The Astro-Video Systems DSO-1 camera is sensitive and versatile, capable of imaging the Moon and planets one minute and deep-sky objects the next. It is also small and light, weighing just 140g, so it will not overtax even the smallest telescope mount. The DSO-1 is shown with the optional 1.25-inch focuser adaptor attached and a coin for scale. AN image by Ade Ashford.

Equipped with a 1.25-inch nosepiece, the AVS DSO-1 camera can be used instead of an eyepiece. AN image by Ade Ashford.

One of the fastest growing and innovative companies in this sector is Florida-based Astro-Video Systems (AVS), the brainchild of astronomer and electronics guru Matt Todor. In common with many of us, Matt lives under heavily light-polluted skies and found the ‘instant gratification’ of astro-video very appealing. His first production model appeared in 2012 and AVS currently offers three lines of high-performance cameras, with more in development. The DSO-1 is a high-gain, low noise and long integration video camera that received a design upgrade in 2015 and is currently on sale for $109 (as of early July 2015). We chose to review the DSO-1 as it is custom modified both in hardware and firmware based on proprietary AVS work.

The 4cm by 4cm rear panel of the AVS DSO-1 camera features the On-Screen Display (OSD) multi-function menu ‘joystick’, the BNC composite video output, a 12V DC power and a hand remote connector (IRIS). The power indicator LED (PL) is thoughtfully red to help preserve dark adaption for those not looking at the computer screen. AN image by Ade Ashford.

Weighing just 140 grams (5oz) and with overall dimensions of 75mm × 45mm × 42mm, the DSO-1 is light and tiny — so small, in fact, that it could slip inside a two-inch focuser. This is a fact not lost on AVS, who have developed an ingenious adapter called the INFOCUS that makes the camera compatible with virtually all Newtonians/Dobsonians without having to re-engineer the primary cell to move the main mirror forward, as is often the case when using a visual reflector for astrophotography. (Most refractors have sufficient back focus, while catadioptrics — Schmidt– and Maksutov–Cassegrains — offer an almost infinitely variable focal plane.)

The heart of the DSO-1 is a highly sensitive Type 1/3 Sony EXview HAD CCD II sensor measuring 4.9mm x 3.6mm, offering a 976H by 582V pixel matrix (PAL version). Each pixel is 5.0 microns (H) by 6.25 microns (V), comparable in size to those used in DSLR APS-C sensors. AN image by Ade Ashford.

In common with most IVCs, the camera’s myriad features are configured on-screen via a series of hierarchical menus. These are accessed by pressing the multi-function OSD ‘joystick’ button on the back of the unit, or remotely via a cable or Bluetooth adaptor (available separately). These settings can be saved for future use even when the camera is powered off. While learning how to perform these fingertip set-up functions while watching an adjacent screen or monitor is a quick process, in practice the joystick button is fiddly to operate. Besides, remote control eliminates camera shake during configuration.

A single-shot screen grab of the Whirlpool Galaxy, Messier 51, captured with the DSO-1 at the f/2 Hyperstar focus (560mm focal length) of a Celestron C11 Schmidt–Cassegrain telescope. Much fine detail is recorded in the galaxy’s spiral arms. AN image by Ade Ashford.

A single-shot screen grab of the Dumbbell Nebula, Messier 27, captured with the DSO-1 at the f/2 Hyperstar focus (560mm focal length) of a Celestron C11 Schmidt–Cassegrain telescope. The red and green hues were obvious on the monitor. AN image by Ade Ashford.

The front of the DSO-1 camera features a standard C-mount thread, so the 1.25-inch focuser adapter can be swapped for, say, a C-mount to Canon EOS adapter if you wish to use DSLR EF-S camera lenses. AN image by Ade Ashford.

Output from the DSO-1 can be viewed on a colour television or monitor with RCA phono inputs by using the appropriate adaptors, or one may use a cheap and widely available USB 2.0 video capture device in a PC or laptop to save screenshots or video to disc. AVS sells a wide range of accessories on their website. This image shows a typical setup where the composite video cable from the camera (yellow connectors) terminates in a BNC to RCA adaptor connected to an EasyCap video capture device (the red and white sound channel inputs are not required) in the USB port of an Apple MacBook. The double red connector at the bottom is the power supply to the camera. AN image by Ade Ashford.

I only wish that I had more time to explore the lunar and planetary imaging capabilities of this fully-featured camera, but the online user galleries of the AVS Yahoo! Group eloquently testify to the DSO-1’s capabilities in this regard. I for one feel compelled to do far more deep-sky astro-video work thanks to the ease of set-up compared to astro-imaging with a DSLR, plus the ‘instant gratification’ factor of video cannot be underestimated.

