GS-350 PAPO Apochromatic Guide Scope (AC / AR)
350mm focal length | 58mm aperture | f/6
The GS-350 is the longest focal length model in the GS range, engineered for high-precision guiding on medium to long focal length imaging systems. With a 350mm focal length and 58mm aperture, it delivers increased guiding resolution while maintaining excellent star correction across the field.
Overview
The GS-350 features a proprietary three-element PAPO (Planar Apochromatic with integrated field flattener) optical design incorporating ED glass. This configuration reduces chromatic aberration, corrects field curvature and preserves accurate star colour — producing tight, well-defined guide stars for reliable mount corrections.
Broadband multi-layer anti-reflection coatings maximise light transmission, while precision-machined internal anti-reflection threading suppresses stray light and enhances contrast. The result is stronger guide star signals and more consistent guiding performance during long exposures.
The corrected 1-inch image circle supports guide cameras up to 1" sensor size and can accommodate larger sensors for experimental wide-field imaging applications.
Optical Performance
PAPO Apochromatic Optical System
The ED triplet and integrated field correction deliver sharp, well-controlled star profiles across the usable field. The 350mm focal length provides improved guiding precision compared to shorter guide scopes, making it ideal for imaging systems in the 800–1200mm focal length range.
GS-350 Spot Diagram
High Transmission Coatings & Internal Baffling
Multi-layer AR coatings and internal light control reduce glare and improve contrast, ensuring consistent guide star detection even in light-polluted environments.
Mechanical Design
CNC-Machined Aluminium Construction
The GS-350 optical tube, rings and dovetail are precision CNC-machined for rigidity and durability. Despite its longer focal length, the OTA weight remains well balanced for stable mounting on equatorial systems.
Modular Optical Tube Design
An integrated M48 extension tube allows flexible back-focus configuration for visual use, guiding or imaging setups.
AC vs AR – Focuser Options
- AC Version: Rackless (Crayford-style) focuser designed for smooth manual focusing with lightweight guide cameras.
- AR Version: Rack-and-pinion focuser with higher load capacity, compatible with ToupTek AAF electronic focusers and heavier cooled cameras.
Choose AC for lightweight guide camera setups.
Choose AR if using heavier cameras or planning motorised focusing.
Compatibility
- 350mm focal length (f/6)
- 58mm aperture
- Supports guide and planetary cameras up to 1" sensor size
- 1.25" eyepiece interface + external M42×0.75 thread
- Multiple M5 accessory mounting points
- Dovetail base compatible with tripods & equatorial mounts
- OTA weight: 1.21kg
What's in the Box
FAQ
What imaging systems is the GS-350 best suited for?
The GS-350 is ideal for guiding imaging telescopes between approximately 800mm and 1200mm focal length, where increased guiding resolution is beneficial.
Can this be used for visual observing?
Yes. The 1.25" interface allows use with standard eyepieces for wide-field viewing or star-hopping applications.
