GS-300 PAPO Apochromatic Guide Scope (AC / AR)
300mm focal length | 50mm aperture | f/6
The GS-300 is engineered for astrophotographers who require increased guiding precision for medium to long focal length imaging systems. With its 300mm focal length and PAPO ED triplet optical design, it delivers sharp, well-corrected guide stars across the field for accurate and stable mount corrections.
Key Benefits: Increased Guiding Resolution • Flat-Field Correction • Mechanical Stability
Overview
The GS-300 features a proprietary three-element PAPO (Planar Apochromatic with integrated field flattener) optical system incorporating ED glass. This configuration reduces chromatic aberration and corrects field curvature, producing tight and consistent star profiles across the usable image circle.
Broadband multi-layer anti-reflection coatings maximise light transmission, while precision-machined internal anti-reflection threading suppresses stray light and improve contrast — resulting in stronger guide star signals and more consistent tracking performance.
The corrected 1-inch image circle supports guide cameras up to 1" sensor size and also allows limited wide-field imaging or visual use.
Optical Performance
The 300mm focal length provides greater guiding precision than shorter guide scopes while maintaining a usable field of view. It is especially well suited to imaging telescopes in the 700–1000mm focal length range, where improved guiding resolution enhances long-exposure stability.
Mechanical Design
The optical tube, rings and dovetail are CNC-machined from aluminium for rigidity and durability. Despite its longer focal length, the GS-300 remains well balanced with an OTA weight of approximately 0.94kg, making it stable without overloading mid-sized equatorial mounts.
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 offering increased load capacity and compatibility with motor focusers such as the ToupTek AAF.
Choose AC for lightweight guide setups.
Choose AR for heavier cameras or motorised focusing upgrades.
Specifications
- 300mm focal length (f/6)
- 50mm aperture
- PAPO ED triplet with integrated flat-field correction
- Rear thread: M42×0.75 (T2 standard)
- 1.25" eyepiece interface
- Supports guide cameras up to 1" sensor size
- Multiple M5 accessory mounting points
- Dovetail base compatible with equatorial mounts
- OTA weight: 0.94kg
Ideal Use Case
The GS-300 offers a refined balance between resolution and portability, making it an excellent choice for guiding imaging systems between 700mm and 1000mm focal length where increased precision is beneficial.
Optically refined and mechanically robust, the GS-300 is built for astrophotographers who expect reliable, repeatable guiding performance.