Former integrating video camera users will find this camera easy and intuitive to configure and use, but even novices will be up and running in no time thanks to AVS’ excellent documentation. Video output had excellent suppression of internal noise and amp glow given that it was not particularly cold, showing that the impressive 3D digital noise reduction really does work well. The DSO-1 is supplied without filters to ensure maximum sensitivity, so you will need to invest in an infrared cut filter if you intend to use it with most refractors.

Conclusions
The AVS DSO-1 represents excellent value for money — easy to set up, great fun to use and extremely versatile. For the price of a modest eyepiece you can own a device that will show you colour deep sky objects in virtual real time from the comfort of your living room (if you have a sufficiently long cable!) in far more detail than you could possibly see visually with a telescope of twice the aperture. Or you can display the Moon and planets in crisp 700TVL horizontal resolution on a screen to groups of people simultaneously — a boon to astronomical societies or educators. The DSO-1 Video camera has multiple uses bounded only by your imagination and may bring the wow factor back to your public viewing sessions.

ED glasses are fast becoming ubiquitous in astronomical equipment, particularly in banishing the remnants of chromatic aberration of the classic refractor. Many APO (apochromatic) telescopes are small in aperture, so although the images are perfectly honed, definition and light grasp remain limited. It is nice therefore to see an affordable APO with some meat on its bones.With an aperture of 115mm (4.5″) at f/7, this ‘scope aspires to have enough glass for probing the depths, while also having the breadth to prise the light apart for resolution. Bolted on to the air-spaced triplet optics is a beefy three-inch dual-speed Crayford focuser, strong enough for precise control of even heavy visual or imaging equipment.

Measuring less than 28″ long (dew tube retracted) this is a significant but eminently portable instrument — boasting a mass of only 15.2lb.

This kit includes a Vixen-style dovetail mounting rail on two heavy duty-rings, all enclosed in its own hard carry case.

Objective lens design: air-spaced, fully multi-coated, 3-element with FK-61 extra-low dispersion (“ED”) glass
Aperture: 115mm (4.5″)
Focal length: 805mm
Focal ratio: f/7
Optical tube length: 705mm (dewshield retracted)
Optical tube weight: 15.2lb (6.9kg)
Focuser: 3″ dual-speed (11:1) Crayford
Additional included accessories: tube rings, Vixen-style dovetail, foam-lined hard carry case.

Price: £1799

For more information: scsastro.co.uk

It is a continuing (and annoying) puzzle to me why accessory manufacturers resist the commercial and affordable production of Filar micrometers for amateur astronomers. Their twin-threaded ability to easily measure the separation of stars or detail in the visual field, merely by turning a dial, has ensured my continued ownership of one — albeit a time-travelling refugee from a more enlightened (Victorian) age.

Rant over, there are never the less modern-day equivalents that use a reticuled eyepiece to achieve a result approaching that of the filamentary design. This 25mm eyepiece has a field cross-hatched by a reticule that permits measurement through sub-divided etched lines. The reticule’s illumination is adjustable via a large tactile knob — to match requirements of the object being observed.

Weighing in at only 131g it will not imbalance your ‘scope; and for the eye, a fold-down rubber eyecup means comfortable use is offered to normal or bespectacled observers.

Also usefully employed as a guiding eyepiece, the Polaris is fitted with a T-2 thread, although 1.25″ and 2″ nosepiece adapters are available.

As I have often stressed, an uncollimated telescope is no telescope at all — although it may serve as a flux collector, if fuzzy viewing is what you are into. A good telescope will have optics that have transmitting or reflecting surfaces that have been perfectly formed to within fractions of a wavelength, Their respective alignments must reach an accuracy commensurate with these proportions. Laser collimators allow this to be accomplished. The Howie Glatter Blug™ makes available improved alignment of a reflector’s primary mirror.

Blug™ is a charming contraction of ‘Barlowed collimation plug’ and it does something remarkable to the already acutely useful laser light being emitted from the collimator. After the laser beam passes through its anti-reflection negative lens, this neat little devil (placed at the base of the focuser tube), casts a returned shadow of the collimation target on its angled face, making adjustments of the primary mirror clearer and therefore more accurate.

There can be no sweeter sense of achievement than when you can see that an optical system is ‘closed’, with all elements in-line and on-axis — an achievement that is readily apparent in use, too. After all, once your responsibility of arranging the mechanics has been met, you can leave physics to do the rest.

