Unistellar return with a sequel to the original eVscope

The eVscope 2 looks identical to the eVscope 1, even down to the silver tube and charcoal grey livery of its predecessor. It doesn’t even have an ‘eVscope 2’ label on the side! Image: Ade Ashford.

Headquartered in the sun-drenched Mediterranean coastal city of Marseille in southern France, Unistellar manufactures technologically advanced telescopes that eschew conventional optical designs in favour of a hybrid opto-electronic approach: one ‘sees’ what the eVscope is looking at, either through a high-quality miniature OLED (organic LED) screen masquerading as an eyepiece on the side of the instrument, or on the screen of a Wi-Fi connected smartphone or tablet that doubles as the eVscope’s hand controller.

The eVscope’s new Nikon electronic eyepiece with OLED display. Image: Ade Ashford.

Furthermore, each ‘Enhanced Vision’ eVscope is entirely selfcontained and eminently portable (a custom-made backpack is an optional extra), possessing a built-in image-processing computer and a self-aligning tracking mount plus tripod, all powered by an internal rechargeable battery that can operate the instrument for an entire night of observations. Despite a symphony of technological wizardry required to make it all work, Unistellar’s clever software ensures that an eVscope is both powerful and incredibly easy to use – which is a neat trick to pull off.

Each eVscope user is also invited to become part of a thriving online community of ‘citizen scientists’ encouraged to participate in wide-ranging observations of asteroid occultations, exoplanet transits, near-Earth asteroids, cometary activity and more. One could say that the eVscope exists to make science fun, designed from the ground up to appeal to those who one minute wish to capture images of deep-sky objects and then share them over social media, and the next minute to be gathering data in observing programmes that benefit professional astronomers.

A piece of foam placed between the mount and the base of the telescope tube protects the eVscope while it is being transported. Image: Ade Ashford.

The original eVscope’s public debut occurred at the Las Vegas Consumer Electronics Show in 2017. Although the introductory model has since been discontinued, Unistellar currently has two other models in production: the ‘budget’ eQuinox and the eVscope 2. Since all eVscopes operate in a very similar fashion and use the exact same control software, this appraisal focuses on the eVscope 2’s new hardware and features. For a detailed look at the operation and performance of former Unistellar models, see my reviews in the August 2020 and September 2021 issues of Astronomy Now (you can also find them online at astronomynow.com).

New features

Unistellar’s latest product looks identical to the eVscope 1 at first glance, even down to the silver tube and charcoal grey livery of its predecessor. It doesn’t even have an ‘eVscope 2’ label on the side! The eVscope 2 also features the same 11-centimetre diameter, 45-centimetre focal length (f/4) parabolic mirror of former models, so don’t expect an instrument of larger aperture or alternate focal length.

The eVscope 2 with its tripod legs extended. Alas, the tripod is bespoke to the various eVscope models – you can’t use a regular tripod with it. Image: Ade Ashford.

There are, however, two significant differences to the eVscope 2. First is a new, larger electronic sensor that lies at the instrument’s focus: a Sony IMX347LQR CMOS chip with an effective array of 2,712 × 1,538 pixels, each 2.9 microns (0.0029mm) in size. Compare this with the Sony IMX224 sensor used by both the eVscope 1 and eQuinox, and which possesses a matrix of 1,304 × 976 pixels, each 3.75 microns (0.00375mm) in size.

Hence the eVscope 2’s sensor measures a fraction more than 9mm across the diagonal compared to to the 6.1mm diagonal of the other Unistellar models. Given the identical focal-length optics of all the instruments across the range, this means that the eVscope 2’s maximum field of view exceeds that of its predecessors by 47 per cent – at least in theory. Furthermore, the smaller pixels of the IMX347 sensor means that the eVscope 2 has a finer resolution of approximately 1.3 arcseconds compared to the 1.7 arcseconds of former and current models. I’ll return to actual measurements of the instrument’s field of view and resolution later.

A look at the backend of the eVscope 2 showing the focusing wheel and collimation adjusters. Image: Ade Ashford

The second significant difference between the eVscope 2 and its predecessor is the new and improved eyepiece on the side of the instrument developed in partnership with Nikon. As with the eVscope 1, the electronic eyepiece is essentially a loupe with a premium quality miniature OLED screen at its focus. However, the optics of the eVscope 2’s eyepiece are multi-coated and an improved design to that supplied with the debut model.

