing of black and white film has 3 steps. Develop the film, stop it from developing, and fix the emulsion so that it is no longer light-sensitive. Or, you can send your film out for processing.

Macrophotography
Macrophotography is used to record things that are too large to be viewed in the microscope. This is an excellent means of making permanent records of electrophoresis gels, bands observed during ultracentrifugation, and whatever else you wish to capture on film.

Two changes are required from the use of photography through a microscope. The camera must be removed from the microscope and equipped with a lens, and also, the type of film used must be changed.

 
     
 
 
     




     
 
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