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Sometimes this can be difficult to wrap your head around in Astronomy, as telescopes generally have a fixed aperture and focal distance, and simply use an eyepiece at the end to make a difference. If you, instead, look at a camera you can get the concept quite quickly. DSLR cameras have swappable lenses and many lenses include non-fixed focal distances ...


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The objective lens of a telescope forms an real image of the night sky, the size of that image is in proportion to the focal length of the objective lens. The reason for this is simple geometry: If two stars are 1 arcminute apart, and the lens is forming an image of them, then the further the image is from the lens, the further apart the images of the two ...


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The Raleigh criterion is the maximum theoretical limit that ignores the architecture, quality, and state of maintenance of optics. It basically says "assuming the optics in this instrument are PERFECT, this is the resolution you could get out of it". It's a calculation that looks only at the diameter and ignores everything else. In other words, no matter how ...


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The resolution of a telescope is the resolution of the image created by the primary mirror at the focal plane. It provides the minimum separation between two equal brightness stars that appear separate in that image. Often, astronomers put a photographic plate or a CCD at the focal plane, create long exposure photos and these can then be examined at ...



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