Explore Scientific 102mm f/7 "Essential Series" FCD-1 ED Triplet Refractor


Availability: In stock

This 102mm (4") Explore Scientific Essential Series air-spaced ED triplet apochromatic refractor is loaded with quality optical performance at a surprisingly reasonable price for a scope of its size and optical quality.
Our Product #: ES102B
Explore Scientific Product #: ES-ED10207-01
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Product Description

This 4" Explore Scientific ES102 "Essential Series" apochromatic refractor has:
102mm f/7 fully multicoated triplet optics using a Hoya FPL51-equivalent ED element
Dual-speed 2" rack and pinion focuser with 10:1 ratio fine focusing
Mounting rings with dovetail for use on a Vixen-style altazimuth or German equatorial mount
Finderscope base installed on OTA
Extended product lifetime warranty
2" 99% reflective dielectric star diagonal

The Explore Scientific 4" (102mm) aperture "Essentials Series" ES102 ED triplet refractor uses a premium Hoya ED glass element and state-of-the-art optical multicoatings in its apochromatic air-spaced ED triplet optics. The result is images that are essentially free of the annoying halo of unfocused violet light (chromatic aberration) that mars the view of bright stars and solar system objects in lesser scopes, despite the scope's relatively large aperture, and even at very high magnifications.

The Explore Scientific ES102 is a natural on an equatorial mount as the heart of your primary observing system. In addition, it's an excellent astrograph for serious wide field imaging, as well as crisp solar system imaging. Considering its lifetime warranty, its surprisingly reasonable price for a 4" apochromatic triplet, and in view of the great optical performance that comes as standard equipment, the 4" Explore Scientific ES102 is a terrific buy!

Features of this Telescope . . .

ED triplet refractor optics: 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 Fluor 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.

Fully multicoated optics: The ES102 triplet objective lens has EMD™ (Enhanced Multilayer Deposition) antireflection multicoatings on all air-to-glass surfaces for high light transmission, minimal light scatter, and excellent contrast.

Internal light baffles: The aluminum tube body has contrast-enhancing internal light baffles and a specially darkened tube interior to provide dark sky backgrounds and high contrast.

Collimatable optics: One of the bonuses of owning a refractor is that, compared to standard reflector telescopes, they almost never require realigning of the optics (collimation). However, any air-spaced refractor telescope may require optical recentering if the lens elements are knocked out of alignment by a heavy blow during shipping or use. 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.

Dew shield: The supplied dew shield slows the formation of dew on the lens in cold weather to extend your undisturbed observing time. It also improves the contrast, similar to the effect of the lens shade on a camera lens, when observing during the day or when there is excessive ambient light at night, such as a neighbor's backyard security light. A slip-on metal dust cap is standard.

Dual speed 2" rack and pinion focuser: The rotating precision-made no-backlash focuser has dual-speed focusing. There are two coarse focusing knobs. The right knob also has a smaller concentric knob with a 10:1 reduction gear microfine focusing ratio. This provides exceptionally precise image control during high magnification visual observing and critical DSLR or CCD imaging. The large focus knobs have ribbed gripping surfaces so they are easy to operate, even while wearing gloves or mittens in cold weather.

The focuser drawtube has a scale marked in centimeters and 1mm increments. This lets you note individual focuser positions for easy return to the correct focus when switching between visual use and photography. Lock knobs let you adjust the tension on the drawtube to accommodate varying eyepiece/photo accessory loads, as well as firmly lock in a photographic focus. The focuser terminates in a non-marring 2" compression ring accessory holder. Two 2" draw tube extensions are included to let adjust the back focus when using a diagonal and eyepieces versus a camera.

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 go-to mounts from Celestron and iOptron, 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.

Extended lifetime warranty: This individually serial numbered Explore Scientific telescope is backed by a limited one year warranty, which will be extended to an Explore Scientific transferable Life of the Product limited warranty when its warranty card is registered with Explore Scientific within 60 days of purchase.

