GENERAL NEWTONIAN SECONDARY

Most mass-produced Newtonian telescopes from Celestron, GSO, Hardin Optical, Meade, Orion, Synta, and Zhumell use one of the secondary mirror configurations shown on this page. The photographs and descriptions below will help you determine which knobs to order.

A. Knobs for Set Screw Secondary

Part: CNsec30 or CNsec35
Fits: Celestron C8-N/NGT, C10-N/NGT, Orion Astrograph, Astroview, SkyQuest XX and XT, Skyview, SkyWatcher, StarBlast, GSO, and many others.

Secondary Characteristics: 4-vane spider, a deeply recessed center screw, and factory headless set (grub) collimation screws. The secondary plate holding the screws is about 20 mm (3/4”) thick. This is a very common Newtonian secondary configuration.

Knobs: Black plastic, 13 mm (1/2”) diameter
Threads: Stainless steel

Notes:
  1. We offer knobs with screws having either 30 mm or 35 mm length. Order knobs with a screw length sufficient to allow the knobs to clear the secondary housing. Knobs with 30 mm screws are the most common in this configuration.

$20.95

Screw length
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B. Knobs for 4-Vane Phillips Screw Secondary

Part: CNsec25 or CNsec35
Fits: Celestron Starhopper, Meade Lightbridge, many GSO, Hardin Optical, and Zhumell models

Secondary Characteristics: 4-vane spider, a deeply recessed center screw, and factory Phillips collimation screws. The secondary plate holding the screws is about 20 mm (3/4”) thick.

Knobs: Black plastic, 13 mm (1/2”) diameter
Threads: Stainless steel

Notes:
  1. The factory collimation screw length, measured below the head, can be either 25 mm or 32-35 mm. Order knobs with the correct screw length for your application. Knobs with 35 mm screws are the most common.

$20.95

Screw length
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C. Knobs for 3-Vane Phillips Screw Secondary

Part: CNsec25
Fits: Early Orion SkyQuest XT series and a few others

Secondary Characteristics: 3-vane spider, a shallow recessed center screw, and factory Phillips collimation screws. The secondary plate holding the screws is about 6 mm (1/4”) thick.

Knobs: Black plastic, 13 mm (1/2”) diameter
Threads: Stainless steel

$20.95