USED GEAR INFORMATION This guide scope is in great condition. The optics appear crystal clear with no signs of imperfection. There are very minimal cosmetic imperfections on the body of the guide scope. The focuser is smooth and responsive. Description The GS Series guide scopes feature a proprietary three-element PAPO (planar apochromatic with integrated field flattener) optical configuration, incorporating a single ED element to achieve effective chromatic correction. The internal barrel is precision-machined with anti-reflection threads to suppress stray light, while all lenses are coated with multi-layer broadband AR coatings. This greatly enhances image contrast and resolution, ensuring pinpoint star images for accurate, efficient guiding, thus improving the stability of primary telescope imaging. Designed around a 1-inch flat, well-corrected image circle, the GS Series supports sensors up to the IMX533 size. Versatile in function, it can be used for star-hopping, guiding, visual observing, and even DSO imaging—making it an ideal tool for astrophotography, casual stargazing, and entry-level night-sky photography. Key Advantages 1PAPO Apochromatic Optical Design for True Star Color Reproduction The GS Series guide scopes feature a proprietary 1-inch corrected image circle, three-element PAPO (Planar Apochromatic with integrated field flattener) optical design, incorporating an ED glass element to effectively correct chromatic aberration, astigmatism, and field curvature. This design delivers high resolution and crisp, pinpoint star images. The outstanding optical performance makes the GS Series equally suited for guiding, visual observing, and entry-level astrophotography. Spot diagram of GS-250 Spot diagram of GS-350 2High-Transmission Coatings & Anti-Reflection Threads All optical surfaces are treated with broadband multi-layer AR coatings to reduce reflections and maximize light transmission. The internal barrel is precision-machined with anti-reflection threads, complemented by additional stray-light suppression measures, greatly enhancing image contrast and clarity. 3CNC Precision Machining with Fine Matte Finish The optical tube, mounting rings, and dovetail plate are crafted from aluminum alloy via CNC machining, balancing lightweight design with structural strength. Anodized surfaces provide wear and corrosion resistance suitable for field astronomy. The fine matte finish offers a comfortable, non-slip, and durable tactile experience. 4Modular Structure for Maximum Flexibility The main barrel integrates a proprietary universal M48 extension tube with built-in anti-reflection coating, enabling flexible configuration to meet different optical path requirements. This modular design supports both visual observation and astrophotography applications. Note: Due to focal length constraints, the GS250 model may not reach focus when used with a diagonal mirror. 5Dual Focusing Options for Flexibility AC Version - Rackless Focuser Smooth manual focus with Crayford-style precision; stable optical alignment; ideal for light-load astrophotography. AR Version - Rack-and-Pinion Focuser High-precision focusing with gear-and-rack drive; compatible with ToupTek Astro AAF electronic focuser; supports heavier loads and automated operation. Wide Compatibility Provides Seamless Integration ✓ Supports guide and planetary cameras with sensor sizes up to 1". ✓ Focuser end with 1.25" inner diameter and external M42×0.75 thread for direct connection to mainstream cooled cameras (recommended sensor size ≤ 1"). ✓ Multiple M5 threaded holes on the top and sides of the clamp for attaching additional astronomical accessories. ✓ Dovetail plate with multiple M6 threaded holes and one 3/8"-16 thread on the bottom for quick mounting to tripods or equatorial mounts. ✓ Universal M48 extension tube assembly with replaceable short tube for use with eyepieces or diagonals. Fully Upgraded from the FS Series Compared with the previous FS series, the GS series guide scopes bring major improvements in optical design and performance: Dimensions GS-250AC GS-250AR GS-350AC GS-350AR What's in the Box