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Explore Scientific FCD100 Series 127mm f/7.5 Triplet APO Refractor - Aluminum with 2.5" HEX Focuser

SKU ES-FCD100-127075-02
Original price $2,499.99 USD - Original price $2,499.99 USD
Original price
$2,499.99 USD
$2,499.99 USD - $2,499.99 USD
Current price $2,499.99 USD
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  • 127mm (5") Aperture
  • f/7.5 Focal Ratio / 952mm Focal Length
  • Air-Spaced Triplet Apochromatic Optics
  • HOYA FCD100 ED Glass Element
  • 2.5" Hexagonal Rack-and-Pinion Focuser
  • 10 lbs (4.5 kg) Focuser Load Capacity
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See exactly how your targets fit with the Explore Scientific FCD100 Series 127mm f/7.5 Triplet APO Refractor - Aluminum with 2.5" HEX Focuser, on real sky survey data.

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  • Explore Scientific FCD100 Series 127mm f/7.5 Triplet APO Refractor - Aluminum with 2.5" HEX Focuser

    The Explore Scientific FCD100 Series 127mm f/7.5 Triplet APO Refractor combines a large, diffraction-limited objective with premium HOYA FCD100 ED glass to deliver razor-sharp, high-contrast images. Its 952mm focal length provides a versatile balance for both planetary and deep-sky work, while the robust 2.5" HEX focuser supports imaging payloads up to 10 lbs (4.5 kg). With an air-spaced triplet optical design housed in a 130mm diameter aluminum tube, this refractor is designed for serious visual observers and astrophotographers.

    FCD100 Triplet Optics: A 127mm Apochromatic Objective

    At the heart of this refractor is a 127mm (5") air-spaced triplet objective featuring a genuine HOYA FCD100 glass element. This extra-low dispersion (ED) material provides color correction equivalent to fluorite, virtually eliminating chromatic aberration. The result is images with virtually no false color or purple fringing around bright stars, planetary limbs and the lunar terminator.

    Explore Scientific combines the FCD100 glass with its proprietary EMD enhanced multi-layer coatings and describes the optics as diffraction-limited, for razor-sharp, high-contrast views of the Moon, planets and deep-sky objects, including delicate nebular structure and pinpoint star fields.

    The f/7.5 Advantage: 952mm Focal Length for Planets and Deep Sky

    The telescope's 952mm focal length and f/7.5 focal ratio create a highly versatile instrument. This combination offers enough magnification for resolving fine details on Jupiter's cloud bands and the Cassini Division in Saturn's rings, without making the instrument too specialized for wider-field targets. The 127mm aperture gathers enough light to make faint deep-sky objects pop, providing bright views of globular clusters and planetary nebulae.

    For visual observers, this focal ratio works well with a wide range of eyepieces, from low-power 2-inch eyepieces for sweeping the Milky Way to high-power planetary eyepieces for detailed solar system work. For imagers, f/7.5 is a solid starting point that can be adapted with optional focal reducers to capture larger targets or with Barlow lenses to increase the image scale for planets.

    2.5" HEX Focuser: A Rigid Platform for a 10 lb Imaging Train

    A focuser for astrophotography has to carry the camera and its accessories. This refractor is equipped with a 2.5" hexagonal rack-and-pinion focuser, which is robust, offering smooth, precise adjustments.

    It can support heavy imaging setups up to 10 lbs (4.5 kg). The smooth, precise motion helps with the fine focus adjustments that planetary and deep-sky imaging need.

    Field-Ready Ergonomics: Aluminum Tube and Integrated Dew Shield

    The aluminum optical tube is engineered for both durability and practical use in the field. Measuring 849mm with the dew shield retracted, the telescope is manageable for transport and setup. Several integrated features minimize setup time and improve your observing sessions.

    • Retractable Dew Shield: An integrated dew shield extends to 1060mm, preventing moisture from forming on the objective lens during long nights and blocking stray light from nearby sources that could degrade image contrast.
    • Cradle Ring & Handle: The included cradle ring assembly provides a secure mounting point and features a top-mounted handle, making the optical tube easy to carry, lift, and mount onto your dovetail saddle.
    • Finder Scope Base: A Hybrid Finder Scope Base is included, designed to accept both legacy Explore Scientific finders and standard Vixen-style finder scope brackets.

    Vixen-Style Dovetail and Cradle for Easy Mounting

    The telescope comes ready to attach to a wide range of equatorial mounts thanks to the included Vixen-style (V-style) dovetail plate. This universal mounting standard ensures out-of-the-box compatibility with many of the most popular mounts used by amateur astronomers. The dovetail attaches securely to the base of the cradle ring assembly, providing a stable connection to your mount head.

    The cradle ring with its carry handle and the Vixen-style dovetail plate come with the telescope, so you can get it onto your mount and start observing quickly.

