Tα άρθρα που παρατέθηκαν είναι πάρα πολύ ενδιαφέροντα και αμέσως δημιουργούν ερωτήματα. πχ από το άρθρο του fred Ley: All eyepieces have a critical focal ratio. If the scope is faster than the critical number, the eyepiece fails to perform (1). The critical F ratio for both Abbes and Brandons is F7. This includes all Maksutov and SCT type instruments, but not fast refractors or reflectors. This point cannot be overestimated. If you pair a Brandon (or Abbe) with a long focal length instrument, the result is everything the scope is capable of. If your scope is fast, look for one of the new designs that actually contain an integral Barlow. Unfortunately, there are no classical orthoscopics that work well with fast scopes, but some designs approach these in performance (2). At F6.9, Chris Lord said, �efinition was noticeably superior in the Brandon� But this was not the case with a Newtonian at F4.7. Whether this is because F4.7 is too fast, or because some eyepieces �ccidentally� compensate for the coma of a fast reflector, I do not know (1) Υπάρχει τέτοιο πράγμα στα προσοφθάλμια όπως το βέλτιστο F στο οποίο αποδίδει τα μέγιστα ένα προσοφθάλμιο? Γνωρίζω για κάποια που δεν αποδίδουν καλά σε γρήγορα F αλλά για κάτι τέτοιο πρώτη φορά ακούω (2) οι ορθοσκοπικοί δουλεύουν καλά με γρήγορα τηλεσκόπια? πχ F5 Κοιτάξτε μετά τι λέει ο τύπος: In passing, I remark about the Questar legend. In recent years, this has been pooh-poohed, as in �here are no magic telescopes. While there is no magic, let us examine whether there is any reason why a Questar could outperform a �erfect apo.�It is commonly believed in amateur circles that the central obstruction of the Questar means that an apo will best it. Would you believe me if I tell you that exactly the opposite is the case? The knowledge comes from the author of the website, www.telescope-optics.net, where it is stated, �FONT COLOR="#000000">Obstructed aperture has significantly better contrast transfer - even from that of a perfect aperture - in the right half of MTF frequency range (i.e. for details smaller than 2λF linear, or 2λ/D in radians. Even in the left half of the graph (range of resolvable low contrast details), obstructed aperture has an edge.�/FONT>