Orion’s ShortTube 80 Variants
Orion sells the ST80 in several variations: an OTA only with no accessories, three different Guidescope packages, an ST80-A astronomical telescope, an ST80-T terrestrial spotting scope, an EQ-mounted version, and an altitude-azimuth mounted option. Of these, only the ST80-EQ and the VersaGo GX 80ST have mounts included in the package.
The ST80-A, which is the variant I have, comes with a set of tube-rings, a vixen dovetail mounting plate for standard telescope mounts, a 90-degree star diagonal mirror, and 25mm and 10mm Plossl eyepieces. It also has a big 8×40 finderscope. Frankly, it’s way too big. A smaller 6×30 finder would have worked better, and wouldn’t have unbalanced the EQ mount as badly. I replaced the 8×40 finder with a cheap red dot finder, and found that it’s much more usable. (I find that finderscopes are usually so far back that they get in the way when I’m trying to look through the eyepiece, while a red dot finder’s view window is farther forward.)
The ST80-T is the terrestrial variant, essentially a spotting scope. It has the same eyepieces, but a 6×26 correct-image finder replaces the oversized 8×40 upside-down-image finder of the -A. The 45-degree erecting prism provides a correct-image through the telescope, but these cheap prism diagonals tend to be pretty soft and prone to adding their own additional false color, so it should only be used for terrestrial use at low-medium power. If you get one of these, you’ll want an upgraded star diagonal.
The ST80-EQ is an ST80-A on an EQ-1 type German Equatorial Mount. The EQ-1 is pretty undersized. For an ultra-portable equatorial-mounted option it might be just about adequate, but these small EQ-1 mounts are really not very good. They tend to be wobbly; they don’t stay where you leave them, and their tripods are somewhat shaky too. For wide-field viewing, this might not get in the way too badly. But then, why do you even need an equatorial mount? For a beginner, an equatorial mount can be difficult to understand and hard to use, requiring a special polar alignment procedure with every use.
The VersaGo GX 80ST is a newcomer. It came out while I was testing the ST80 (May 2021), so I haven’t had a chance to use one yet. The idea is to have a scope that can be used for both astronomy and terrestrial viewing. It has a compact single-arm mount that, unlike a typical photo tripod, is balanced even when viewing at a high angle. The VersaGo GX branded mount is a new, unique design not found on other telescopes on the market. Orion assures me it’s made out of aluminum, not plastic, which instills me with some confidence. Assuming the mount head is good, it seems like this scope option could be a good choice–compact, lightweight, scaled well to match the ST80, and even including slow motion knobs. But they’re so new, I haven’t seen any reference online to the quality of these, so at the moment they’re still an unknown. The VersaGo version comes with two interchangeable diagonals (a sharp astronomical mirror diagonal and a terrestrial 45-degree correct-image prism) and a correct-image straight-thru finderscope.
The ST80-A and ST80-T come without mounts of their own, so you’ll have to figure out one yourself. The simplest option is a photo tripod, and you might already own a suitable one. It should have a payload capacity of at least 10 lbs (close to double the weight of the scope + accessories).
The trouble is the tripod head. A traditional altaz (pan and tilt) head will work for terrestrial use when you’re pointed near the horizon, but when pointing above about 30–45 degrees, the telescope becomes unbalanced, and you have to lock down the altitude axis or else it will fall upward.
The solution is to use a three-axis head. I set the altitude axis to 90 degrees straight up. Then the intermediate axis becomes the new altitude axis, and the telescope rotates in altitude around its center of gravity.
A better solution is to use a dedicated astronomy mount. However, these can be expensive enough to come close to doubling the price of the telescope, or worse. The Explore Scientific Twilight Nano is a lightweight mount that is popular with ST80 users. An altaz mount for a telescope generally puts the altitude axis through the center of gravity of the telescope, instead of significantly below it, as in a typical photo tripod, allowing it to remain balanced even when pointing high up. Higher end ones have slow motion knobs which allow for small tweaks to the aiming, or for tracking at high power. My Vixen Porta II mount is a little overkill for the small ST80, but it is much sturdier and smoother than a photo tripod.
German equatorial mounts can be used, but they tend to be much bulkier than altaz mounts and are harder to use. The EQ-1 and EQ-2 mounts common in beginner telescopes aren’t usually suitable for serious use due to their wobble, but they are nearly adequate for a lightweight short-focus telescope like the ST80. I found that the Explore Scientific Exos Nano EQ3 mount was a good fit for size and weight, and it’s a nice smooth mount. However, I hated it with the ST80–it’s a little too big for a portable grab-n-go telescope, and the ergonomic frustrations of using an equatorial mount outweighed the meager benefits of tracking. When I had the ST80 on an EQ mount only, I almost never used it. With a solid go-to EQ mount, you could do some astrophotography with the ST80, but it’s not really for that.
My ST80 mostly gets used on a Bogen 3001 tripod with a 3030 three-axis head.
Optics of ShortTube 80
The ShortTube 80 is an 80mm aperture, 400mm focal length (f/5) achromatic refractor. It has a two-piece front lens that corrects for a fair degree of false-color-fringing (chromatic aberration). However, with such a short focal length, there’s still plenty of false color to be found at high power. Bright objects have a blue-violet halo around them.
