Comparing Explore Scientific's AR102 vs ED102 vs ED102-FCD100

TL;DR: Quick Summary▾

The AR102 vs ED102 vs ED102-FCD100 comparison centers on the biggest difference between these three refractors: the glass. Same 102mm aperture, same manufacturer, three different optical levels. The AR102 ($449.99) is a solid achromatic doublet for visual observing. The ED102 ($999.99) upgrades to a Hoya FCD1 triplet that opens the door to astrophotography. The ED102-FCD100 ($1,699.99) uses Hoya FCD100 glass for near-perfect color correction and adds a premium 2.5" hexagonal focuser.

Most telescope comparisons mix aperture sizes, manufacturers, and designs, which makes it hard to tell what's actually driving the differences. This comparison is different. All three scopes share the same 102mm aperture, the same Explore Scientific build philosophy, and the same basic refractor layout. The biggest change is the optical design: achromatic doublet, ED triplet, and FCD100 triplet. The focusers and focal lengths differ too (see the table below).

That makes it a useful look at what glass quality and element count buy you in visual performance, astrophotography capability, and total value. For a broader look at how achromatic and apochromatic refractors differ in general, see our APO vs achromatic refractor guide.

Overview: Three Levels of 102mm Refractor

AR102 — The Achromatic Doublet

The Explore Scientific AR102 uses a two-element air-spaced objective with standard crown and flint glass. It's a classic achromatic doublet at f/6.5, a fast focal ratio that delivers wide fields of view but produces noticeable chromatic aberration on bright targets.

At $449.99, this is the entry point for a serious 102mm refractor with a quality 2" dual-speed Crayford focuser, full multi-coatings, and a 2" dielectric diagonal. Explore Scientific publishes no MSRP, so the prices in this comparison are retail; check the product page for the current price.

ED102 — The FCD1 Triplet

The Explore Scientific ED102 steps up to a three-element air-spaced apochromatic design using Hoya FCD1 extra-low-dispersion glass. FCD1 is equivalent in performance to the widely referenced Ohara S-FPL51, an ED glass with an Abbe number around 81.5, which significantly reduces chromatic aberration compared to standard glass.

At $999.99, the ED102 operates at f/7 with a 714mm focal length. It includes a 2" rack-and-pinion focuser with extension tubes and a retractable dew shield.

ED102-FCD100 — The Premium Triplet

The Explore Scientific ED102-FCD100 uses the same three-element layout but substitutes Hoya FCD100 glass, a super-ED glass with an Abbe number of 95.1. That's a substantial jump from FCD1's ~81.5, putting it in the same optical performance class as fluorite crystal.

At $1,699.99, the FCD100 version shares the f/7, 714mm focal length but upgrades to a heavy-duty 2.5" hexagonal focuser rated for 10 lbs of imaging payload. There's also a carbon fiber version ($1,899.99) that drops the weight from 12 lbs to 9.5 lbs.

AR102 vs ED102 vs ED102-FCD100 Comparison: Head to Head

Optical Design and Glass: What's Actually Different

The defining difference between these three scopes is how they handle chromatic aberration, and that comes down to the glass.

AR102: Crown and Flint

The AR102's doublet pairs a positive crown glass element with a negative flint glass element. This classic combination brings two wavelengths of light (red and blue) to a common focus, correcting the most severe chromatic aberration. But the secondary spectrum (the residual color error between the corrected wavelengths) remains. At f/6.5, this secondary spectrum is clearly visible as a violet fringe around bright objects.

The faster focal ratio is a double-edged sword: you get wider fields of view and shorter exposure times, but the chromatic aberration is more pronounced than it would be at a slower ratio like f/10.

ED102: Hoya FCD1 Triplet

The ED102's triplet uses Hoya FCD1 glass, an extra-low-dispersion glass that bends light with far less wavelength-dependent spread than standard crown glass. With three elements working together, the ED102 brings three wavelengths closer to a common focus, dramatically reducing secondary spectrum.

The improvement over the AR102 is immediately visible at the eyepiece. Bright stars show tight, clean Airy disks. Planetary limbs have minimal color fringing. The residual CA that remains is primarily a faint blue-violet haze visible only on the brightest targets at high magnification.

Hoya FCD1 is functionally equivalent to Ohara's S-FPL51, the glass referenced in many "ED" telescope reviews. It's a genuine extra-low-dispersion glass: a significant step above standard optics, though not in the super-ED category.

ED102-FCD100: Hoya FCD100 Triplet

The FCD100 version substitutes Hoya FCD100 glass, which has an Abbe number of 95.1 compared to FCD1's ~81.5. In practical terms, this means the FCD100 disperses light far less than FCD1, so the triplet can achieve tighter color correction across a broader range of wavelengths.

The result at the eyepiece: virtually no false color on any target. Bright stars are clean white pinpoints. Jupiter's limb is sharp with virtually no color fringing. In astrophotography, stars render as tight, round dots without the blue bloat of a less-corrected objective.

