Celestron’s new StarSense Explorer 203mm and 254mm devices might look like the corporate’s first foray into bigger aperture Dobsonians, however these with lengthy reminiscences will recall their StarHopper vary of the mid-to-late Nineteen Nineties out there in apertures as much as 444mm – behemoths that will nonetheless flip heads at the moment. Nonetheless, Celestron’s StarHoppers of 1 / 4 of a century in the past have been classical Dobsonians very a lot in line with the late John Dobson’s eponymous telescope design, so I ponder what he would make of the instrument reviewed right here with its radically new alignment and navigation system primarily based on a smartphone. One factor’s for certain – the StarSense Explorer 254mm is just not your father’s Dobsonian!
Meeting
The telescope is available in two double-boxed cardboard delivery containers. The biggest accommodates the pre-assembled optical tube, equipment and directions, and grosses 21 kilograms, so that you’ll want an additional pair of palms getting it indoors. The smaller field ideas the scales at 15 kilograms. The latter accommodates the instrument’s alt-azimuth mount fabricated from plastic-coated particleboard (chipboard) in flat-pack kind, so it pays to have some proficiency with Allen keys, a screwdriver and spanners (all provided as a part of the equipment). Fortunately, Celestron’s eight-page A4 fast set-up information is profusely and clearly illustrated with well-written directions, however make sure you give your self loads of ground area and put aside about an hour to place it collectively.
All sides of the particleboard parts, together with the perimeters, are confronted with the identical sturdy black plastic coating for improved water resistance. Cheaper Dobsonians usually go away bareedged particleboard hidden throughout meeting that swells over time attributable to moisture ingress from proximity to dewy grass. Particleboard is kind of dense, so the mount has strategically positioned cut-outs to save lots of weight with out compromising its energy and rigidity. These apertures double as handy hand grips along with the sturdy carrying deal with on the mount’s entrance panel.
Moderately than counting on simply three radial Teflon pads for the azimuth-bearing floor, StarSense Explorer Dobsonians characteristic a big central Teflon washer surrounding the azimuth pivot bolt that helps obtain the right stage of ‘stiction’ on this axis. Vertical slots on both facet of the mount settle for hand-knobs threaded into the round side-hubs on reverse sides of the optical tube, the hubs driving on two altitude-bearing cylinders on both sides of the mount. The optical tube merely lowers into the mount and the left-hand knob acts as a variable friction brake to regulate the altitudeaxis stiction.
First impressions
There’s no denying that the totally assembled Celestron StarSense Explorer 254mm Dobsonian is an aesthetically pleasing instrument. Its rolled metal tube in a silver-grey end stands out at midnight even when bathed in solely starlight, so that you’re not going to blunder into it on the observing subject. The 112.5cm lengthy tube has 29cm-diameter curved alloy cells at both finish, whereas the curvaceous traces of its mount, paying homage to Sky-Watcher and Orion Dobsonians, reveals their frequent Synta Know-how Company heritage. Absolutely assembled, the instrument ideas the scales at somewhat underneath 25 kilograms.
The assembled mount is 67cm excessive and the bottom is 54cm in diameter, so it’ll match by most doorways. The entrance panel of the bottom is the place you’ll discover a rack for a 50.8mm and three 31.75mm push-fit eyepieces. As for the 13 kilogram optical tube, Celestron ought to be lauded for including a stout carrying deal with on the highest at its centre of gravity. It’s a easy however very welcome characteristic that drastically aids set-up and is infinitely preferable to cradling a slippery, dew-covered Dobsonian tube near your chest on the finish of an observing session.
The mount’s altitude axis is round 58cm above the bottom, inserting the eyepiece 82cm excessive when the tube is horizontal, or 113cm excessive on the zenith. Therefore the StarSense Explorer 254mm Dobsonian is finest utilized in a seated place by most adults; I knelt on the grass most nights. The one-speed Crayford focuser is {smooth} and really exact in operation, ergonomically inclined to the horizontal for snug use. The drawtube accepts two-inch push-fit eyepieces, however you’ll want the provided extension tube and a two-inch to 1.25- inch adaptor to make use of the 25mm focal size (48× magnification) Omni Plössl supplied.
The instrument’s optics have been virtually completely aligned out of the field, however Celestron have thoughtfully supplied a small collimating cap, with detailed on-line directions discovered on their assist pages. A laser collimator confirmed that the 64mm minor-axis secondary was optimally positioned, whereas simply the merest tweak of the first mirror’s collimation hand and lock knobs have been required. The latter are recessed into the rear of the telescope, so you may conveniently stand the optical tube on its finish when not in use.
A standard red-dot finder is provided, though its place on the facet of the tube, virtually 90 levels from the focuser, is somewhat inconvenient. Nonetheless, most occasions you may be utilizing your smartphone within the StarSense dock that lies on the highest of the tube. So, with out additional ado, what’s StarSense and the way do you employ it?
