If you’re into astrophotography, chances are that a short focal length apochromatic refractor is on your “to buy” list if you don’t already own one. There are prized instruments for their elimination of chromatic aberration and high contrast, true colour images and the tool of choice for many astrophotographers. The problem the “common folk” face with apo refractors is they tend to be quite pricey for even small apertures. While there are several small aperture apochromatic telescopes available at comparable prices, they often significantly fall short in one department or another.

The Explore Scientific Essential Series ED80 (model # ES-ED0806-01) delivers the goods with solid construction and great optics. It has a few shortcomings and compromises that keep its price affordable, but overall, this fine instrument will fulfil the needs of the most demanding photographer without breaking the bank in the process.

About the ES ED80

Specifications

On paper, this looks like a great telescope that delivers all that’s required for both visual and photographic use. Its specs are quite impressive.

Description	ED80mm Essential Series Aluminum Air-Spaced Triplet Refractor
Focal Length	480mm
Focal Ratio	f/6
Limiting Magnitude	12
Resolution	1.45 arcsec
Tube Length (Dew Shield Extended)	475mm
Tube Length (Dew Shield Retracted)	381mm
Diameter	85mm
Weight	3.4kg
Dovetail	Vixen
Focuser	2-speed Crayford-style (10:1 fine focusing)
Price	600 USD (about 1000 CAD)
Specs from Explore Scientific web site

In The Box

The scope comes extremely well packaged in an attractive box. You don’t get a lot in the box, but you certainly get what you need and what you get is of good quality. You get the optical tube permanently attached to its Vixen-style dovetail mounting plate, 2 x 2″ extension tubes (to reach focus, you’ll need 1 extension if using for visual use, or both with a camera attached), and a 2″ carbon fibre diagonal fitted with a 1.25″ converter. While a very basic package, it contains everything you need except an eyepiece. Chances are if you’re buying this scope, it likely isn’t your first scope and you’ll already have eyepieces.

You’ll also need to supply your own finder scope as it doesn’t come with one. Note that the mount is the Meade-style mount, so most standard dovetail finder scopes won’t fit. If you have to buy one, buy an Explore Scientific model (preferably a right angle finder) vs a Meade, as the ES finder is of significantly higher quality than anything Meade has to offer. You won’t regret it.

Construction

Overall, construction seems solid with a great finish. The metal objective lens cover fits snugly without slipping off. Everything was solid out of the box. The focuser was nice and smooth. The real star here is the diagonal. The carbon fibre construction not only looks great, but is extremely lightweight for something so large, weighing in at about the same as the 1.25″ diagonal that came with my Meade LX90. The diagonal also features compression rings rather than screws to hold your eyepieces in place, so you won’t marr your eyepieces using it.

While there’s technically nothing wrong with the scope, this is where things could have been done better and a few places where corners were cut to keep the price low. None of these will impact the user significantly, but they do need to be pointed out.

The “foot” Vixen dovetail mount is attached to the scope via a pair of hex bolts and a small riser block. The spacing between the dovetail and tube is too small. This results in not being able to push the scope far enough forward in my mount’s saddled to properly balance it on the declination axis once a camera is attached. Moving it as far forward as I can, it also blocks the focuser rotation (for image framing) from being able to be rotated more than a few degrees in either direction. I tried on 2 other mounts and found I had the same problem. Fortunately, I have a lightweight camera (Nikon D5100), so declination balance isn’t a big issue. But an extra 2cm of height on that riser block here would make a world of difference and allow proper balancing.

After a couple of initial uses, I found that the hex bolts that hold the dovetail plate on the scope started coming loose. I tightened them up, only to have them loosen up again after a couple more uses. It would appear there’s a slight issue here with the allowed tolerances for the threading. I easily and permanently solved this problem by putting in some semi-permanent thread lock on the bolts before re-inserting them, but I shouldn’t have had to do this.

While accurate and smooth, the focuser has a very “spongy” feel to it and is not as responsive as I’d like. While I’ve never had any real issues focusing, this spongy feel results in it taking more time to focus than is necessary. You’ll have to tweak the knob back and forth a lot to get perfect focus, as there’s a delayed response to your action, making it feel less accurate than it should. Without having the second 10:1 knob, I feel precise focusing would be nearly impossible. It’s not a show stopper, but it’s something that definitely could have been done better. Once focus is achieved and the drawtube is locked into place with the thumb screws, it holds focus accurately over an entire imaging session.

The focuser  also rotates for framing of your image. While this is a great feature on paper, its implementation is rather poor compared to other focusers that have this feature. Loosening the lock nuts causes the whole focuser assembly to wobble in the scope tube. Tolerances for the machining here are very poor. It feels very rough when you rotate it, rather than turning smoothly. And there’s a good chance that once you lock it back down in its new orientation, you’ll need to tweak the focus again. The machining for these parts doesn’t seem to be of very high precision compared to the rest of the telescope’s build. You’re much better off loosening the compression ring attaching your camera, rotating the camera and tightening it back up than you are using this feature. Keep it locked and well-seated and it’s not a problem.