Price:
£39 (1.25-inch model)
£69 (2-inch model)

For more information: www.firstlightoptics.com

Long ago, during a pitch black observing session at a weekend Astronomy course, I watched, amazed, as an observer abruptly disappeared. Unfortunately, this was not because the darkness itself had enfolded them, but that they had precipitously fallen into an unseen four-foot gully. Total darkness is great for astronomy, but not for seeing what you are doing or where you are going. With true irony, astronomers need to do both.

This headband flashlight enables vision with due respect to the needs of astronomy. White and dark-adaption red illumination is provided by one white and three red LEDs respectively. The forehead lights themselves are held in a 83g low-profile unit that does not protrude like some that aspire to Dalek-like proportions. There is a large power button too, for frostbitten or gloved fingers. Three AAA batteries supply up to 200 hours of energy — more than enough for many ‘torch’urous observing sessions.

Price: £34.95

For more information: www.princetontec.com www.tringastro.co.uk

Thirsting for the stars, novices in astronomy are often seeking a one-stop solution to quench these initial desires. It is generally advised that this preliminary instrumental step be made with an able and economical all-rounder. Such a telescope should not disappoint, nor impoverish, although the latter will most certainly occur once the new observer (with experience under their belt) decides on their observational needs with greater precision.

This ‘scope, aimed at the beginner, hits all the right notes. The compact Maksutov–Cassegrain design offers a manageable piece of equipment weighing only 4.85 kg (10.7 lbs) that can be easily ‘man handled’, despite an effective focal length that would otherwise require a conventional tube length of nearly one and a half metres. The optics’ aperture is a very capable 90mm, providing access to resolved planetary detail and many deep sky objects. As a GoTo, it can automatically guide the user to any one of the objects held in its 42,000 item database (so long as the object in question is above the horizon!).

Once found, the object will stay in the eyepiece field of view via the mounting’s sidereal drive — with lunar and solar tracking rates available when required.

The included eyepieces (25mm and 10mm) will supply magnifications of 50× and 125×, ably bridging the start-up requirements of both a usefully wide field and the chance to elicit finer detail.

Price: £337.86

For more information: http://uk.telescope.com/

Despite the many advantages that reflectors provide, refractors maintain advantages of their own; not least through the absence of a blob of ‘silver paint’ impinging on the centre of their primary element.

This new achromatic refractor, made in the classic Fraunhofer doublet design, boasts a very significant 152mm (six-inch) aperture. With a focal ratio of a little under f/8, the focal length of 1200mm means that powers of up to 300× can be usefully employed whilst retaining very good colour correction.

Tube furniture features an 8 × 50mm finder and Bresser’s bespoke Hex Focus system, a vignetting free 65mm diameter focuser offering no slippage or image shift, even with heavy two-inch diameter eyepieces.

A remarkably economical price for a six-inch refractor, it includes incorporated mounting rings and handle, a 26mm Plossl eyepiece, a 1.25″ diagonal and a T-adapter.

Price: £433

For more information: www.bresser.de

The acquisition of a telescope is a personal thing. Indeed, though some may deny it, we can become very attached (even fondly) to the instruments that give us such a thrill observing the Universe. It can come very hard, then, for us to question their quality. It might even seem a betrayal of friendship, that we would look into their very bowels to examine their integrity.

But before we get carried away in a wash of sentimentality, let us not lose sight of the fact that we all spend a great deal of money on observing equipment. Being able to challenge the claimed quality of our purchases is essential. Although it might be a brave observer who dares to find out if poor images are the result of optical quality, not the ‘seeing’, that knowledge is essential for assessment of the observations themselves.

A star test — the live assessment of a star’s focused and extra-focal images — is a definitive and exacting exposure of a telescope’s optical quality. But in order for it to reveal the finest details of that quality, the Earth’s turbulent atmosphere has to co-operate by providing steady untroubled air through which the light is passing. (So, little hope there!)

A Ronchi eyepiece can provide information only approaching that of a star test, but is not so dependent on atmospheric stability. The device turns a star’s light into a series of lines that demonstrate the presence of errors of form in the optics encountered in the optical train. This new version employs a chrome-on-glass grating of 10 lines per millimetre, providing a high-contrast display of starlight that enables good analysis. A manual is provided that explains what can be seen and the conclusions that may be drawn. (A photographic version is also available.)

I wonder which telescopes will view the approach of this eyepiece as a chance to shine, or shrink back with the fear of exposure?

Price: £32 (visual) £39 (photo)

For more information: www.gerdneumann.net

Almost as soon as the telescope was invented, there was an idea that additional comfort and usefulness might be gained by twining the instrument for use by both eyes. I seem to dimly recall that even Galileo suggested shipboard binocular observations in his search for tools of navigation; although his proposal for the anxious observer to observe whilst swinging wildly from a bosun’s chair was a mite ill-conceived!

