| These knobs make it easy to collimate your Celestron C11 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. While it may be a long reach for some people, you can usually adjust the collimation by yourself 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 late model aluminum optical tube 11" Celestron Schmidt-Cassegrain telescopes and most carbon fiber optical tube versions. These scopes have a raised “Trifid" rotary secondary housing that has a cover with three raised legs that rotate to cover and uncover the recessed set screw-style collimation screws. These screws are too long for a C11 optical tube with a flat secondary housing, no matter what tube material it is made from. Most 11" aluminum optical tube scopes, and a few of the carbon fiber tube scopes, have a flat non-rotating cover secondary housing that requires the #BKC11M knobs designed for the metal tube versions of the scope. If you have this type of flat secondary housing, do not buy this knob set. The Bob’s Knobs collimating screws themselves are made of black anodized aluminum alloy. Their knobs are black plastic, 16 mm (5/8") in diameter. The factory dust cover will fit on the scope normally with Bob's Knobs installed. The rotary “Trifid" secondary cover must remain open when Bob’s Knobs are installed in place of the recessed set screw-type collimation screws. The cover is cosmetic only and will not affect the operation of the telescope. 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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