Bob's Knobs 3 Collimating knobs for Celestron 11" Edge HD with Trifid secondary


Availability: More on the way

These no-tool collimation knobs fit the Edge HD versions of the Celestron C11Schmidt-Cassegrain (those with a partially raised "Trifid" housing thatrotates to cover and uncover the metric black Phillips-head collimation screws) . . .
Our Product #: BKC11HD
Bob's Knobs Product #: C11METFST

Product Description

These knobs make it easy to collimate your EdgeHD version Celestron C11 for optimum image quality. You don't need any tools, so you never have to worry about losing a tiny Phillips-head 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 11" Celestron EdgeHD Schmidt-Cassegrain telescopes having black metric Phillips-head factory collimation screws and a "Trifid" Fastar secondary housing. The raised "Trifid" rotary secondary housing has a cover with three raised legs that rotate to cover and uncover the recessed collimation screws.  In addition to fitting the C11 with EdgeHD optics, they will also fit the C11 with the Starizona Hyperstar if the collimation screws have metric threads.

The Bob's Knobs collimating screws are made of stainless steel. Their knobs are black plastic, 10 mm (3/8") 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 one at a time 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.

Tech Details

Weight 1.6 oz.
Warranty 1 year


Review by:
Bobs Knobs make collimating a SCT a snap. They really are very convenient and helped me overcome my fear of wrecking something. Easy and clear instructions for installing (Posted on 10/7/2018)
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