First impressions

Like its predecessors, the eVscope 2 and its computerised alt-azimuth mount is an integral unit with a separate three-section tripod; the latter is unique and common to all Unistellar models – you can’t use an alternate tripod. You also receive a box of accessories containing a charger with interchangeable travel plugs, a toolkit, plus both quick start and technical guides. If you bought the optional backpack, the instrument is delivered inside it.

The eVscope 2 includes a removable cylindrical foam wedge inserted between the base of the optical tube and the mount during transportation. Without any carrying handles, one’s inclined to grasp the front of the instrument when removing it from the backpack or the close-fitting foam of its box – aleverage that places great strain on the clutch-less altitude-axis gearing, unless there is something to support it. Perhaps Unistellar received too many returns of former models with overstrained altitude drives.

Assembly and set-up is simplicity itself: open, extend and clamp the legs of the photo-style tripod to the required height, level the tripod head using its built-in bubble, then slide the mount into position and secure it by two thumbwheels. You receive two spare thumbwheels should you lose any while away from home, which is a nice touch, but perhaps they should be captive. The eVscope 2 has a mass of nine kilograms fully assembled, so you can easily pick it up and move it around to access a better view of the sky.

You need a recent Android or Apple smartphone or tablet running the free downloadable Unstellar app to operate the instrument. In common with former eVscope models, the only physical control on the mount is a lozenge-shaped power button in the fork arm. On the underside of the fork is where you find a USB-C port for charging the internal battery. There is also a USB-A port that you can use to recharge your smartphone or tablet.

Like former Unistellar models, the eVscope 2’s optical tube and computerised mount form an integral unit. Image: Ade Ashford.

The Unistellar app

Every eVscope generates a unique, password-less Wi-Fi hotspot for wireless communication between your smartphone/tablet and the Unistellar app. While you can operate the eVscope 2 from a distance of a few metres, for reliability and responsiveness you’ll get a better experience standing close by. At the time of writing, the current version of the Unistellar app is v1.6 for iOS and Android. The app also automatically updates the telescope’s on board computer firmware, if required. I used the app on an iPhone 6S+ (iOS 15.5) and an Android 7 smartphone – both considered rather old tech – without any issues.

The Unistellar app’s home screen opens with the Live-View stream from the connected eVscope, initially setting automatic limits on gain (think ISO setting on a digital camera) and exposure time (from one millisecond to four seconds). However, the app has a manual mode where you can manipulate gain and exposure sliders while observing the Moon, a bright planet, or a double star, to enhance the view somewhat if it’s under- or over-exposed.

As you’d expect, the Unistellar v1.6 app incorporates the easy-to-use Autonomous Field Detection (AFD) alignment and tracking system of former eVscope models, as well as the showcase Enhanced Vision (EV) light accumulation feature for miraculously enhancing the views of deep-sky objects in mere minutes. Both processes are actuated by single button presses on the app’s home screen.

The eVscope 2’s view of the sky is mirrored to the electronic eyepiece as well as in the Unistellar apps of up to ten devices wirelessly connected to the instrument. However, whereas one can pan and zoom around the image in the Unistellar app using conventional pinch, spread and swiping gestures, the eyepiece still only zooms from the centre of the field of view.

I disassembled the review instrument to discover that it’s powered by a 1.4GHz 64-bit quad-core Raspberry Pi 3 Model B+ with 1GB SDRAM running Linux (the eVscope 1 used a Raspberry Pi 3 Model A+ with 512MB of working memory). Apart, then, from a marginally improved RPi 3 single-board computer, a larger imaging sensor and the Nikon-designed eyepiece, the internal hardware of the eVscope 2 otherwise appears identical to its predecessors.

Down the telescope’s tube, to the Sony IMX347LQR CMOS sensor, which has an effective array of 2,712 × 1,538 pixels, each 2.9 microns in size. Imaged: Ade Ashford.

Electronic eyepiece

The Nikon eyepiece is also focusable via a small wheel on the side, so you can make precise dioptre adjustments to suit your vision. There is also improved eye relief for spectacle wearers and fewer optical aberrations. Compared to the eyepiece of the introductory model, the sky background of the eVscope 2 is a velvet black without the occasional hot pixel speckles of its predecessor’s OLED screen. Furthermore, the new Nikon eyepiece’s screen displays richer and more faithful colours. For instance, I noticed that the yellow–orange colour of red giants in globular clusters appeared richer in the eVscope 2 eyepiece compared to that of the eVscope 1 and their on-screen appearance in the Unistellar app. Subtle detail and hues in the annulus of the Ring Nebula, M57, and other prominent planetary nebulae were also easier to detect in the eVscope 2 eyepiece.

