CELESTRON 11” (28 cm) SCT

We offer knobs for all versions of the Celestron 11” f/10 Schmidt-Cassegrain secondary with either standard or metric collimation screws, including Fastar, non-Fastar, and EdgeHD versions. Select knobs for your telescope from the list below.

Special Note: The Celestron 11” SCT uses either standard 6-32 or metric M3 collimation screws. Allen and set-style factory collimation screws have standard threads. For Phillips collimation screws, most silver screws are standard and most black screws are metric. See our hints for more information.
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A. Knobs for C11 f/10 with Flat Secondary Housing and Standard Collimation Screw Threads

Part: C11std
Fits: Celestron 11” (28 cm) f/10 SCT versions (metal or carbon fiber tube) with flat secondary housing and standard collimation screw threads (not for CPC 1100 or EdgeHD).

Knobs: Black plastic, 16 mm (5/8”) diameter
Threads: Black anodized aluminum alloy

Notes:
  1. Silver factory collimation screws usually have standard threads, but some silver Phillips screws have metric threads. Our hints will help you determine which screws are on your telescope. Make sure the knob threads match the factory screw threads before installing the knobs.
  2. The factory dust cover will fit normally with Bob’s Knobs installed.
  3. Celestron 11” SCTs manufactured prior to 2006 have standard collimation screw threads.

$19.95

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B. Knobs for C11 f/10 with Flat Secondary Housing (non-Fastar) and Metric Collimation Screw Threads

Part: C11metBO (black oxide steel); C11metSS (stainless steel)
Fits: Celestron 11” (28 cm) f/10 SCT versions with flat secondary housing and metric collimation screw threads (most CPC 1100).

Knobs: Black oxide steel (black) or stainless steel (silver), 12 mm (1/2”) diameter
Threads: Black oxide or stainless steel

Notes:
  1. Black Phillips factory collimation screws usually have metric threads, but some black Phillips screws have standard threads. Our hints will help you determine which screws are on your telescope. Make sure the knob threads match the factory screw threads before installing the knobs.
  2. Black oxide steel (shown in photo) is for dry environments. Lightly oil the knobs periodically as an anti-corrosion measure. Stainless steel provides better corrosion protection in coastal or high humidity areas, or in places where dew or other condensation is common.
  3. The factory dust cover will fit normally with Bob's Knobs installed.
  4. If your telescope has a factory-installed plastic cap over the collimation screws, it must be removed and set aside when Bob's Knobs are installed. The cover is cosmetic only and will not affect operation of the scope.

$20.95 (black oxide steel)
$25.95 (stainless steel)

Select Knob Type
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C. Knobs for C11 f/10 with “Trifid” Fastar Secondary Housing and Standard Collimation Screw Threads

Part: C11stdfst
Fits: Celestron 11” (28 cm) f/10 SCT versions (metal or carbon fiber tube) with standard thread factory collimation screws and "Trifid" rotary cover Fastar secondary housing. Factory collimation screws are silver Phillips. These knobs will also fit the C11 with Starizona Hyperstar if the collimation screws have standard threads.

Knobs: Black plastic, 16 mm (5/8”) diameter
Threads: Black anodized aluminum alloy

Notes:
  1. These telescopes can have factory collimation screws with either standard or metric threads. Silver Phillips collimation screws are standard thread. Some black Phillips collimation screws are also standard thread. See our hints for more information. If you discover your knobs have the wrong threads, you may return your knobs for exchange at no additional cost. Alternatively, you can order knobs with both standard and metric thread screws and return the unused set for a full refund.
  2. The factory dust cover will fit normally with Bob’s Knobs installed.
  3. 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.

$19.95

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D. Knobs for C11 f/10 with “Trifid” Fastar Secondary Housing and Metric Collimation Screw Threads

Part: C11metfst
Fits: Celestron 11” (28 cm) f/10 SCT versions (metal or carbon fiber tube) with metric thread factory collimation screws and "Trifid" rotary cover Fastar secondary housing. Factory collimation screws are black Phillips. These knobs will fit the C11 with EdgeHD optics. They will also fit the C11 with Starizona Hyperstar if the collimation screws have metric threads.

Knobs: Black plastic, 16 mm (5/8”) diameter
Threads: Stainless steel

Notes:
  1. These telescopes can have factory collimation screws with either standard or metric threads. Most models with black Phillips collimation screws have metric threads. There are a few black Phillips screws with standard threads. See our hints for more information. If you discover your knobs have the wrong threads, you may return your knobs for exchange at no additional cost. Alternatively, you can order knobs with both standard and metric thread screws and return the unused set for a full refund.
  2. 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.
  3. The factory dust cover will fit normally with Bob’s Knobs installed.
  4. 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.

$22.95