Stars snap into focus at 80x-160x, though due to the blue fringe, there is sometimes a little ambiguity over the correct best-focus point on extended objects. (By sacrificing some focus accuracy, you can minimize the blue fringe and make it look slightly better at first glance. But try not to do that, because the in-focus white light is much more important.)
My star test indicates that my ST80 had spherical aberration (an error in the curve of the glass) on the order of 1/4th of a wavelength of light. This is an almost imperceptible error unless you go looking for it with sensitive star tests, since in practice the chromatic aberration is a more significant problem. For a short-focus achromat, it has some nice optics! The ST80’s niche as a wide-field refractor need not prevent it from working at high powers.
If you got an ST80 right out of the box, however, you might find that its images aren’t as good as they ought to be. The lens cell is just a couple of pieces of plastic. The front screws on to hold the glass steady. However, the front piece was screwed on much too tight, and as a result, it pinches the glass. You might not think a little bit of pressure would be a problem, but you’re only allowed to bend by 1/1000th the width of saran wrap—any pinching should be avoided. Thankfully, this is an easy fix. Simply take the dew shield off, and unscrew the lens cap slightly so that it is not extremely tight. The lenses should just barely rattle around if you shake the scope next to your ear. Too much rattle would mean the scope can’t hold collimation (optical alignment), and no rattle at all means it’s being pinched. Almost every plastic-lens-cell refractor I have tried this on has improved its images somewhat substantially.
The lens cell is not collimatable, and at no point has mine been in a state of good collimation. It’s not horrible, but I do suspect I’d get somewhat better images (including less noticeable false color) if I did collimate it. Collimation can be done, and there are guides online which can describe the process better than I can in the format of this review.
Subjectively, I have been very pleasantly surprised by the optics. Despite the theoretical flaws, I enjoy this scope a lot at low and high powers. It takes 160x just fine, and with collimation I bet I could go even farther. Images were bright and contrasty and actually managed to beat a 4” (100mm) SkyScanner Newtonian when compared side by side.
The Orion ST80 has a fine optic, but its mechanical design is best described as adequate. This makes it a real tinkerer’s scope–one of the main reasons so many serious observers have these things. There are so many things you can do to bring it from “adequate” to “very good.”
As discussed, the lens cell is not collimatable–it’s just two pieces of plastic. For the wide-field niche it occupies, it doesn’t really need to be collimated, and the collimation is adequate coming out of the factory, but to get it good you will have to put some effort in. There are a few methods. You can use the screws that mount the focuser to the tube to subtly adjust the tilt of the entire focuser assembly. You could unscrew the objective cell and tap the lenses into place, hoping they settle in a better state. You can check for collimation using a simple star test. As you focus or unfocus the telescope, check to see if the diffraction rings are concentric, or if they are offset as you move towards the center.
The ST80 has an all-metal 1.25” rack & pinion focuser, which works just fine. I don’t notice any flex in the drawtube, and the focuser motion is smooth enough that objects snap to focus. There is a tiny piece of a screw inside the drawtube that infringes upon the light path, which produces an almost unnoticeable diffraction spike on stars. I find the focuser to be adequate. It’s nothing special, but it works.
The inside of the OTA is painted a mediocre grayish matte black, which many observers replace with black flocking material which really deadens the stray light.
A lot of observers with ST80s modify the telescope to use a 2” focuser. GSO sells a dual-speed drop-in-replacement, but it doubles the cost and weight of the telescope, and that’s before you even add a 2” diagonal, a field flattener, and a good ultra-wide-field eyepiece to take advantage of the wide FOV. However, once you’ve made those modifications, you have a telescope with a 7 degree field of view, wider than some 7×50 binoculars and with more light gathering, but which can also be used at high powers and everywhere in between.
The False Colored Elephant In The Room
Does the chromatic aberration interfere with the views? Sometimes. I find it doesn’t really affect double stars (except for color rendition–Alberio’s color is slightly off), and even at 40x, it’s not even all that noticeable on bright bluish stars like Sirius. When observing deep sky objects, you won’t notice them at all. Surprisingly I found that even with a bright blue halo, Jupiter was still quite attractive. Saturn barely showed false color at all, as it’s considerably dimmer. The only situation where the false-color really risks spoiling the image was on the Moon, and only really when it was full or nearly full. At 100x, the contrast on the bright parts of the waxing gibbous Moon was very good, but the edge and the limb had reduced contrast due to the violet fringe.
Filters exist which can cut the false-color fringing, but block the indigo and violet light, which doesn’t come into focus (this has the side effect of tinting the image yellow). Baader sells a semi-apo filter and a fringe-killer filter. A yellowish filter will work, in fact, I’ve found that a cheap Moon Filter (the kind with a plastic casing and a slightly greenish tint) actually works pretty well to salvage views of the Moon. It could also work on Jupiter, but it’d get pretty dim.
