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The collimation of an SCT can be a daunting task for a beginner, but it is an absolutely necessary process to get the most out of your telescope! Doing the collimation with the factory Phillips screws is certainly doable, but requires a lot of back and forth between the eyepiece and the secondary mirror. You also need to work, in the dark, close to the corrector plate with a sharp metal screwdriver, requiring a lot of concentration and precision in your movements.

By replacing the factory Phillips collimation screws of your Celestron 11" with a set of Bob's Knobs collimation thumbscrew, you can make the process of collimation an effortless and risk-free task. Simply grab a Bob's Knobs thumbscrew and turn!

Fits: Celestron 11" (28 cm) f/10 SCT versions (metal or carbon fiber tube) with metric thread factory collimation screws and Fastar secondary housing. This housing can have either a "Trifid" rotary cover or a simple knob in the center and no rotary cover. Factory collimation screws are black Phillips. These knobs will fit the C11 with EdgeHD optics. They will also fit the C11 with Starizona Hyperstar only if the collimation screws have metric threads.

Collimation screws on these telescopes are small with very fine threads. Knobs must be tightened gently (just enough to hold the secondary in place) to prevent damage to either the knob or secondary assembly.

Knobs include a set of long spacers so they sit slightly above the rotary cover opening.

The factory dust cover will fit normally with Bob’s Knobs installed.

The rotary secondary cover must remain open when the knobs are installed. The cover is cosmetic only and will not affect operation of the telescope.

Knobs: Black plastic 16 mm (5/8") diameter

Threads: Available in stainless steel.

*Black oxide steel is only adequate for dry environments. David Astro only offers stainless steel Bob's Knobs thumbscrews, as they are more suitable for Canadian weather. Stainless steel provides better corrosion protection in locations where dew is common.