Remove the screws and the retaining ring. Before actually removing the corrector plate, check around the edge of the corrector for an engraved serial number. Use a pencil or other form of marking device to mark the location of this serial number on the backing ring against which the corrector plate rests. Serial number aside, the “ribbed” rear cell indicated this wasn’t no spring chicken. Another tip-off to the C8’s vintage was the weird stuff on the top of the tube. There was a camera piggyback bracket on the rear cell and a corresponding aluminum block on the corrector assembly. Celestron offered what was basically the C8/5 tripod and wedge for that purpose, and that did indeed make for a very stable platform for Little Kitty. Unfortunately, adding those items jacked the already surprisingly high price up to a cool seven-hundred and ninety-five simoleons, equivalent to at least two-thousand 2010 dollars, depending on. Fully computerized 8 Celestron GoTo telescope with NexStar hand controller containing a 40,000-object database Big 203mm (8.0) Schmidt-Cassegrain optics with 2032mm focal length (f/10) StarBright XLT high-performance optical coatings for enhanced image brightness Computerized CG-5 equatorial mount has dual DC servo motors, autoguider and auxilliary ports Includes 25mm (81x) eyepiece, 6x30.

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. Please use care to select the correct knobs for your telescope. Each knob set is different and they are not interchangeable. Price is for a complete set of knobs.

Special Note: The Celestron 8” SCT uses either standard 6-32 or metric M3 collimation screws. Allen, silver Phillips, and set-style factory collimation screws have standard threads. Most black Phillips screws are metric. See our hints and our Celestron technical paper.for more information. If you order knobs with the wrong screws, contact us using the link at the bottom of this page for return instructions.
_______________________________

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. These screws can be either Allen or slotted.
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.
3. Do not adjust the center screw; this is the secondary pivot screw.

$20.95
_______________________________

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 withoutFastar secondary with silver collimation screws (C8 black, or gray; Ultima 2000; NexStar 8; many others). This includes the post-2005 orange-tube. Will NOT fitpre-1980 orange tubeor 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; see Item A above), 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.
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
_______________________________

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. Will NOT fit Celestron telescopes made before 2005.
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.
2. Some C8 scopes have metric collimation screws that are 10mm long rather than the more common 8mm, and you should install knobs without the white spacers.
3. These knobs will fit themetric Fastar versiononly if it does NOT have EdgeHD optics. Scopes with EdgeHD optics require different knobs (Item D below).
4. Black oxide steel (shown in photos) is for dry environments. Lightly oil the knob top and knob serrations 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.
5. The factory dust cover will fit normally with Bob's Knobs installed.
6. 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)
_______________________________
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 knob top and knob serrations 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)
_______________________________

E. Knobs for C8 f/10 Secondary with Hyperstar Conversion Kit and Metric Collimation Screw Threads

Part:C8hypBO (black oxide steel); C8hypSS (stainless steel)
Fits:Celestron 8” (20 cm) f/10 SCT with metric collimation screws and the conversion kit for the Hyperstar option
Knobs: Black oxide steel (black) or stainless steel (silver), 12 mm (1/2”) diameter
Threads: Black oxide or stainless steel
Notes:

Old Celestron Manuals

1. These knobs are taller than our other metric knobs to compensate for the countersunk factory screws in the Hyperstar secondary conversion kit.
2. Black oxide steel (shown in photo) is for dry environments. Lightly oil the knob top and knob serrations 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.

Celestron C8 Serial Numbers

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

Celestron Starsense Manual