Finding a 4-inch triplet APO refractor under $1,000 used to be impossible — the optics alone typically cost more than that. The Explore Scientific ED102 Essential Series is the only 102mm air-spaced triplet APO refractor available under $1,000, delivering diffraction-limited optics with HOYA FCD1 extra-low dispersion glass that produces the color-free, high-contrast views visual observers and astrophotographers demand at this aperture.

Key Features

• HOYA FCD1 Extra-Low Dispersion Glass – S-FPL51 equivalent ED glass in a three-element design minimizes chromatic aberration, delivering clean, true-color views with excellent contrast across the field
• Air-Spaced Triplet Optical Design – Three-element apochromatic configuration achieves 1.14 arcsecond resolution and diffraction-limited performance guaranteed at 0.25 PV or better
• Aluminum Optical Tube – Rigid construction with flat-black interior coatings and internal baffles for maximum contrast and stray-light suppression
• 2" Dual-Speed Rack-and-Pinion Focuser – Smooth, rotatable focuser with 10:1 fine focus ratio for precise adjustments during both visual and imaging sessions
• EMD Enhanced Multi-Layer Coatings – Proprietary broadband coatings on all air-to-glass surfaces maximize light transmission and contrast
• Versatile f/7 Focal Ratio – Long enough for high-magnification lunar and planetary detail, yet pairs well with a field flattener for 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

• Visual observers who want true apochromatic performance — sharp, color-free views of Jupiter's cloud bands, Saturn's rings, and tight double stars — without the $1,200+ price tag of FCD100/FPL-53 triplets
• Beginning astrophotographers stepping into refractor imaging with a DSLR or dedicated camera — the triplet design produces cleaner star profiles than any doublet at this price, and the f/7 ratio is forgiving to work with
• Budget-conscious astronomers who want the sharpest possible 4-inch optics for under $700 — competing triplet APOs start at $1,200 and up
• Upgraders from achromats or doublet EDs ready for the next level of color correction and contrast without jumping to the $1,200–$3,000 premium triplet tier

Accessories & Compatibility

• Explore Scientific Field Flattener (f/5–f/7) – Eliminates field curvature for sharp, flat stars edge-to-edge in deep-sky imaging — recommended 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

Ready for the imaging upgrade? The ED102 FCD100 steps up to HOYA FCD100 glass (Abbe 95.10 vs 81.61) and a heavier-duty 2.5" hexagonal focuser rated for 10 lbs of imaging gear — the choice for serious astrophotographers who need near-zero chromatic aberration.

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.