| These knobs make it easy to collimate your Celestron C8 with EdgeHD optics for optimum image quality. Please note that these knobs will fit only the Celestron 8" SCT with a Fastar secondary mirror holder and EdgeHD optics. These telescopes are marked “EDGEHD OPTICS" on the outer retaining ring that holds the corrector plate in place. Do not use these knobs on a non-EdgeHD Fastar secondary, as the screws on these knobs are too long for non-EdgeHD scopes. Be sure to check that the thread length on collimating knobs matches the thread length on the factory collimation screws before installing the knobs.
You don’t need any tools to collimate your scope, 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.
The collimating screws in this knob set are made of black oxide steel. Their knobs are black oxide steel, 12mm (1/2") in diameter.
The factory dust cover will fit normally 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.
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