CELESTRON 8” (20 cm) SCT

We offer knobs for all versions of the Celestron 8” f/10 Schmidt-Cassegrain secondary with either standard or metric collimation screws, including Fastar, non-Fastar, and the classic orange tube. Select knobs for your telescope from the list below.

Special Note: The Celestron 8” 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 C8 f/10 Pre-1980 Orange-Tube Secondary

Part: C8org
Fits: Pre-1980 Celestron 8” (20 cm) f/10 SCT with orange optical tube and factory set-style collimation screws.

Knobs: Black plastic, 13 mm (1/2”) diameter
Threads: Black anodized aluminum alloy

Notes:
  1. These knobs will fit orange tube C8 models made prior to 1980. The secondary has factory set-style collimation screws with a fourth central screw in the secondary housing.
  2. Two sets of knobs, each with a different screw length, are included with your order. Use the length that fits your telescope best. There should be two or three screw thread turns above the secondary housing and the dust cover should fit without contacting the knobs.

$20.95

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B. Knobs for C8 f/10 Post-1980 Secondary with Standard Collimation Screw Threads

Part: C8std
Fits: Celestron 8” (20 cm) f/10 post-1980 SCT with factory Allen or silver Phillips collimation screws, with or without Fastar secondary with silver collimation screws (C8 black, or gray; Ultima 2000; NexStar 8; others). This includes the post-2000 orange-tube. Will not fit pre-1980 orange tube or most scopes with black Phillips factory collimation screws.

Knobs: Black plastic, 13 mm (1/2”) diameter
Threads: Black anodized aluminum alloy

Notes:
  1. These knobs will fit C8 models made prior to 2005 (except pre-1980 orange tube), and most post-2005 models with silver factory collimation screws.
  2. Most models with black Phillips factory collimation screws require C8 metric knobs (Item C below). However, a few post-2005 scopes have black Phillips collimation screws with standard threads. Here are some hints to help determine which screws your telescope has. Make sure the knob threads match the factory screw threads before installing the knobs. More information is in our Celestron technical paper.
  3. We provide spacers to raise the knobs slightly for easier use, but the spacers can be omitted if the knobs contact the inside of the full-aperture dust cover. Spacers are required for knobs installed on the Fastar secondary with silver collimation screws for proper clearance.
  4. Some telescope versions have a small plastic cover over the factory collimation screws. This cover 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.

$16.95

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C. Knobs for C8 f/10 Secondary with Metric Collimation Screw Threads (not for EdgeHD or Hyperstar)

Part: C8metBO (black oxide steel); C8metSS (stainless steel)
Fits: Most Celestron 8” (20 cm) f/10 SCT made in 2005 and later with black Phillips factory collimation screws that have metric threads. Includes SkyWatcher SCT and non-EdgeHD Fastar.

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

Notes:
  1. Most models with black Phillips factory collimation screws require metric knobs. A few post-2005 scopes have black Phillips collimation screws with standard threads. Here are some hints to help determine which screws your telescope has. Make sure the knob threads match the factory screw threads before installing the knobs. More information is in our Celestron technical paper.
  2. These knobs will fit the metric Fastar version only if it does not have EdgeHD optics. Scopes with EdgeHD optics require different knobs (Item D below).
  3. Black oxide steel (shown in photos) 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.
  4. The factory dust cover will fit normally with Bob's Knobs installed.
  5. Some telescope versions have a small plastic cover over the factory collimation screws. This cover 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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D. Knobs for C8 f/10 Secondary with EdgeHD Optics

Part: C8edgBO (black oxide steel); C8edgSS (stainless steel)
Fits: Celestron 8” (20 cm) f/10 SCT with Fastar secondary and EdgeHD optics.

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

Notes:
  1. These knobs will fit only the Celestron 8” SCT with Fastar secondary and EdgeHD optics. These telescopes are marked “EDGEHD OPTICS” on the corrector ring. Do not use these knobs on the non-EdgeHD Fastar secondary; the screws on these knobs are too long. Be sure to check that the thread length on our knobs matches the thread length on the factory collimation screws.
  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.

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

Select Knob Type
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E. Knobs for C8 f/10 Secondary with Hyperstar and Metric Collimation Screw Threads
s

Part: C8hypBO (black oxide steel); C8hypSS (stainless steel)
Fits: Celestron 8” (20 cm) f/10 SCT with metric collimation screws and Hyperstar option

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

Notes:
  1. These knobs are taller than our other metric knobs to compensate for the countersunk factory screws in the Hyperstar secondary.
  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.

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

Select Knob Type