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Explore Scientific 127ED Essential Review

Explore Scientific’s ED Essentials line promises true triplet apochromat performance at a price almost as low as most ED doublet refractors. In this review, we’ll be looking at the largest of the Essentials scopes, the 127ED.

The Essentials scopes are sold mostly for visual users or those on a budget. If you’re interested in serious deep-sky astrophotography and are willing to spend a few hundred dollars extra, the FCD100 upgrade offers (at least theoretically) Explore Scientific ED127slightly better color correction, hexagonal focusers which are more suitable for heavy cameras, and a larger unvignetted image circle, in part due to the said focuser. Visually, however, the difference is basically unnoticeable and thus most of my comments on the Essential 127ED can also apply to the FCD100 version.

Both the Essentials and FCD100 127ED are available with carbon fiber tubes. These lighten the scopes by a few pounds and avoid the expansion/contraction problems that can sometimes occur when imaging with a metal tube.

With all that in mind, let’s get to this review.

Overview of Essentials 127ED

The Essentials 127ED uses Hoya FCD1 glass, which is basically the same as Schott/Ohara’s FPL-51. This is cheaper than the FPL-53 glass widely used in most doublet and triplet apochromatic refractors today, which is also some of the most expensive optical glass money can buy.

That being said, the glass of scope is irrelevant if the optical design isn’t very good, and you should never buy a scope solely based on what glass it uses because that would be stupid. There are a lot of bad FPL-53 doublets and triplets out there that will perform much worse in controlling chromatic aberration than the Essentials 127ED. The Essentials 127ED’s long focal ratio further helps keep chromatic and other aberrations at bay.

Optically, the Essentials 127ED performs very well. The only false color you are ever going to see is a very slight fringe on bright stars like Vega, Sirius, and Arcturus, and you may have to look for it. Compared to a cheaper achromat or even a reflector, double stars require less magnification to split due to the higher contrast and sharper diffraction rings of the Essentials 127ED. View-wise the scope is about comparable to an 8” reflector, as the EMD coatings, dielectric diagonal, and lack of a central obstruction give it higher contrast and light throughput.

The focuser on the Essentials 127ED is a fairly inexpensive but well-made dual-speed Crayford. If you aren’t happy with it, it’s not difficult to swap it out for a Moonlite, Feathertouch, or other aftermarket unit, which while expensive pale in comparison to the cost of the Essentials 127ED by the time it is mounted and accessorized.

The Essentials 127ED’s lens cell is collimatable, though collimating any refractor is an especially terrifying process and you will hopefully not have to do it.

The scope comes with Explore Scientific’s standard finder shoe, which locks onto your finderscope with two nylon thumbscrews. While it is a superior design to the standard Vixen/Synta shoes, it prevents you from using other brands of finders (besides Meade and Bresser) without an awkward-looking and tall adapter or removing the shoe (which requires removing the focuser and being very careful not to drop any hardware on the objective lens).


The diagonal supplied with all Explore Scientific apochromats is a 2” dielectric mirror unit with a carbon fiber body. It is easily one of the best diagonals on the market today. The Essentials 127ED also comes with two extension tubes to use to reach focus with the diagonal and an eyepiece.

Unlike many scopes, the 127ED has a handle attached to the tube rings, which is helpful considering the scope’s 18-lb (8.16 kg) weight. The tube rings are attached to a standard Vixen-style dovetail.

The Essentials 127ED used to come supplied with a case, however, this is now no longer available from Explore Scientific – though cases for the ED80 and ED102 are available.

If you are looking to buy this scope for visual use and don’t already have a set of eyepieces, a 30-40mm 2” wide-angle eyepiece, ~24mm wide-angle eyepiece, and eyepieces in the 6, 9, and 15mm focal length ranges are probably the minimum I would recommend. Explore Scientific is one of the best and most well-known eyepiece manufacturers out there and they offer eyepieces at virtually every focal length, apparent field of view, and price.


A heavy apochromatic triplet like the Essentials 127ED needs a good mount. Explore Scientific offers absolutely nothing in the way of mounting suggestions, so some users often buy rather lightweight mounts or even ones that are plain incapable of holding the scope.

For visual use, if you want something that’s plain, simple, fast to set up, and easy to use, you might want an all-manual alt-azimuth mount.  Explore Scientific’s own Twilight II will work well to hold the 127ED and has two saddles so you could put another scope side by side with it, but it has no slow motion controls. Vixen’s StarGuy could theoretically just barely do the job, but in practice it’s probably undersized for the Essentials 127ED. Tele-Vue’s Gibraltar will work very well, but it is very expensive.

If you’re not interested in an alt-az mount, an EQ-5 class German equatorial mount is enough to hold the scope for visual use. The Celestron Advanced VX, Orion Sirius, Meade LX85, Sky-Watcher HEQ5, iOptron CEM25p, Losmandy GM-8, and Explore Scientific’s own EXOS-2GT are all excellent choices for visual and limited astrophotography capability.

An EQ-5 class mount will, however, struggle with exposures longer than 40-60 seconds even with autoguiding, so for deep-sky astrophotography, you probably want to step it up to an EQ-6. The Orion Atlas, Sky-Watcher EQ6, and Losmandy G11 (the latter of which Explore Scientific offers with a wirelessly-controlled deluxe GoTo system). Keep in mind that for any of these you will need to buy a Losmandy-style dovetail and bolt it to the tube rings, or buy a Losmandy to Vixen adapter for your mount.


In addition to an EQ6 mount like I just discussed, for serious deep-sky astrophotography with the Essentials 127ED you will also need an autoguiding setup. Mounting a guide scope will require replacing the ES/Meade shoe for a Synta-style one, or removing the tube carry handle and putting a dovetail on top of it. A 30mm or 50mm guide scope will be more than adequate for guiding with a planetary/guide camera.

A field flattener is recommended for good astrophotos that don’t look like you’re flying towards them at warp speed. Explore Scientific sells one, but it does require some figuring out of the back focus needed for a DSLR or CCD camera as little information is provided by ES to determine this factor. Explore Scientific doesn’t sell a reducer for the Essentials 127ED, so you’re stuck at the native f/7.5.


If you are a beginner in the hobby, the high price and the a-la-carte nature of the Essentials 127ED may scare you – even the most inexpensive accoutrements will probably result in you having spent $2000 or even $2500 on the scope, and an imaging setup maybe north of $3500. But the investment is worth it, whether for visual or astrophotography. For visual, you’ll have pinpoint stars, near-perfect color control, excellent contrast, and jet-black backgrounds that provide images comparable to an 8” Dob. For astrophotography, the Essentials 127ED provides tack-sharp stars with a field flattener and a good all-around focal length.

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