As a daytime scope, the ST80 provides pleasing views, but I mainly use mine for astronomy. There is some noticeable false color (most notably in the tree-leaf/sky boundary) at over 66x, but at 40x with the included eyepieces, it’s not all that noticeable.
False color can also be prevented by using the included sub-aperture two-piece dust cap, which stops the telescope down to become a 40mm f/10 achromat, which in theory should have virtually no noticeable chromatic aberration–and indeed it doesn’t! However, I find 40mm is really pretty limiting. Mostly it’s useful for daytime viewing at high powers (high for a 40mm scope; 40x-80x is mid-high for an 80mm) and for the Moon when it is bright. Given my experience with other small refractors, I wonder if a 60mm cap would have been more suitable. That would still have a little color, but not a lot, and you’d still have enough resolution to be really useful.
What can you see?
The Orion ShortTube 80 is designed for wide-field, low-power scanning. Using the included 25mm Plossl eyepiece, you are shown a rich field of stars when pointing along the Milky Way. Using a 32mm Plossl for the widest possible field at the lowest useful magnification, you’re granted a binoculars-like 4 degree field of view, or 8 full moons lined up side by side. At that point, it becomes possible to fit multiple deep-sky-objects into the same field of view. Open star clusters Messier 38 & Messier 36, and Messier 36 & Messier 37, fit into the field of view together (they don’t quite manage all three together). The ST80 allows you to observe rich star fields, including the OB associations in Orion, the star clouds in Sagittarius, and the cluster-packed regions of Cassiopeia and Cygnus.
The ST80 is most at home when the Milky Way is out. During the spring, when the Milky Way is mostly low on the horizon, I found there wasn’t a whole lot to do with it. You’re not going to go chasing down dim galaxies with the ST80, unless you’re under a dark sky and you have a lot of experience. Its primary niche is to show you rich star fields, star clusters, and a handful of nebulae.
Despite its small aperture, though, I was very surprised by some of the objects I could see from my suburban skies, which not that much earlier I was struggling to see even in my 6” Dobsonian, with 4 times the light gathering aperture. This is due to, well, observing experience, for one thing, but it’s also the result of the superbly transparent optics of a refractor. I was able to see the Andromeda Galaxy M31–just the bright core, nothing fancy, but in addition to the easy satellite galaxy M32, I was able to just barely see, using averted vision and some fiddling with magnifications, the dimmer satellite galaxy M110. One of the toughest things I found was the two Messier galaxies in the Leo Triplet: M66 & M65, on a night of good transparency.
Under a dark sky, the ST80 will show you every Messier object, and the case has been made that due to its large fov, it’s a good telescope to use during a Messier Marathon (observing each Messier object in a single night).
The ST80 will also show you lots of planetary nebulae. The Blue Snowball isn’t blue in the ST80, the way it is in larger apertures, but it was obviously nonstellar and slightly hollowed out. The Clown Face nebula is a pleasant sight–it looks like a wide double star at low powers, but high powers reveal that one of the two stars is a fuzzy ball. Messier 57, the Ring Nebula, was a tiny dot at low power, discernible only from the field stars by how it behaves with averted vision vs. direct vision. At high/medium power, however, it showed a disk and was slightly hollow.
The ST80 shows magnificent views of the Double Cluster in Perseus, the open clusters in Auriga and Gemini, and the Orion Nebula looks pretty good, too, though you mostly just see the bright “boxy” inner part of the nebula.
The ST80 will also show globular clusters. At 57x, I could suspect granularity in M13 and M5, with one or two individual stars in M5. Other open clusters reveal their brightness distribution and broad structure well, but the ST80 doesn’t have the light grasp to really show individual stars. Slewing the ST80 with a quick motion, you can get several globs one after the other, and compare them easily.
A nebula filter such as an O-III or UHC filter is useful when observing nebulae. You really want it if you’re going to try to chase down the Veil supernova remnant, or to get the most out of the Orion Nebula, or to pull out extra details from the Ring Nebula and other planetary nebulae. These filters aren’t miracle workers, but they do make these emissive objects a little easier to see by blocking the skyglow while leaving the nebula’s light mostly intact.
Most of the work you’ll be doing with the ST80 will be at low and medium powers. The 25mm and 10mm Plossls included suffice for this, with the 40x being really more of a mid-range magnification than high power. However, what surprised me most was that, despite the false color fringing, this thing can work at high resolution, too. I used 6mm and 7mm eyepieces with and without a 2.5x Barlow for viewing Jupiter & Saturn, and they look great. The Cassini division is tough, but it can be seen under good conditions with high powers. Jupiter’s cloud banding reveals more than the typical two bands–perhaps 3 or 4, with hints of more subtle detail. The Great Red Spot is a subtle dark gray-brown dot. And of course, all of Jupiter’s moons are visible, as well as Saturn’s moon Titan.
The Moon is pretty good, though the aforementioned false color can be a problem in certain situations. You can sort of learn to look past it. When the blue fringe is filtered out, it goes from pretty good to great. At 100x, you can see the rille behind the ultra-reflective lunar crater Aristarchus, and the double-crater Messier reveals both shaded detail within during the crescent phases and the subtle comet-shaped ejecta pattern during the brighter phases.