| 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 prior to 2005 that use factory Allen, silver Phillips, or headless set-style 6-32 collimation screws, with or without Fastar compatible secondary as shown below (C8 orange, black, or gray; Ultima 2000; NexStar 8). and all 2005 and later models except those that use black Phillips-head collimating screws as shown below. Almost all black Phillips screw models require C8 metric knob set #BKC8M. 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 black anodized aluminum alloy. Their knobs are black plastic, 13mm (1/2") 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.
Spacers are included for use with the knobs installed on the Fastar compatible secondary to raise the knobs slightly for easier use. These spacers can be optionally used on other models with Allen or Phillips factory collimation screws to raise the knobs for easier access, but check that the full-aperture dust cover fits without contacting the knobs. The spacers should not be used on telescopes with set-style factory collimation screws.
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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