None of these issues are serious or cause any real problem. These things just could have been done better.

Optics

This is one area where this scope definitely does not disappoint. For visual use, it produces bright, sharp images with potentially gigantic fields of views with long focal length eyepieces. Views of the moon are clear with great contrast and no chromatic aberration at the edges, even at advanced stages when the moon is very bright. Deep sky objects within its reach show fantastic contrast. My first view of M31 with my 40mm eyepiece was nothing short of breathtaking. It could easily resolve dust lanes, M32 and M101. It was by far the best view of M31 and its companions I’d ever seen. At higher powers, the rings of Saturn pop out. The Cassini division is clearly visible and some subtle banding is visible on the planet’s disc. Jupiter was a fine sight. The bands were clear and sharp and the Great Red Spot stood out clearly. I’m used to seeing the planets with my 8″ SCT and my older 120mm f/5 achromatic refractor. While this scope can’t resolve the finer details as well as those larger instruments can, it was still a very impressive sight considering the small aperture and short focal length. The colour and contrast produced was just unmatched by those larger scopes.

This scope really shines when it comes to photography. I’ve not have much personal experience with different apochromatic refractors, but when I see my photographic results compared to other peoples’ 80mm apo refractors, I’m always impressed by

This scope has also become a favourite for shooting the moon. Be it with a DSLR or my lunar imager (ZWO ASI120MC-S), it delivers incredible images and reveals subtle detail that only my larger 8″ SCT can come close to matching. The contrast on the fine surface details is far more pronounced on this scope, despite the higher resolution and power of the larger instrument. I can’t get the super high power views of the moon that I can get with an 8″ instrument, but the quality of the images is unquestionably superior.

One thing to note is that if you want to use this scope for photography, a coma corrector / field flattener is a must. While you may have perfect focus near the middle of your field of view, focus at the outer edges will be soft, and you’ll notice some mild comatic aberration. Most telescopes will have a curved focal plane and comatic aberration, particularly short focal length refractors.  You may be able to get by for visual use without one, but if you intend to use this scope for photography, then expect to shell out another 150 USD for the flattener. The image posted above of M81 and M82 were taken before I got my coma corrector / field flattener (it was on back order). While the image is cropped, you can see some comatic aberration in the corners and the focus isn’t as sharp at the edge of the field of view as the center compared to my other images that have a perfectly flat field and are free of all coma.

In The Field

At the time of writing, I’ve owned this telescope for almost 7 months. I’m a bit lazy when it comes to setting up my normal kit for photography, so it’s been my #1 telescope since I got it. This scope’s small size and weight make it an ideal “grab and go” scope. Its short focal length and fast ratio make it very practical to use without requiring an auto-guider, laptop, or other equipment to use effectively. I just set up on my Celestron AVX, attach my camera with an intervalometer, and after alignment, I can pull off 2-3 minute exposures without trailing. Its wide field of view is very forgiving with a DSLR attached, particularly if your camera has a full frame sensor.  It’s been a joy to use in every sense, despite it’s few minor shortcomings. It’s allowed me to capture some of the best images I’ve ever shot and without a doubt is the finest instrument I’ve ever had the pleasure of using.

Warranty

The scope comes with a full 1-year warranty from date of purchase. One very notable exception is for collimation. Collimation of such an instrument is a delicate task that’s not easily achieved. Explore Scientific offer FREE lifetime collimation service for this telescope should it ever need it. Shipping is at the owner’s expense, but they’ll do the work for free. This is a rather sweet deal!

 Pros

• Small and lightweight aluminium construction
• Easy to set up and use
• Perfect “grab and go” scope
• Fast focal ratio
• Mostly good construction
• Razor sharp optics with phenomenal colour
• Collapsable dew shield makes for a small size for transportation

Cons

• Focuser has an imprecise, “spongy” feel
• Meade finder scope mount makes attaching other finders impossible without replace the bracket
• Poor tolerances on some of the machining

Conclusion

This fine instrument delivers a lot of performance for it’s affordable price. While no apochromatic refractors of this aperture in this price range is perfect, this one is a definite step up from others brands in terms of performance. It suffers from a few non-critical shortcomings, but where it truly counts- the optics – this scope is as good as it gets for any 80mm apo refractor under $1000. You’d be hard pressed to find anything better for this price.  You won’t be disappointed

While I highly recommend this scope, I would encourage that if you can afford the extra 300 USD, the 102mm version is a much better buy and the issues I’ve pointed out with this scope aren’t present on the larger model.

If you have any questions or comments, please feel free to post them in the box down below.