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Question - dealing with spherical ab in a cassegrain
Simply put, does moving the eypiece position forward into the light cone
(toward the secondary) of a cassgrain system, have any effect in curing or minimising spherical aberration in cassegrain systems; the CAA 24" CAA Boller Chivens is the case in question. This is the remedy Director of the CAA B&C, John Centala, has settled on. John and his colleagues John Leeson and Greg Frohner say this method was found in some mathematical treatise on cassegrain systems? (The exact reference remains 'undisclosed'.). Would moving the eyepiece forward into the light cone not be tantamount to masking the outer edge of the primary? How would one determine which element in the system is causing the 'supposed' spherical aberration? (Note* After the telescope was assembled by those above I pointed out that star tests clearly indicated the secondary was being pinched. A year later, the secondary retainers were adjusted and stress relieved which resulted in improved images but the new claim of severe spherical aberration.) Any comments appreciated. .. |
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Question - dealing with spherical ab in a cassegrain
On 2011-07-03, jwarner1 wrote:
Simply put, does moving the eypiece position forward into the light cone (toward the secondary) of a cassgrain system, have any effect in curing or minimising spherical aberration in cassegrain systems; the CAA 24" CAA Boller Chivens is the case in question. This is the remedy Director of the CAA B&C, John Centala, has settled on. John and his colleagues John Leeson and Greg Frohner say this method was found in some mathematical treatise on cassegrain systems? (The exact reference remains 'undisclosed'.). Would moving the eyepiece forward into the light cone not be tantamount to masking the outer edge of the primary? How would one determine which element in the system is causing the 'supposed' spherical aberration? (Note* After the telescope was assembled by those above I pointed out that star tests clearly indicated the secondary was being pinched. A year later, the secondary retainers were adjusted and stress relieved which resulted in improved images but the new claim of severe spherical aberration.) Any comments appreciated. The focal plane of the telescope and the focal plane of the eyepiece must coincide for the telescope to be in focus - no ifs ands or buts. You can't move the eyepiece "up into the light cone". The spacing between the secondary and the primary on a classical cassegrainian telescope has to be within a very tight range of only a few millimeters to avoid spherical abberation. If fiddling with the secondary mount changed the spacing between the hyperbolic secondary mirror and the parabolic primary mirror too much the result would be spherical aberration. Bud |
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Question - dealing with spherical ab in a cassegrain
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