The GS-150 PAPO Apochromatic Guide Scope is a compact, high-precision 150mm f/5 guiding solution engineered for modern astrophotography rigs. Designed around a self-flattening PAPO ED triplet optical system, it delivers sharp, well-corrected stars across the entire field — providing reliable guide star detection and smoother mount corrections.
True Apochromatic Triplet Performance
Unlike basic finder-style or simple achromatic guide scopes, the GS-150 uses a genuine apochromatic triplet with integrated field correction. Chromatic aberration is tightly controlled, star shapes remain consistent toward the edges, and contrast is improved. The result is more accurate centroid calculation in guiding software such as PHD2, leading to tighter tracking performance during long exposures.
Optical Coatings & Contrast Control
Broadband multi-layer anti-reflection coatings maximise light transmission while precision-machined internal anti-reflection threads suppress stray light. This ensures stronger guide star signals even under light-polluted skies.
AC vs AR – What’s the Difference?
AC Version = Rackless (Crayford-Style) Focuser
The AC model uses a friction-based rackless focuser (FSB-125C). It is smooth, lightweight and ideal for standard guide cameras. This is the best choice if you are using a lightweight mono or colour guide camera and focusing manually.
AR Version = Rack & Pinion (Geared) Focuser
The AR model uses a geared rack-and-pinion focuser (FSB-125R). It offers higher load capacity, greater mechanical stability under weight, and compatibility with motor focusers. This is the better option if you plan to use heavier cooled cameras or automated focusing systems.
Which Should You Choose?
- ✔ Lightweight guide camera only → AC is sufficient
- ✔ Heavier camera or future motor focuser upgrade → Choose AR
- ✔ Building a long-term imaging rig → AR is more future-proof
Optical Performance – Spot Diagram
The spot diagram demonstrates the tight star point distribution delivered by the PAPO triplet design, confirming excellent correction across the usable field.
Key Specifications
- 150mm focal length (f/5)
- PAPO ED triplet with integrated flat-field correction
- Sharp, well-controlled star profiles across the field
- Broadband multi-layer anti-reflection coatings
- 1.25" interface with rear M42×0.75 thread
- Compatible with guide cameras up to 1" sensor size
- OTA weight: 0.59kg
- Available in AC (rackless) or AR (rack & pinion)
Mechanical Design & Dimensions
Ideal Use Case
With its wide field of view and precise optical correction, the GS-150 is particularly well suited to imaging telescopes in the 300–600mm focal length range. It also offers flexibility for planetary capture or lightweight wide-field imaging applications.
Compact, accurate and optically refined, the GS-150 is a serious upgrade from entry-level guide scopes — built for astrophotographers who expect reliable, repeatable guiding performance.
