GS-250 PAPO Apochromatic Guide Scope (AC / AR)
250mm focal length | 50mm aperture | f/5

The GS-250 is a precision 250mm flat-field guide scope engineered for serious astrophotography. With its balanced focal length and ED triplet optical design, it delivers sharp, well-corrected guide stars for accurate and stable deep-sky imaging.

Key Benefits: PAPO Precision • Stable Guiding • High Contrast Star Profiles

Overview

The GS-250 features a proprietary three-element PAPO (Planar Apochromatic with integrated field flattener) optical system incorporating ED glass. This configuration reduces chromatic aberration, corrects field curvature and preserves accurate star colour — resulting in tight star profiles across the field.

Precision-machined internal anti-reflection threading and broadband multi-layer AR coatings enhance light transmission and suppress stray light. The result is improved contrast and more reliable guide star detection for consistent mount corrections.

Designed around a flat, corrected 1-inch image circle, the GS-250 supports guide cameras up to 1" sensor size and can also be used for wide-field imaging or visual applications.

Optical Performance

PAPO Apochromatic Triplet System

The ED triplet with integrated field correction delivers sharp, pinpoint stars with minimal chromatic aberration. The 250mm focal length offers an ideal balance between wide field and guiding precision, making it especially well suited to imaging telescopes in the 500–900mm focal length range.

GS-250 Spot Diagram

High Transmission Coatings & Internal Light Control

Multi-layer broadband AR coatings increase light throughput, while internal baffling reduces glare and improves contrast — ensuring strong guide star signals even under less-than-ideal sky conditions.

Mechanical Design

CNC-Machined Aluminium Construction

The optical tube, rings and dovetail are precision CNC-machined for rigidity and long-term durability. The lightweight yet stable construction ensures consistent performance without overloading your mount.

Modular Optical Tube Design

The GS-250 includes a universal M48 extension tube allowing flexible back-focus configuration for both guiding and imaging setups.

Note: Due to limited back focus, the GS-250 may not reach focus when used with a diagonal.

AC vs AR – Focuser Options

• AC Version: Rackless (Crayford-style) focuser providing smooth manual focusing, ideal for lightweight guide cameras.
• AR Version: Rack-and-pinion focuser with increased load capacity and compatibility with ToupTek AAF electronic focusers or heavier cooled cameras.

Choose AC for lightweight manual guide setups.
Choose AR for heavier cameras or future motorised focusing upgrades.

Specifications & Compatibility

• 250mm focal length (f/5)
• 50mm aperture
• Flat-field corrected PAPO ED triplet optics
• Supports guide & planetary cameras up to 1" sensor size
• 1.25" eyepiece interface + rear M42×0.75 (T2) thread
• Multiple M5 accessory mounting points
• Dovetail base compatible with tripods & equatorial mounts
• OTA weight: 0.82kg

What's in the Box

FAQ