Premium 4-inch triplet APO refractors from established brands typically start at $2,500 and climb quickly past $3,000. The Explore Scientific ED102 FCD100 puts genuine HOYA FCD100 triplet APO optics into a 4-inch aluminum tube at the lowest price point in its class, delivering the kind of star-point precision and chromatic correction that serious visual observers and astrophotographers expect from glass at twice the price.

Key Features

• HOYA FCD100 Extra-Low Dispersion Glass – FPL-53 equivalent optics virtually eliminate false color, delivering sharp, true-to-life views of planets, double stars, and deep-sky targets in both visual and imaging use
• Air-Spaced Triplet Optical Design – Three-element configuration achieves 1.14 arcsecond resolution and diffraction-limited performance with high contrast across the field
• Durable Aluminum Optical Tube – Classic white-finish aluminum construction provides a rigid, reliable platform that holds collimation well across varying environmental conditions
• 2.5" Hexagonal Dual-Speed Focuser – Rock-solid rack-and-pinion design with 10:1 fine focus ratio supports up to 10 lbs of imaging gear with zero flex or image shift
• EMD Enhanced Multi-Layer Coatings – Proprietary broadband coatings maximize light transmission and contrast for faint deep-sky targets
• Versatile f/7 Focal Ratio – Long enough for high-magnification lunar and planetary detail, yet pairs well with a field flattener for sharp, flat-field deep-sky imaging
• Retractable Dew Shield – Blocks stray light and slows dew formation during extended sessions
• 99% Reflective 2" Diagonal Included – Premium dielectric diagonal maximizes light throughput right out of the box

Ideal For

• Astrophotographers on mid-range mounts who want sharp, well-corrected APO optics that perform on a HEQ5, Celestron AVX, or similar payload without breaking the budget
• Visual observers stepping up from doublets looking for clean, color-free views of planetary detail, tight double stars, and crisp star clusters
• Dual-purpose setups — lightweight enough to piggyback on a larger telescope as a dedicated guide scope, separating guiding and imaging for superior long-exposure performance
• Budget-conscious buyers who want genuine FCD100/FPL-53 triplet APO quality at the lowest price point available — this scope undercuts competing 4-inch triplets by $1,300 to $1,900

Accessories & Compatibility

• Explore Scientific Field Flattener (f/5–f/7) – Eliminates field curvature for sharp, flat stars edge-to-edge in deep-sky imaging — a must-have for astrophotography with this scope
• Explore Scientific 8x50 Illuminated Right Angle Polar Finder – Accurate polar alignment with an illuminated reticle for precise tracking during long exposures
• Explore Scientific Twilight I Alt-Azimuth Mount – Smooth manual tracking for visual observing sessions — a natural pairing for grab-and-go use
• Explore Scientific EXOS2-GT Equatorial Mount – GoTo motorized mount with PMC-Eight system for automated object tracking and long-exposure astrophotography
• Explore Scientific Soft-Sided Telescope Case – Padded protection for safe transport to dark-sky locations

Looking for the lightweight option? The ED102 FCD100 Carbon Fiber version shares the same optics and focuser in a carbon fiber tube that's 1.4 pounds lighter with superior thermal stability — ideal for portable setups and travel.

Note: A finder scope and carrying case are not included. The pre-installed 2N1 finder scope base accepts most standard finder scopes and guiding systems.