GS Series Guide Scopes GS-250AC, AR | GS-350AC, AR

Specifications

• 

  PAPO Apochromat
  (Planar APO)
• 

  Multi-layer Coatings
  Broadband AR
• 

  1.25-inch /
  31.7 mm Port
• 

  Rear M42
  External Thread
• 

  Focal Length 250 mm (250)
  350 mm (350)
• 

  Aperture 50 mm (250)
  58 mm (350)
• 

  f/5 (250)
  f/6 (350)
• 

  Wide Compatibility
  Versatile Setups

PAPO Apochromatic Optical Design
True Star-Color Reproduction

The GS Series guide scopes feature a proprietary three-element PAPO (planar apochromat with integrated field flattener) configuration with one ED element, effectively correcting chromatic aberration, astigmatism, and field curvature. Designed around a flat, well-corrected 1-inch image circle, they deliver crisp, pinpoint star images for accurate guiding, while also supporting visual use and entry-level night-sky/DSO imaging.

GS-250 Spot Diagram

GS-350 Spot Diagram

High-Transmission Coatings + Anti-Reflection Threads
Boost Guiding Sensitivity

All optical surfaces use broadband multi-layer AR coatings to minimize reflections and maximize transmission. The internal barrel is precision-machined with anti-reflection threads and additional stray-light suppression, greatly improving image contrast.

CNC Precision Machining
Fine Matte Finish

The tube, rings, and dovetail plate are CNC-machined from aluminum alloy for a balance of low weight and structural strength. Anodized surfaces provide wear and corrosion resistance suited to field astronomy. The fine matte texture is comfortable, durable, and non-slip.

Modular Structure
for Maximum Flexibility

A proprietary universal M48 extension tube with anti-reflection treatment forms the main barrel, allowing flexible combinations to match optical path requirements—from visual observing to astrophotography.

GS-250 Guide Scope + GPM Guide Camera

GS-350 Guide Scope + Diagonal + Eyepiece

GS-350 Guide Scope + Filter Drawer (optional E-focuser) + DSO Camera

* Due to focal length limits, GS-250 may not reach focus with a diagonal.

Dual Focusing Options
Choose What Suits You

• Rackless Focuser (AC versions): FSB-125C rackless focuser with precision bearing guides and a classic Crayford-style mechanism for smooth focusing and stable optical alignment—ideal for light-load manual imaging.
  

• Rack-and-Pinion Focuser (AR versions): FSB-125R gear-driven focuser with precision bearing guides for higher focusing accuracy; compatible with ToupTek Astro AAF electronic focuser, suitable for autofocus and heavier payloads.

  

Wide Compatibility · Rich Configurations
Seamless System Integration

Built for flexibility: support for 1-inch sensors, direct threaded connections, and multiple mounting points let the GS Series integrate smoothly with a wide range of cameras and setups.

• 1) Supports high-quality imaging with guide and planetary cameras up to 1-inch sensor size.

  

• 2) Focuser end: 1.25-inch inner diameter with external M42×0.75 thread for direct connection to mainstream cooled cameras.

  * Recommended sensor size ≤ 1 inch.
  

• 3) Multiple M5 threaded holes on the top and sides of the tube rings for attaching additional astronomy accessories.

  

• 4) Dovetail plate bottom with multiple M6 threaded holes plus one 3/8-16 thread for quick mounting to tripods or equatorial mounts.

  

• 5) Universal M48 extension tube assembly for the main barrel; swap in a short tube when using an eyepiece or diagonal.

  

All-New Upgrades

Compared with the previous FS series, the new GS series is upgraded from optical design to overall performance.

Dimensions

GS-250AC Dimensional Drawing

GS-250AR Dimensional Drawing

GS-350AC Dimensional Drawing

GS-350AR Dimensional Drawing

What's in the Box

The GS series brings comprehensive upgrades over the FS series—from optics to performance.

• Guide Scope Box
• GS-250AC/AR or GS-350AC/AR Guide Scope
  (with tube rings / dovetail & focuser)
• Dust Cap