The IMX347 sensor

When I first read that Unistellar had opted for a Sony IMX347 sensor for the eVscope 2, I did wonder why they chose a CMOS detector not used by any of the big name astronomical camera manufacturers such as ZWO and QHY. I suppose that I was hoping for something like the IMX385 – the highly regarded larger sibling of the IMX224 used in former eVscopes – or an IMX178, but perhaps there were supply or budgetary factors at play. Maybe Unistellar’s optical engineers felt that their design’s 11-centimetre, f/4 parabolic mirror borders on requiring coma-correcting optics to improve edge-of-field performance anyway.

The Bahtinov mask to aid the electronic focusing. Image: Ade Ashford.

So the Ring Nebula, M57, came under closer scrutiny when I attempted to compare Enhanced Vision images of three minutes duration acquired under similar sky conditions with both the eQuinox and eVscope 2. While published data suggests that the Sony IMX347 sensor has a lower signal-to-noise ratio than the Sony IMX224 of former eVscopes, the resulting performance in terms of limiting stellar magnitude appears very similar across the models. My empirical methods agree closely with Unistellar’s published figures of a limiting stellar magnitude of +18 under exceptionally dark skies, or a couple of magnitudes brighter in average conditions, across the product range.

Super-resolution images

Since the release of Unistellar app v1.3, all eVscope models have taken advantage of built-in software with super-resolution image-enhancement algorithms similar to those that terrestrial photographers using Olympus, Panasonic or Sony DSLRs (among others) may already be familiar with, namely as ‘pixel shift’. Unistellar’s implementation works by upscaling (also known as resampling) each image before stacking several minutely displaced examples of the same star field, enabling higher-resolution recording because the overlapping diffraction effects of fine detail can be registered at sub-pixel precision.

The eVscope 2’s Sony IMX347 sensor delivers a 2,048 × 1,536 resolution in Live View mode, which is stacked and internally upscaled to 3,200 × 2,400 resolution in full-frame Enhanced Vision mode. If one choses to save Enhanced Vision images with an information overlay, they are output at 2,800 × 2,800 resolution.

Plate-solving a number of full-frame eVscope 2 images revealed a true field of view of 45.3 × 34.0 arcminutes (0.76 × 0.57 degrees), or a diagonal measurement of 56.6 arcminutes (0.94 degrees). Given the resampled image size, this implies an upsampled resolution of 0.85 arcseconds per pixel, or an actual resolution of 1.33 arcseconds per pixel. The latter agrees perfectly with Unistellar’s published specification.

Before you get too excited about a sub-arcsecond upsampled resolution for lunar or planetary imaging, note that Live-View captures of Solar System objects will be at the native 1.33-arcsecond resolution of the IMX347 sensor at the focus of the eVscope 2’s 450mm focal-length mirror. As with all the instrument’s in the eVscope range, the superresolution algorithms only work for deep-sky images captured in Enhanced Vision mode.

Concluding thoughts

The eVscope 2 has a virtually identical internal specification to former eVscope models except for the addition of a relatively inexpensive, larger and higher-resolution sensor that enables you to fully encompass the full Moon that you couldn’t do before.There is also the Nikon-designed electronic eyepiece that is a marked improvement on the eyepiece supplied with the ‘classic’ eVscope 1.

The eVscope 2’s IMX347 sensor may be bigger, but the tried-and-tested IMX224 chip of former eVscope models may still have the edge on image quality. Even the eVscope 2’s resolution advantage is marginal under average seeing conditions. Hence I feel that the eVscope 2 is an incremental upgrade at best – certainly not a product that deserves a v2.0 designation or the eye-watering £3,999 price tag (£4,199 with the backpack included).

Every eVscope is a formidable deep-sky imaging and collaborative citizen science tool, but I hoped that Unistellar were going to improve the eVscope 2’s lunar and planetary imaging prowess – perhaps by the superimposition of some form of internal Barlow lens into the imaging train when required. A second-hand eVscope 1 (if you can source one) running the latest Unistellar v1.6 app and firmware delivers similar deep-sky performance.

At a glance

Aperture: 110mm (measured)

Focal length: 450mm

Field of view: 45.3’ × 34.0’

Optical magnification: 50×

Digital magnification: up to 400×

Resolving power: 1.33 arcseconds

Limiting magnitude: +17.7

Imaging sensor: Sony IMX347

Data storage: 64GB

Weight: 9kg (including tripod)

Price: £3,999 (£4,199 with backpack)

Available from: unistellaroptics.com

Ade Ashford has travelled the globe writing about astronomy and telescopes, serving on the staff of astronomy magazines on both sides of the Atlantic.