Tech Details

Aperture 4"
Binary and Star Cluster Observation Very Good
Focal Length 714mm
Focal Ratio f/7
Galaxy and Nebula Observation Fair
Highest Useful Magnification 204x
Lunar Observation Great
Weight 11 lbs.
Planetary Observation Very Good
Resolution 1.14 arc seconds
Telescope Type Refractor
Visual Limiting Magnitude 12.5
Warranty 1 year, extendable to lifetime


Review by:
The optics is very good for the price but the focuser needs improvement. The price is affordable enough for me to purcahse two of these scopes for my bino telescope system. (Posted on 10/24/2019)
Review by:
Crisp, clear views. relatively lightweight for many mounts. Not wild about having to use the included focuser extentions for many of my eyepieces but the views are still very exceptional (Posted on 7/22/2019)
Review by:
I bought this scope as a grab n go with my Twilight I mount. Since I rarely view planets or bright stars, I wanted to see if a triplet would be a step up in contrast from my acho refractors. For the first two weeks, I fought bad skies, but finally we had a good night just north of suburban light pollution at a star party.

I started out with the Pleides. The stars really jumped out and were pinpoint dots of light. While it had been some time that I'd got to observe with the skies we had that night, the sharpness of the stars was something I wasn't expecting.

By then M42 had gotten higher in the sky, and I turned my attention to it. The contrast and detail were immediately apparent. Typically, I view at 80x or less, but tonight I pushed the scope to just over 100x, again with impressive results.
I spent the rest of the night on these two objects, working through different eyepieces and filters.

The build was what I've come to expect with the Explore Scientific refractors. The focuser worked fine, a star test was good, and no quality issues that I can find. CA, I don't have a clue. My viewing didn't include anything that might have CA.

I was so impressed with the Essential Series 102 ED that I'm now considering replacing my AR127 with the Essential Series 127. i look forward for our eastern skies to clear so I can do a direct comparison with the 127. (Posted on 1/12/2019)
Review by:
I have looked thru a number of ES scopes both carbon fiber and Aluminum. I was really floored at the clarity these copes provide for visual. I almost bought the carbon fiber version for AP, but wanted a faster focal ratio. I have a friend that images with both the 127mm essential series and an 80mm FCD100. Both provided excellent views and images. I have been impressed with all the ES scopes, although I cant vouch for the Achromatic scopes as I haven't had access to one. If you're doing Astrophotography, at 11lbs, the OTA of the 102mm is light enough to perform well with most mounts. I own an Carbon Fiber ES 115mm f5.5 FPL-53 scope and couldn't be happier with it. Truly a Dream Scope. I only got the 115mm because I wanted the fast f5.5 focal ratio). Use the ES flattener or the Hotec Self Centering fattener if you want faster/flatter Images. Fine optics, Light weight, Great price. You wont be disappointed!! (Posted on 11/30/2018)
Review by:
Great scope. Optics give very bright and sharp views. I’m just getting into Astrophotography, but have seen the excellent results people are getting from this scope. (Posted on 11/26/2018)
Review by:
I should have gotten this telescope a long time ago it has the best resolution of any telescope I have had the pleasure of looking through. I haven't seen any defects or flaws in it anywhere. I am also using it with an AVX mount without any issues. I am looking forward to imaging with this scope. At 9.5lbs it is much easier to carry then the LX-70 M6 I used to lug around. It opens up a whole new area of astronomy for me. I am very pleased at the quality of the build and there is no CA whatsoever. I haven't had the pleasure of interacting with the ES customer support personnel, thankfully. (Posted on 10/28/2018)
Review by:
I have had the Explore Scientific ED102 for ten months. Bought it for astrophotography. Using it with a Celestron AVX mount. The optics in the ED102 are excellent. Great viewing with this scope. (Posted on 10/7/2018)
Review by:
I have owned this telescope for some time now. It is incredible for value. No noticeable defects. Well designed and engineered. It is compact and easy to walk with. Can fit in a carry on luggage with ease. Photography with this telescope is amazing. The quality is really high-end, and very sharp. Remember, this is an OTA, doesn't come with eyepieces, and no mount. Explore Scientific has great customer support too. (Posted on 10/6/2018)
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Supplied Accessories

  • Dual tube rings with Vixen-style dovetail
  • 2" dual speed rack and pinion focuser
  • Retractable dew shield
  • Dust covers
  • Finderscope base