Hoya FCD100 performs in the same league as fluorite crystal (CaF2, Abbe number ~95.2) and Ohara's S-FPL53 (Abbe number 94.9).

Chromatic Aberration: What You'll Actually See

Here's what to expect from each scope at the eyepiece, based on its glass and focal ratio:

The Moon

• AR102: Bright limb shows a noticeable violet-blue fringe, especially at 100x and above. Interior detail (craters, rilles, maria boundaries) is sharp. A minus-violet filter cleans up the color fringing significantly.
• ED102: Limb fringe is faint: a slight blue haze visible at high power if you look for it. Interior detail is crisp with excellent contrast.
• ED102-FCD100: Clean limb with virtually no visible color fringing at any magnification. Maximum contrast on fine detail.

Jupiter and Saturn

• AR102: Violet halo around the planet disk, particularly noticeable at the limb against dark sky. Cloud belt detail is good but slightly washed by the color fringe. Cassini division on Saturn is visible but not as crisp.
• ED102: Minimal color fringe. Cloud belts are sharp with good color fidelity. Cassini division is clean. The view is significantly better than the AR102.
• ED102-FCD100: Virtually no false color. Maximum contrast on cloud belt detail. Cassini division is knife-sharp.

Deep-Sky Objects

• AR102: Chromatic aberration is far less noticeable on dim objects. Open clusters, nebulae, and galaxies look very similar across all three scopes at the same magnification. The AR102's f/6.5 focal ratio actually gives it a slightly wider true field of view than the two f/7 triplets.
• ED102: Marginally sharper star points in clusters. The improvement over the AR102 is subtle on most deep-sky targets.
• ED102-FCD100: Same as ED102 for deep-sky: the premium glass pays its biggest dividends on bright targets, not faint ones.

Astrophotography Performance

This is where the three scopes diverge most dramatically.

AR102: Limited

The AR102 is not designed for serious astrophotography. The chromatic aberration that's manageable at the eyepiece becomes a significant problem in stacked images. Stars develop purple halos, and bright objects show color fringing that's difficult to remove in processing. Lunar and planetary imaging (short exposures) is feasible with a UV/IR cut filter, but broadband (full-color) deep-sky imaging with the AR102 will always be fighting the color.

ED102: Capable

The ED102 is where astrophotography becomes genuinely practical. The FCD1 triplet produces tight star images with minimal color bloat. Deep-sky images come out clean enough that minor residual CA can be managed in post-processing. The 2" rack-and-pinion focuser holds position well under camera loads, and the f/7 focal ratio provides a good balance between image scale and exposure time.

Paired with a field flattener, the ED102 delivers very good results on nebulae, galaxies, and star clusters.

ED102-FCD100: Excellent

The FCD100 glass virtually eliminates chromatic aberration in images. Stars are tight, round dots, out to the edges once a field flattener is added. Colors are accurate, without the blue halos of a less-corrected objective. The 2.5" hexagonal focuser is a major upgrade for imaging: its rigid design is rated for camera-and-filter-wheel combinations up to 10 lbs, and the hex profile resists rotation during focusing.

This is the scope we'd point imagers toward when they want to spend their time imaging instead of correcting optical artifacts in post. For those prioritizing imaging payload and portability, the carbon fiber version ($1,899.99) shaves 2.5 lbs off the OTA, which translates directly to more margin on your mount's payload capacity.

Build Quality and Focusers

All three scopes share Explore Scientific's build standards: fully multi-coated optics and an objective cell you can collimate. The differences are in the details.

Focuser Comparison

The focuser upgrade from the ED102 to the ED102-FCD100 matters more than it might seem. A focuser that shifts or rotates under the weight of a camera, filter wheel, and off-axis guider can ruin an entire night of imaging. The 2.5" hex focuser on the FCD100 version is specifically designed for this use case.

Included Accessories

• AR102: 2" dielectric diagonal, 1.25" eyepiece adapter, 8x50 straight-through finderscope, finder scope base, mounting cradle with Vixen dovetail
• ED102: 99% reflective 2" diagonal, 1.25" eyepiece adapter, 2N1 finder scope base, two extension tubes, cradle rings with handle, Vixen dovetail
• ED102-FCD100: 99% reflective 2" diagonal, 2" and 1.25" eyepiece adapters, 2N1 finder scope base, two extension tubes, cradle rings with handle, Vixen dovetail

All three models now include a diagonal in the box. The AR102 is the only one that ships with an actual finderscope (8x50); the triplet models include a finder scope base but no finder optic, so budget for one separately.

The Value Equation: What Each Upgrade Gets You

Thinking about which 102mm refractor to buy? Here's what each step up the ladder actually delivers:

AR102 to ED102 ($449.99 to $999.99 — $550 more)

This $550 buys you:

• Triplet vs. doublet optics — The single biggest optical upgrade. Moving from two elements in standard glass to three elements with ED glass dramatically reduces chromatic aberration.
• Astrophotography capability — The AR102 can't produce clean broadband (full-color) deep-sky images; the ED102 can.
• Better planetary contrast — Less false color means sharper, more accurate views of Jupiter's cloud belts, Saturn's rings, and lunar detail.
• Slightly longer focal length — 714mm vs 663mm, giving marginally higher magnification per eyepiece.

