Chapter 11 - IMAGE RECORDING

Abstract

Publisher Summary This chapter illustrates some characteristics of the recordings on photographic emulsions. To record an image, the photographic material is located within the evacuated electron microscope column. This situation provides nearly ideal recording conditions and is limited only by the characteristics of the photographic emulsion. It is also possible to record the image outside the column if it is transmitted by means of a fiber-optic system. This avoids the necessity of introducing the photographic film in the vacuum, but introduces, instead, a risk of losing resolution and fine detail. When the photographic plate or film is given an optimal exposure and has been properly developed, the emulsion density varies within a wide range. No large areas of either black or white are found unless the specimen contains uniformly electron-dense or electron-translucent regions. A loss in contrast will be evident in underexposed negatives and may lead to a loss of information. By increasing the exposure, the density of the negative increases, which results in an enhanced image contrast as well as a higher signal-to-noise ratio. However, when the negative is overexposed, the photographer loses much time making the prints. The dense negatives can be modified by different types of reducers. Some of these, such as Farmer's reducer, bleach the negatives with a retained degree of contrast; with other reducers, contrast may be gained or lost.