    A 99% Reflective 2" Diagonal for High-Contrast Views

    For visual observers, the quality of the star diagonal is just as important as the main objective. Explore Scientific includes a 99% reflective 2" diagonal. This ensures that the maximum amount of light from the objective reaches your eyepiece, resulting in brighter images and improved contrast. The diagonal provides a comfortable 90-degree viewing angle and includes a 1.25" adapter, allowing you to use both 2" and 1.25" eyepieces and accessories.

    HOYA FCD100 vs. FPL-53: Understanding Apochromatic Glass

    In the world of premium apochromatic refractors, two glass types are renowned for their exceptional color correction: Ohara FPL-53 and HOYA FCD100. Both are extra-low dispersion glasses that let optical designers bring the colors of the visible spectrum close to a common focus. Choosing between them is less about one being universally superior and more about the specific optical design it enables and the skill of the optician.

    HOYA FCD100 is the apex of the FCD family, with performance equivalent to fluorite, and the triplet virtually eliminates chromatic aberration. For an observer or imager, that means razor-sharp, high-contrast views without the false color that softens details.

  • How does the Explore Scientific FCD100 127mm APO perform on planets like Jupiter and Saturn?

    This refractor excels at revealing fine planetary detail. The 127mm aperture resolves fine details, while the apochromatic FCD100 optics give high contrast with virtually no false color. You can expect to clearly see Jupiter's main cloud bands, the Great Red Spot, and the Cassini Division in Saturn's rings under steady seeing conditions.

    Is the Explore Scientific 127mm Triplet suitable for imaging a large nebula like the North American Nebula (NGC 7000)?

    Yes, but you will likely need a focal reducer. At its native 952mm focal length (f/7.5), the telescope is well-suited for smaller nebulae and galaxies. To fit very large objects like the North American Nebula or the Andromeda Galaxy (M31) into a single frame, adding an optional focal reducer/flattener is recommended to widen the field of view.

    What kind of mount is required for the Explore Scientific FCD100 127mm APO?

    The optical tube's weight and length require a stable mount. For visual use, a medium-duty equatorial mount is sufficient. For astrophotography with a full imaging train, choose a more robust mount whose imaging capacity comfortably exceeds the total weight of the telescope and accessories.

    What is the benefit of the 2.5" HEX focuser on the FCD100 127mm?

    The 2.5" HEX focuser uses a hexagonal drawtube and a rack-and-pinion mechanism. It is robust, with smooth, precise adjustments, and can support heavy imaging setups up to 10 lbs (4.5 kg).

    How does HOYA FCD100 glass compare to FPL-53 in this refractor?

    HOYA FCD100 and Ohara FPL-53 are considered functional equivalents in their ability to correct for chromatic aberration. Both are premier ED glass types that, when used in a triplet objective lens design, produce a true apochromatic image with virtually no color fringing. Explore Scientific compares FCD100 with Ohara FPL-53 and with fluorite.

    Can I use 2" eyepieces and accessories with the Explore Scientific 127mm FCD100?

    Yes. The telescope includes a 99% reflective 2" diagonal, which takes 2" eyepieces. A 1.25" adapter is also included with the diagonal for use with smaller format eyepieces.

    Does the Explore Scientific FCD100 127mm need a field flattener for astrophotography?

    Like other refractors, it has some field curvature, so round stars toward the corners of a larger sensor call for a field flattener or reducer/flattener. Stars in the center are sharp without one.

    What is the first thing I should do when setting up the FCD100 127mm for the first time?

    First, securely mount the optical tube to your equatorial mount using the Vixen-style dovetail. Once outside, let the telescope adjust to the outdoor temperature before observing at high power. Then insert the 2" diagonal and a low-power eyepiece to align your finder scope during the daytime on a distant, stationary object like a treetop or telephone pole.

    Is the carrying handle on the FCD100 127mm strong enough to lift the telescope?

    Explore Scientific supplies the cradle ring with a carry handle, meant for carrying the optical tube and lifting it onto and off the mount.

    What is a Hybrid Finder Scope Base?

    The included Hybrid Finder Scope Base is designed by Explore Scientific to be versatile. It accepts both their own legacy finder scope brackets and the more common mini-dovetail type brackets used by brands like Vixen, Synta, and Celestron, giving you flexibility in choosing a finder scope.

  • Optical Design Air-Spaced Triplet Apochromatic Refractor
    Aperture 127mm (5")
    Focal Ratio f/7.5
    Glass Type HOYA FCD100 ED Glass
    Focuser 2.5" Hexagonal Rack-and-Pinion
    GTIN 812257017621
    Focal length 952mm
    Focuser load capacity 10 lbs (4.5 kg)
    Tube length (retracted) 849 mm (1060 mm with dew shield)
    Tube outer diameter 130 mm
    Dovetail included Vixen-Style
    Mount included No (optical tube only)
    • FCD100 127mm OTA with 2.5" HEX focuser and integrated dew shield

      × 1

    • Cradle ring with carry handle

      × 1

    • Vixen-style dovetail plate

      × 1

    • 99% reflective 2" diagonal with 1.25" adapter

      × 1

    • Hybrid Finder Scope Base ES-FB2N1-00

      × 1

  • Explore Scientific Warranty