Explore Scientific FCD1 102mm (4") ED Triplet Apochromatic Refractor OTA

Explore Scientific FCD1 102mm (4") ED Triplet Apochromatic Refractor OTA

Due to high demand and global product shortages due to the pandemic, please call for availability.

From our Moon’s chiseled craters to Jupiter’s orderly cloud belts to the blue-white stars of the Orion Nebula popping against the complex misty cloud they call home, Explore Scientific’s 102mm Apochromatic Refractor can open up a treasure trove of night sky treats.

A nice compromise between portability and aperture, this versatile high-end telescope offers true diffraction-limited optics and has an objective lens size that performs well in lunar, planetary and deep sky viewing situations.

Featuring an air-spaced triplet optical design that virtually eliminates chromatic aberrations, this telescope generates brilliant high-contrast images by combining genuine HOYA extra-low dispersion (ED) glass and proprietary EMD enhanced multi-layer coatings on all optical surfaces. This optical tube assembly includes the 99% Reflective 2-inch Diagonal Mirror with 1.25-inch Adapter, and a Cradle Ring Set with Dovetail Plate to attach to any mount that accepts Vixen style dovetail plates.


102mm (4”) aperture, 714mm focal length, f/7 focal ratio three-lens air-spaced optical system. The optics use a center lens element of Hoya FCD1 (Dense Fluoro Crown) glass, the Hoya equivalent of FPL-51 ED (Extra-low Dispersion) glass. This ED element produces superior sharpness and color correction by minimizing the chromatic aberration, the “false” color fringing seen around bright objects when light rays pass through standard crown-and-flint doublet objectives, particularly those with apertures in the ES102 class. The result is to reduce spurious color halos and fringing to vanishingly low levels.

Enhanced Multilayer Deposition (EMD™) Coatings eliminate light scatter and maintains image contrast. Contrast is further enhanced with multiple baffles that mask and deflect unwanted stray light.

This air-spaced objective is designed for precise lens centering via adjustment screws. A heavy blow or rough shipment might require an optical recentering. Removing the dew shield will give you access to the lens centering screws in the sides of the lens cell, which you can then adjust yourself by referring to the supplied instructions. You can also send your scope to Explore Scientific’s Service Center for precision alignment. A standard service charge applies for factory realignment.


High Performance Optics demand a high precision focuser. Perfect focus is easily achieved with the standard-equipment ten-to-one, dual-speed focuser.

This is especially true when observing at high magnification or when making CCD images. With a standard focuser, you will find that a tiny nudge will throw out focus and turn your night into one of frustration.

To protect against marring of accessories, the focuser and included 2" to 1.25" adapter incorporate compression rings for sure grip.

Dew Shield

The supplied fixed dew shield slows the formation of dew or frost on the lens in damp conditions to extend your observing time. It also improves the contrast, in the manner of a lens shade on a camera lens. A slip-on metal dust cap for the optical tube is standard.

Star Diagonal

The 2" dielectric diagonal provided as standard equipment includes a 1.25" eyepiece holder adapter and dust covers to protect the mirror. This diagonal incorporates a light-weight, one-piece diagonal body that securely cradles the precision polished diagonal flat mirror, insuring precision alignment. Ultra-high reflective coatings (99% reflective) composed of multiple thin layers of dielectric material delivers maximum light throughput.

Both 2" and 1.25" eyepiece holders use compression rings instead of a simple set-screw to more securely hold your valued eyepiece or imaging device, and to prevent the eyepiece or camera barrel from being scoring. You can thread standard 48mm filters into the 2" barrel or the 1.25" adapter.

Mounting rings and dovetail

The ES102 has dual split mounting rings with a dovetail plate that fits the Vixen-style dovetail slot on the head of many of the most popular medium capacity German equatorial mounts. Such mounts include the Celestron Advanced VX go-to equatorial, the Meade LXD-75 or LX-80 go-to equatorials, and the Vixen Sphinx and Great Polaris Deluxe equatorial mounts, among others. A spacer/stabilizing bar on the top of the rings provides a carrying handle that makes it easy to transport the optical tube and install it on your equatorial mount. There is a mounting shoe for an optional finderscope installed on the body of the scope.

Free Extended Warranty

Register Your Explore Scientific Telescope in Canada or the USA and receive a free Lifetime Extended Warranty.

All Explore Scientific telescopes and telescope accessories are covered under the Explore Scientific USA One Year Limited Warranty against defects with proof of purchase, but you can extend this limited warranty to the Explore STAR Transferable Extended Life of the Product Warranty by simply filling out the product registration and submitting it in within 60 days.


  • Air-spaced triplet featuring genuine HOYA™ FCD1 Extra-low Dispersion glass
  • 2" dual-speed focuser
  • 2" Dielectric star diagonal
  • Aluminum optical tube
  • Tube rings and Vixen style dovetail


  • Aperture: 102mm (4")
  • Focal length: 714mm (28.1")
  • Focal ratio: f/7
  • Lens construction: Air-spaced triplet APO, HOYA™ FCD1 low-dispersion glass
  • Optical coatings: Explore EMD
  • 2" dual-speed focuser with compression ring
  • Tube rings and dovetail, fits 44mm (1.75") dovetail saddles
  • Finderscope mounting base included
  • Camera Capable:
    • USB imagers
    • All-in-one cameras via universal digital camera adapter
    • DSLR/SLR (Requires T2 ring, 2" prime focus adapter)
    • Above cameras and adapters sold separately
  • Length without dew shield: 60.3cm (30.5")
  • Length with dew shield: 77.4cm (23.8")
  • Weight 5kg (11lbs)
  • Color: White with black accents
  • Explore Scientific One Year Warranty, free upgrade to Explore STAR Transferable Extended Life of the Product Warranty with registration within 60 days