Explore Scientific ED102-FCD100 Series Triplet APO Refractor

True Apochromatic Optics: An FCD100 Air-Spaced Triplet

At the core of the ED102-FCD100 is an advanced air-spaced triplet objective lens. This design utilizes a central element made from genuine HOYA FCD100, an extra-low dispersion (ED) glass with optical properties comparable to pure fluorite. Together with a high refractive index element, this triplet design achieves a true apochromatic level of performance, virtually eliminating the chromatic aberration (false color) that can compromise image contrast and sharpness in simpler designs.

You will see the difference on high-contrast targets. Bright stars like Vega resolve as sharp pinpoints without distracting purple halos, and the lunar limb appears crisp and well-defined against the blackness of space. The optics are diffraction-limited, with Explore Scientific's proprietary EMD enhanced multi-layer coatings on all optical surfaces, for brilliant, high-contrast views of the Moon, planets and deep-sky objects.

A Versatile f/7 System: 102mm Aperture and 714mm Focal Length

The ED102-FCD100's optical specifications create a powerful and flexible instrument. The 102mm (4") aperture gathers enough light to reveal faint details in galaxies and resolve globular clusters, while its diffraction-limited optics can deliver stunning planetary and lunar views. This aperture class represents a significant step up from smaller 80mm refractors, providing a noticeable increase in brightness and resolution without a major penalty in size or weight.

The 714mm focal length results in an f/7 focal ratio, a modern sweet spot for refractors. This ratio is fast enough for efficient deep-sky imaging while remaining forgiving of eyepiece designs and maintaining excellent visual contrast. It still provides the image scale needed to achieve high magnifications for resolving detail on Jupiter's cloud bands or the Cassini Division in Saturn's rings.

2.5" HEX Focuser: 10 lbs of Imaging-Grade Stability

The ED102-FCD100 is equipped with a 2.5" hexagonal rack-and-pinion focuser. The precision 2.5" HEX focuser offers smooth, stable focusing and supports imaging setups up to 10 lbs (4.5 kg).

Focusing is smooth and precise thanks to the dual-speed mechanism, which allows for coarse adjustments to find initial focus and micro-adjustments to achieve critical sharpness.

Optimized for Visual Observing with a 99% Reflective 2" Diagonal

While built for imaging, the ED102-FCD100 is also a fine visual instrument. Included in the package is a 99% reflective 2" diagonal. This ensures that the maximum amount of light from the objective reaches your eye, preserving the brightness and contrast of the image. The 2" format allows you to use wide-field 2" eyepieces to take full advantage of the telescope's ability to frame large star fields and nebulae.

For added flexibility, a 1.25" adapter is included, making the telescope compatible with the vast range of standard 1.25" eyepieces. This allows you to easily switch to higher-power planetary eyepieces or use specialized 1.25" filters. The combination of the apochromatic optics and the high-quality diagonal delivers breathtaking views of everything from the Moon and planets to the most delicate deep-sky objects.

Astrophotography with the ED102-FCD100

The ED102-FCD100 is a formidable platform for astrophotography. Its f/7 focal ratio and 714mm focal length are ideal for a wide range of celestial targets, from expansive emission nebulae to distant galaxy clusters. The apochromatic optics keep stars small and tight with virtually no violet bloating, resulting in images with excellent color fidelity and high resolution.

Like other refractors, the bare tube has a curved focal plane, so sharp stars toward the corners of a larger sensor call for a corrector. Two correctors are available for the FCD100-10207-02: the 0.8x Focal Reducer (ES-FR0.8x), which turns the 714 mm focal length into 571 mm and f/7 into f/5.6, with 55 mm (+/- 2 mm) of back spacing and a thread for a standard 42 mm T-ring; and the Field Flattener for f/5 to f/7 refractors (ES-FF2F5/F7), which does not change the focal length, needs 55 mm (+/-2 mm) of spacing to the sensor and is for photographic use only.

ED102 Triplet vs. Standard ED Doublet Refractors

While a quality ED doublet refractor provides a significant improvement over a basic achromat, it still exhibits a small but measurable amount of residual chromatic aberration. The Explore Scientific ED102-FCD100's triplet design is specifically engineered to correct this remaining false color for a tangible increase in performance.

• For Astrophotography: The triplet's superior color correction produces smaller, more concentrated star images free from blue or violet bloat. This allows for more accurate color data acquisition, captures finer stellar detail,.
• For Visual Observing: When pushing magnification on bright targets like Jupiter, Venus, or the lunar limb, the triplet's near absence of color fringing delivers a sharper, higher-contrast image. This makes it easier to resolve subtle details, such as delicate festoons in Jupiter's atmosphere or tiny craterlets on the Moon's surface.

Engineered for the Field: Tube, Dew Shield, and Mounting

The ED102-FCD100 is built for practical use under the stars. A retractable dew shield extends to 774 mm to minimize moisture formation on the objective lens during long nights and to block off-axis light from degrading the image. When retracted, the tube length is a compact 603 mm for easy transport and storage.

The telescope attaches to any compatible mount via a standard Vixen-style dovetail bar. Also included is Explore Scientific's Hybrid Finder Scope Base, which is designed to accept a wide variety of finder scope brackets, including Explore Scientific's own and those using the common Vixen/Synta-style mini-dovetail, giving you flexibility in your choice of aiming device.

The 12 lb ED102 as a "Grab-and-Go" Instrument

Weighing in at just 12 lbs (5.4 kg), the ED102-FCD100 optical tube is remarkably portable for a 4" apochromatic triplet. This light weight makes it an ideal "grab-and-go" telescope when paired with a medium-duty equatorial mount. It is easy to set up and transport to a dark sky site, yet it offers the optical power to make the trip worthwhile.

This portability also enhances its versatility. The ED102 can also serve as an auxiliary scope on larger instruments, for guiding and imaging versatility. Its combination of high-end optical performance and manageable weight makes it a valuable and flexible addition to any astronomer's equipment collection.