This is the biggest performance jump of the two upgrades. If you're choosing between the AR102 and ED102, and you have any interest in imaging, the ED102 is worth the additional investment.

ED102 to ED102-FCD100 ($999.99 to $1,699.99 — $700 more)

This $700 buys you:

• Premium glass — Hoya FCD100 (Abbe 95.1) vs. FCD1 (Abbe ~81.5). Virtually eliminates residual CA that FCD1 still shows on bright targets.
• Heavy-duty focuser — 2.5" hexagonal design rated for 10 lbs, resistant to rotation. A genuine imaging-grade upgrade.
• Tighter star images — In astrophotography, the difference is cleaner star colors and less post-processing work.

This upgrade is most valuable if you're a serious astrophotographer or a dedicated planetary observer who wants the best color correction of these three scopes. For visual deep-sky observing, the difference from the ED102 is subtle.

Is the Carbon Fiber FCD100 Worth the Extra $200?

The ED102-FCD100 CF ($1,899.99) uses the same FCD100 optics and hexagonal focuser but wraps them in a carbon fiber tube. The benefits:

• Weight savings: 9.5 lbs vs 12 lbs, a 2.5 lb reduction that matters when your imaging rig pushes mount payload limits.
• Thermal stability: Carbon fiber does not contract as temperatures drop the way aluminum does, but the lens itself shortens its focal length as it cools, so expect to refocus during long imaging sessions with either tube.

At just $200 more than the aluminum version, the carbon fiber upgrade is an easy call for astrophotographers. The weight savings alone justify the modest premium. For visual-only use, the aluminum version is still the better value.

Final Verdict: Which Should You Choose?

Choose the AR102 ($449.99) if:

• You observe visually and don't plan to do deep-sky astrophotography
• You want 102mm of quality optics at the lowest cost
• Your targets are primarily deep-sky objects, where chromatic aberration is least visible
• You're building a grab-and-go visual setup where the included 8x50 finderscope adds value

Choose the ED102 ($999.99) if:

• You want to do astrophotography and need clean star images
• You want a significant visual upgrade for planetary and lunar observing
• You want a versatile scope that works well for both visual and imaging
• You want an apochromatic triplet at the lowest price in this comparison

Choose the ED102-FCD100 ($1,699.99) if:

• Astrophotography is your primary use and you want the cleanest possible star images
• You need a heavy-duty focuser that handles serious imaging payloads
• You want near-zero chromatic aberration for demanding planetary observing
• You're building a long-term imaging setup and want a scope you won't outgrow

For a broader comparison of achromatic vs apochromatic refractor technology, see our APO vs achromatic refractor guide.

Frequently Asked Questions

Can the AR102 do any astrophotography at all?▾

Yes. Lunar and planetary imaging is feasible with short exposures and a UV/IR cut filter, although the violet fringe still shows on bright limbs, as it does at the eyepiece. Narrowband deep-sky imaging (Ha, OIII, SII) is also feasible since each filter isolates a narrow band of wavelengths, sidestepping the CA problem.

What's the difference between Hoya FCD1 and FCD100 glass?▾

Both are extra-low-dispersion glasses from Hoya, but they're in different performance tiers. FCD1 has an Abbe number around 81.5, making it a standard ED glass equivalent to Ohara's S-FPL51. FCD100 has an Abbe number of 95.1, putting it in the "super-ED" category alongside Ohara's S-FPL53 and fluorite crystal. The higher Abbe number means FCD100 disperses light significantly less, resulting in tighter color correction.

Do the ED102 and ED102-FCD100 need a field flattener for imaging?▾

For most astrophotography, yes. Like any refractor without a built-in flattener, these scopes exhibit some field curvature: the edges of the image aren't perfectly flat without a corrector. Explore Scientific makes compatible field flatteners for both models. For visual use, field curvature isn't a concern since your eye accommodates it naturally.

How much heavier is the FCD100 version than the standard ED102?▾

The ED102-FCD100 weighs 12 lbs against the ED102's 9.62 lbs, so plan on about 2.4 lbs more mount payload. The carbon fiber version brings it down to 9.5 lbs.

Which mount do I need for these scopes?▾

For visual use, all three work well on a mid-range alt-azimuth mount like the Twilight I. For astrophotography, you'll need an equatorial mount rated for at least 25–30 lbs total payload (scope + camera + accessories). The lighter carbon fiber FCD100 (9.5 lbs) gives you the most imaging payload margin.

Is the ED102 the same glass as the ED80?▾

Yes. Both the ED80 and ED102 from Explore Scientific use Hoya FCD1 extra-low-dispersion glass in a triplet configuration. The ED102 simply provides more aperture (102mm vs 80mm), which means more light-gathering power, higher resolution, and brighter images. The color correction per unit of aperture is equivalent.