A StarSense primer
Analysing star patterns in a night-sky picture captured by a digicam as a method of figuring out the place a telescope is pointing known as ‘plate fixing’. It’s a expertise that’s filtered down from skilled devices, however it was Celestron who first commercialised self-aligning expertise with their SkyProdigy vary in 2011, adopted by the StarSense AutoAlign accent as an add-on to most of their computerised telescopes two years later.
StarSense makes use of a so-called ‘Misplaced in Area Algorithm’ (LISA), very similar to that utilized by synthetic satellites to orient themselves in area, patternmatching stars in opposition to an unlimited inside database to find out the place the digicam is pointed. If the digicam’s orientation relative to the telescope can be recognized – asimple one-off alignment process – then the digicam can orientate the telescope.
What Celestron’s engineers, along with software program associate Simulation Curriculum (creator of SkySafari), have ingeniously achieved is to distil StarSense’s AutoAlign LISA algorithm, deep-sky object databases and Photo voltaic System physique modelling right into a smartphone app with a stunning graphical person interface. The app makes use of the telephone’s digicam to seize real-time star fields by way of an inclined mirror, and these are plate-solved to exactly decide the handset’s place relative to the telescope it’s mounted upon.
The StarSense Explorer smartphone app is out there for iOS and Android. Any iPhone 6 or newer is appropriate, as are smartphones operating Android 7.1.2 (or later) and manufactured after 2016. When you’re uncertain that your smartphone makes the lower, Celestron have a handy on-line checker – simply level your telephone’s net browser to starsenseexplorer.simcur.com. On the time of writing, StarSense v1.17 was out there from the Apple App Retailer, which I put in on a seven-year-old iPhone 6s Plus. The primary time you run the app, it’s worthwhile to enter a novel alphanumeric code from a card provided with the telescope. You may unlock the app on as much as 5 totally different gadgets per telescope.
Given the age of my iPhone, I used to be sceptical that its 12MP rear digicam can be delicate sufficient or have the decision (~1 arcminute) to seize sufficient stars within the app’s ‘evening mode’. Nonetheless, in exams carried out underneath a Bortle 4 sky on 10 August 2022 at 10pm BST, deep in nautical twilight with a 13-dayold Moon low within the south-southeast, I may nonetheless see stars as faint as fourthmagnitude when zoomed in on the app’s alignment display screen.
The app warns you if the Moon will intrude with star recognition, however in apply this isn’t a hindrance: no-one appears for deep-sky objects subsequent to a full Moon and also you at all times have the red-dot finder to fall again on. Observing from the agricultural fringe of a small market city, I discovered that the app may at all times plate remedy in nautical twilight and darker skies. Principally, for those who can see various faint stars it’ll work, which is most spectacular.
As soon as aligned, the app reveals the simulated evening sky in real-time primarily based on the telephone’s inside clock and its GPS-derived location. You may choose some ‘better of’ deep-sky objects from the app’s display screen, or search from a listing of the Moon and planets, shiny stars, double stars, deep-sky objects from all of the Messier, Caldwell, NGC and IC catalogues – and a few obscure ones too. It’s impressively complete, although I used to be initially disillusioned that comets and asteroids weren’t listed underneath the Photo voltaic System class, however out of curiosity I entered just a few of their official designations into the search field and most have been there. For practically each object there’s a detailed description, observing ideas and observational knowledge screens – you may even have the app discuss in regards to the object as you observe it utilizing the Celestron audio characteristic! Don’t fear that you could be be observing from some distant location and not using a cell sign or Wi-Fi as a result of the app is totally self-contained. In truth, the whole lot works even when the telephone is in airplane mode.
When you’ve chosen an object, the app captures a night-sky picture to calculate the telescope’s place, then reveals animated route arrows to the place you need to transfer the instrument to seek out it. The app routinely zooms the view as you method your goal, exhibiting fainter subject stars and extra deep-sky objects in its neighborhood. As you close to your purpose, the app requests that you just pause the telescope whereas one other plate remedy refines its pointing. By this iterative course of the on-screen reticle quickly shows corners round your concentrating on graticle exhibiting that you just’re on track, and there it’s within the eyepiece!
Celestron declare that the StarSense Explorer app has a quarter-degree pointing accuracy, and I’d wholeheartedly concur with that primarily based on real-sky testing. Offered that I had fastidiously aligned my telephone with the telescope initially of an observing session, my chosen targets have been at all times inside the subject of view of the provided 25mm (48x) eyepiece, and most occasions within the onethird diploma subject of my medium-to-high energy 7.2mm (167x) eyepiece.
StarSense dock
Each StarSense Explorer telescope possesses a dock to carry your smartphone firmly in place. Given the massive number of handsets, Celestron pulled off a neat trick devising a quick-release, onesize-fits-all adjustable holder.
