Master the Bullet Clutch & Focus
There's a bullet inside your telescope and how you master its use will determine the fate of your telescope!
(According to Celestron) The Celestron EdgeHD telescope series have a mirror with clutches to apply tension to a flexible rod attached to the primary mirror support. With enough tension from both clutches, they lessen mirror shift or mirror flop when the scope is moved around in different orientations while in use.
Because they are flexible, the mirror clutches won’t prevent focusing while tightened. However, because they do put force on the mirror, they should be loosened when focusing. Otherwise the combination of their force and the focusing effort may put unequal pressure on the primary mirror, causing it to bind or unevenly shift while focusing. Note: The EdgeHD 14”, like older Celestron 14” tubes, has two regular mirror locks in addition to the clutches. These locks do just that – lock the mirror. They should be used when the telescope is transported, not to prevent mirror shift. Never focus when these locks are engaged - you may damage either the focuser or mirror.
(According to link) The primary reason for focus shift in the SCT design is a result of the mirror continuing to settle when the final focus is approached using clockwise motion of the focuser. This is because the mirror can continue to settle due to the play between the threads of the focuser shaft and the carrier on the mirror. If you approach final focus using a clockwise, you are "pushing" the mirror down. When you stop, gravity will allow the mirror to now settle away from the treads that are pushing it down to the opposite face of the treads so that they are now "Holding the mirror up." The best results with a SCT will be to always approach final focus using counterclockwise turns of the focuser.
For imagers, this "Lifts" the mirror into final position so that play in the focuser is never allowed to occur. The mirror is raised into position so that the mirror carrier on the baffle is always left at the same orientation, an there is no play left for it to settle back from. For visual observers, the added benefit is that approaching focus using CCW turns will result in less chasing focus (inward direction for Refractors and Reflectors). If you overshoot final focus slightly, the eyes normal visual accommodation can easily adjust to refocus the image on their own. I have had the Celeston EdgeHD locks apart and I can assure you that the design, if the locks themselves, cannot cause any mirror shift. This means that the only shift is the same that comes with regular SCTs and the solution is an aftermarket external focuser, or using CCW motions of the focuser to approach final focus (to may not eliminate, but will greatly reduce shift). Link
