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Explore Scientific 3-inch Self-Centering Focuser

Original price $849.99 - Original price $999.99
Original price
$849.99 - $999.99
Current price $849.99
In stock
In stock
In stock

Ships To: United States & Canada 🇺🇸 🇨🇦

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Estimated Delivery Time: 3-7 Business Days

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We offer free U.S. shipping to the lower 48 States - on most orders over $150 USD. Some limitations apply.

Shipping fees will apply on most orders shipping across Canada, with some exceptions.

We offer a 30 Day Return Policy on most of the products that we carry.

For full details on our Shipping & Returns Policy, please click here.


The vast majority of products that we sell, with a few exceptions, are covered under Warranty.

To view the Warranty details for each brand that we sell, including products that do not qualify for Warranty, please visit here.

Explore Scientific 3" Self-Centering Focuser - available for 152mm, 165mm, & ED127 Refractors (both CF and White Tube models)

With its ability to support heavy imaging trains without sacrificing stability, precision or smooth rotation, the robust Explore Scientific 3-inch Self-Centering Focuser is designed to meet the demanding requirements of astrophotography.

This heavy-duty focuser has a self-centering compression system that applies pressure equally to the draw tube, guaranteeing a tight, secure fit. This uniform pressure creates a stable base for an imaging setup and prevents flex, tilt and image shift. The draw tube, which is long enough to eliminate the need for extension tubes, is moved by a helical rack-and-pinion system lubricated with marine-grade PTFE silicone for an easy glide with maximum precision and minimal backlash. The interior of the draw tube has a diameter of 3 inches that is lined with multiple baffles to reduce reflection.

The draw tube, which has a travel of 84.5mm, is supported by a locking clutch system. The focusing system has a lifting capacity of 17 pounds. Moderate tightening offers an infinite range of tension to best suit the application.

Weighing in at 5.7 pounds, the focuser is made of black anodized aluminum. It has a 9:1 focus system with stainless-steel ball bearings and stainless-steel focus shaft. This system works as a clutch to prevent damage to the focusing mechanism. The focusing system is compatible with popular after-market electric focuser devices.

A back cell adapter with no-tool knobs attaches the focuser at four contact points to select Explore Scientific refractors with apertures ranging from 120mm to 140mm. The knobs on the adapter can be hand turned, eliminating the need for a hex key. This makes it easy to adjust the rotation of the focuser with minimal observing or imaging interruption. A Teflon ring on the focuser adds to the smooth rotation. 

For versatility, the focuser can hold 2-inch or 3-inch visual or camera accessories and comes standard with twist-lock. In addition to allowing accessories to be secured with a compression fitting, this draw tube’s M82 x 1.25 pitch thread accepts adapters with a variety of uses.

NOTE: The Explore Scientific 152mm and 165mm models do not require this back cell adapter. The 3-inch Self-Centering Focuser fits perfectly into the back cells on these telescopes.

NOTE: Explore Scientific white-tube telescopes with threaded back cells MUST BE shipped to Explore Scientific for installation of the back cell adapter. This will be arranged by customer service.


  • Item Number ES-FOC3 
  • Lifting Capacity - 17 lbs/37.4 kg 
  • Draw Tube Thread - M82 x 1.25 
  • Draw Tube Travel - 84.5 mm/3.32 inches 
  • Draw Tube Clear Interior Diameter - 76.2 mm/3 inches 
  • Draw Tube Baffles - 14 
  • Focus System - Helical rack & pinion 
  • Reduction Ratio - 9:1 with stainless steel ball bearings and shaft 
  • Attachment mechanisms - Self-centering compression 
  • Weight of focuser - 5.7 pounds including the 3-inch to 2-inch twist-lock adapter 
  • Compatible with electric focusers - Yes 
  • Compatible with 3-inch 2-inch and 1.25-inch eyepieces - Yes 
  • Telescope compatibility - Explore Scientific Refractor Telescopes 120mm and larger; custom back cells available on request for other brands of Refractor Telescopes 120mm and larger

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