images . This is not just a rhetorical statement . In fact , this means that , some rich and subtle details of Jupiter ’ s atmosphere or a tiny new storm in Saturn can only be imaged , if one really works in technical basis as to use the limits of the imaging train ( meaning the telescope + eyepieces + filters + camera ). Sampling , or the sampling factor of the imaging train is another key factor for high-quality planetary images , that is , the relation between the image that is captured by the telescope and how it is reproduced in the sensor of the camera . It must be taken into account that we are capturing and reproducing a continuous image ( the planet ) in a non-continuous / digital media ( the pixels at sensor of the camera ). Extending the Nyquist theorem , regarding a punctual light ray and how many pixels will capture it in the sensor , we need at least a 3 x 1 sampling factor to avoid an imperfect reproduction of the image as well as the aliases , otherwise it will appear as sawtooth edges and somewhat imperfect and blurred details . Good planetary images must be taken with
an oversampling factor . It is worth mentioning that for Hi-Res planetary images it is common to use equivalent focal lengths of 8000 mm or above , meaning an ampliation above 1000 times , what makes sampling a real key issue . Hi-Res planetary imagers use specific techniques as the so-called “ lucky frames ”. As we know , one of the main restrictions for observing and specially for imaging , is the turbulence of the Earth ´ s atmosphere that strongly affects the image .
In short , lucky frames technique aims at acquiring a very large number of frames ( photos ) at high speed , thus a fraction of these tens of thousands of frames will be able to “ dribble ” this effect and will be afterwards selected among the better ones to be processed and to compose the final image . The good or poor stability conditions of the Earth ´ s atmosphere , known as seeing , is certainly above all , the main key factor to obtain an effective Hi-Res astronomic image . But , other factors , sometimes
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