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If you want to or have to document microscope images, the easiest way is to hold a standard camera to an eyepiece and to release the exposure. This will actually work, since the design of the camera is identical to that of the eye. The objective is the lens, and the film plane the retina. However, photos taken in this way will exhibit poor quality (see accompanying illustration) because the optical alignment is not correct. In particular, the pupil of the camera lens is not illuminated, which results in unsharp images.
The lateral magnification is much too small, i.e. the frame is not filled by the image; furthermore, the lens stop can also be a hindrance in the light path, not to mention the correct exposure.
Therefore, the camera on the microscope has its own camera port. The accompanying illustration shows the typical binocular photo/TV tube. In addition to the normal eyepieces, the tube contains a switchable beam splitter – a prism in most cases – which allows the entire light, or parts of it, from the tube lens to travel straight to the top to the camera/TV adapter. Here, the familiar intermediate image is formed.
The beam path for photomicrography in the accompanying illustration shows the path of the light from the tube lens up to the film plane. The intermediate image (2) formed by the tube lens (1) and lenses of the photo eyepiece (3) is magnified by the photo eyepiece (3). For the camera lens (5), the light rays then look again as if they have come from far away. If the central shutter (4) is opened for exposure, the objective produces a further – now much larger – intermediate image (6) in the film plane.
The new intermediate image produced by the photo eyepiece is now adapted to the film size. It is additionally magnified for 35 mm films with an overall factor of 2.5x. While the original intermediate image had a diameter of 20 mm, the diameter in the film plane now is 20 mm x 2.5 = 50 mm. The image diagonal in 35 mm films (36 mm x 24 mm edge length) is approx. 43 mm, which is less than 50 mm.
The photomicrography equipment in the accompanying illustration consists of a special camera connector with a photo eyepiece. This basic design is used with all camera equipment. As regards the choice of the camera, the following options exist:
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