| These knobs make it easy to collimate your Celestron C8 for optimum image quality. You don’t need any tools, so you never have to worry about losing a tiny Allen wrench or screwdriver in the grass in the dark. You adjust the collimation while looking through the eyepiece, so there’s instant feedback about how your optics are performing. Installation of the knobs is a snap with the included instructions, and you can undo the modification at any time. This knob set works with all 8" Celestron Schmidt-Cassegrain telescopes made in 2005 and later that use black Phillips-head collimating screws as shown in the feature image below. These include some CPC800 scopes. They do not work with Celestron scopes that use silver Allen head, Phillips head, or headless recessed set screw-style 6-32 collimation screws, whether with or without the Fastar compatible secondary system. Scopes using the silver collimating screws require the #BKC8 standard knob set. Check that the screw threads on the knob set you buy matches the factory collimating screw threads before installing. The collimating screws in this knob set are made of stainless steel. Their knobs are black plastic, 10 mm (3/8") in diameter. Some versions of the C8 have a small snap-in plastic cover over the factory collimation screws. This cover must be removed and set aside when these collimation knobs are installed. The cover is cosmetic only and will not affect the operation of the scope. The factory dust cover will fit on the scope with Bob's Knobs installed. The three collimation screws hold the secondary mirror and its mounting plate to the secondary housing. The mirror mounting plate pivots on a tang or spring at its center, and the collimation screws, which are threaded into the plate, adjust the mirror tilt (or collimation). Do not remove more than one of the original collimation screws at a time when installing Bob's Knobs, as the secondary mirror might fall off (if all three screws are removed at the same time), or the secondary can pivot inside the tube, scratching the corrector plate (if two screws are removed simultaneously). By removing only one factory collimation screw at a time, replacing it with a knob, and repeating this process for the other two collimation screws, there's no danger of dropping the secondary mirror. The instructions also recommend pointing the optical tube assembly slightly downward during the installation of the knobs for an added safety measure. Some scopes with the Fastar option have a fixed central knob mounted on the secondary housing for the user to hold while unscrewing the outer ring. The three collimation screws on this telescope thread into the secondary mirror mounting plate and hold it in place. As with the non-Fastar scopes with a central secondary screw, do not attempt to adjust this central Fastar knob.
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