Eradicating a clip-on plastic cowl from a scoopshaped lightshield on the entrance of the StarSense dock exposes a first-surface mirror that lies at 45 levels to your smartphone’s digicam. The mirror permits your smartphone to entry alignment stars excessive within the sky whereas its display screen stays at a handy viewing angle. To align your telephone entails the usage of an ingenious mechanism.
On the underside of the dock, perpendicular to your telephone, is a brief stalk with two knurled grip knobs that function two geared pinions meshing in opposition to a pair of racks and sliders at proper angles to one another. Considered use of each knobs will, to sub-millimetre precision, transfer your telephone in order that its digicam is positioned over the mirror.
Whereas it could sound difficult, the StarSense dock may be very intuitive to set-up and regulate, and the app’s user-friendly software program makes it simply as straightforward to align your telephone with the telescope as any typical optical finder. In truth, I’d argue it’s significantly simpler. Identical to an optical finder, you solely must align it as soon as after which you may neglect about it except you by accident dislodge your telephone or re-collimate your telescope.
Optical efficiency
The summer season heatwave of 2022 afforded a number of alternatives to make use of the evaluation instrument underneath clear, if considerably turbulent, skies. Nonetheless, the early hours usually delivered some tolerably good seeing during which to look at Jupiter and Saturn near opposition. The provided 48× eyepiece was too low an influence for the fuel giants, so I used my very own 7.2mm eyepiece at 167×. Saturn was magnificent, the Cassini division crisply rendered when seeing permitted. The planet’s retinue of internal moons have been additionally clearly on view, notably Tethys.
The double shadow transit of Jupiter’s moons Io and Ganymede within the small hours of 9 August 2022 made for a lovely present. The distinction within the dimension of the shadows was apparent, Ganymede clearly being the bigger moon. The tip of Io’s transit of Jupiter on 11 August shortly after 12am BST was additionally effectively noticed, the little moon trying like a shiny bead – adistinct disc – superimposed on the planet’s western limb.
Jupiter’s Nice Crimson Spot, near transiting Jupiter’s meridian on 20 August, was apparent even with the provided eyepiece at 48×. The seeing was common, however utilizing my very own 7.2mm eyepiece revealed fleeting glimpses of tremendous floor element when the view crystallised into readability. By the way, the instrument’s Dobsonian base is exceptionally secure: vibrations induced by a pointy faucet on the tube die away in a second.
A 254mm-aperture telescope gathers enough gentle to disclose a fantastic many deep-sky objects in appreciable element underneath darkish, moonless skies, and I by no means discovered the StarSense Explorer Dobsonian wanting on this regard. From my lightpolluted observing website I may maintain Messier 13 even underneath direct imaginative and prescient, as certainly I may the central star and core of the Cat’s Eye Nebula. The latter had a distinctly greenish tint. Messier 27 was beautiful, the diaphanous parts of the Dumbbell Nebula revealing glittering stars of the wealthy Milky Approach backdrop.
Concluding ideas
The fusion of computerised star recognition and object location with the elegant simplicity of a Dobsonian telescope might seem like the antithesis of what John Dobson was striving for, however to my thoughts it’s a wedding made in heaven. The intuitive alt-azimuth motions, stability and ‘largest bang to your buck’ in optical efficiency and aperture afforded by a Dobsonian wedded to the easy-touse, dependable and just about foolproof StarSense system is a profitable mixture.
Celestron’s 254mm StarSense Explorer Dobsonian retails for about the identical worth as competing bare-bones 300mm fashions, however the former’s intuitive and really effectively executed object location system greater than makes up for the smaller gentle grasp.
However that is principally in regards to the StarSense Explorer app and the way in which that it’ll revolutionise your observing classes. Its lovely graphical person interface (which, by the way, you may redden to protect your darkish adaption) invitations you to discover a constellation or area of sky in better element, making serendipitous finds right here and there. The way in which that it makes use of any appropriate telephone to reliably plate-solve and discover objects implies that you don’t want nice swathes of clear sky to hunt out alignment stars, as is demanded by conventional computerised GoTo mounts – certainly, it successfully renders such strategies out of date. Make no mistake, the StarSense Explorer app is a recreation changer that can enchantment to seasoned observers and smartphone-addicted millennials alike.
I felt a definite pang of remorse when the courier arrived to take it again to First Gentle Optics; I miss it already.
At a look
Optical design: Newtonian reflector
Aperture: 254mm
Focal size: 1,200mm
Focal ratio: f/4.72
Focuser: Single-speed Crayford, 50.8mm with 31.75mm adaptor
Mount: Dobsonian with variable friction brake (altitude axis)
Object location: StarSense Explorer app (person provided telephone); crimson dot finder
Eyepiece: 25mm Omni Plössl (48×)
Equipment: StarSense Explorer dock, eyepiece rack, collimation cap, carry handles for OTA and base, pointing knob, mud covers
Tube size: 112.5cm
Tube weight: 13.25kg
Base weight: 11.6kg
Value: £849
Particulars: firstlightoptics.com
