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| en:ost:fokus [2016/11/10 22:45] – rhainich | en:ost:fokus [2016/11/10 23:12] (current) – [Aperture diaphragms] rhainich | ||
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| Aperture diaphragm proofed to be a very useful assistance in finding the best focus and in testing the quality of the telescope imaging-capabilities. Aperture diaphragm with two apertures are usually called Scheiner diaphragm, whereas aperture diaphragm with more than two apertures are denoted as Hartmann diaphragm. The aperture diaphragm are mounted before the Schmidt plate. | Aperture diaphragm proofed to be a very useful assistance in finding the best focus and in testing the quality of the telescope imaging-capabilities. Aperture diaphragm with two apertures are usually called Scheiner diaphragm, whereas aperture diaphragm with more than two apertures are denoted as Hartmann diaphragm. The aperture diaphragm are mounted before the Schmidt plate. | ||
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| For finding the focus, the telescope needs to be pointed to a bright light source (e.g. a bright star). Several images of the light source are recognizable in case the telescope is defocused, since the light rays from the different apertures of the diaphragm pass through different points of the focal plain. The distance between the different images of the light source can be reduced by adjusting the focus. The optimal focus has been reached when the different images are aligned. | For finding the focus, the telescope needs to be pointed to a bright light source (e.g. a bright star). Several images of the light source are recognizable in case the telescope is defocused, since the light rays from the different apertures of the diaphragm pass through different points of the focal plain. The distance between the different images of the light source can be reduced by adjusting the focus. The optimal focus has been reached when the different images are aligned. | ||
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| === Scheiner diaphragm === | === Scheiner diaphragm === | ||
| - | For our telescope, we have a Scheiner diaphragm with rectangular apertures, where the apertures are rotated by 45° towards each other (see the right figure). The advantage of this kind of Scheiner diaphragm is that the images of the object are superimposed with spikes, due to the diffraction at the apertures. According to the rotation of the apertures also the spikes of the different images are rotated by 45° towards each other. The spikes provide a good assistance in focusing the telescope, since the spikes form a symmetric " | + | For our telescope, we have a Scheiner diaphragm with rectangular apertures, where the apertures are rotated by 45° towards each other (see the right figure). The advantage of this kind of Scheiner diaphragm is that the images of the object are superimposed with spikes, due to the diffraction at the apertures. According to the rotation of the apertures also the spikes of the different images are rotated by 45° towards each other. The spikes provide a good assistance in focusing the telescope, since the spikes form a symmetric " |
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