7×50mm or 10×50mm binoculars are correctly purported to be a good specification for general low-power/ wide-field astronomy. But astronomy is also about leaching as much light from the sky as possible. The 70mm aperture of these binoculars has twice the light-gathering power of those using 50mm. Designed with both terrestrial and astronomical observations in mind, BaK-4 prisms and lens coatings ensure as much light as possible (85 percent) gets through to the observer. The comfortably over-sized eyepiece elements provide a generous eye relief of 20mm too. Coming in two models, the 10.5 times offers a wider field, whereas the 15 times provides a slightly darker one.

Price: £199 (both 10.5x and 15x)

For more information: www.opticalvision.co.uk

Red dot finders have been around for some time now — adopting various guises in their ongoing improvements. Yet with this new version from Celestron, there is definitely a new slant on their design.

Other ‘unitary’ red dot (x1) devices have inherently suffered from the same integral problem as their cross-haired cousins — in that the target becomes obscured just at that moment when accurate alignment is desired. Yet the Star Pointer Pro does not blot out its prey — it surrounds it!

Nested binary rings quite literally target an object as its own bullseye, effectively keeping an object in view to enable perfect alignment. That is not all — a huge 40mm optical window means that it is not necessary to keep peeping out from behind the finder to see how you are getting on whilst sweeping the sky. Its wide field of view makes it far easier to star hop in comfort.

It ‘leaps’ upon your scope via a dovetail connection and weighs just 5 ounces. An included CR2032 battery supplies an LED sufficiently bright for use in daylight.

Price: £32

For more information: www.celestron.uk.com

As an observer who cut his teeth in the days when inflicting incoming light with unnecessary optical elements was viewed with horror, I can testify that diagonals were once used only when absolutely necessary. Canvassing by professional chiropractors and later exacting technologies have changed all that.

A telescope’s optical quality is only as good as that of the poorest element in its light path. But this diagonal will not be that. This star diagonal has a surface that has been honed to ¹/₁₂^th lambda, meaning the precious wave front delivered by the telescope optics will not be impacted by the reflection. Nor will many photons be lost in the 90 degree turn, for the mirror renders a 99 percent delivery of light to the eyepiece.

Nice additional touches of quality include compression ring eyepiece clamps, 2″ to 1.25″ (31.8mm) reducer, push-fit safety undercut and four-point collimation adjustment should it be needed — the carbon fibre livery makes it look super, too.

Price: £165

For more information: www.explorescientific.co.uk

As its name suggests, this telescope’s eight inch (203mm) aperture provides a light grasp suitable for exploring the galaxies and nebulae that constitute the Messier catalogue — and many other deep sky objects besides. Yet its 1218mm focal length (f/6) gives it access to the higher magnifications required for planetary observations too.

Its classic Dobsonian (alt-az) mount immediately makes it intuitive and simple to use — yet this is an instrument that offers features above those found in other telescopes of this type.

Its claim on Messier object observations is underlined by an over-sized focuser tube that will avoid inducing the large eyepiece vignetting that a smaller barrel might incur. The mass of heavyweight eyepieces is no trouble for the ‘scope either because large altitude wheels diminish their impact on instrument’s equilibrium — and in another trick, if they do create an imbalance, the whole tube can be moved within its tube rings to compensate! So binoviewers, massive cameras, filter wheels — they’re all in a night’s work for this versatile little beast.

Speaking of versatility, the tube itself can easily be decoupled for dovetailed attachment to another mount, such as an equatorial for astro-photography.

And this eager eight inch is keen for field work too, for the rocker box has been designed to ‘flat-pack’ in seconds for easy transport to dark sites.

Price: £333

For more information: www.bresseruk.com

Embedded in the constellation of Centaurus a strange star shines. About 50 light-years away, the pulsating white dwarf BPM 37093 (V886 Centauri) is said to contain a crystalline carbon core — which we humans know by another name: diamond.

The star’s magnitude of +14.0 may make its observation challenging for many amateur telescopes, but use of its material in this focuser will at least ensure that its appearance is tack sharp.

This range of three new focusers, aimed at refractors, SCTs and Newtonians, employ real diamonds to create a micro-geared high-precision drive system. These focusers offer complete freedom from backlash and flexure, with almost fluid smoothness of motion. Yet the gentleness is tempered with strength, able to vertically hoist a focusing cargo of 6kg (13 lbs).

A 1:10 fine focus gear ensures complete control and an over-sized 55mm internal diameter prevents vignetting on large-diameter eyepieces. A ring clamp at the business end offers the facility of connecting T2, M48, M68 and other adapters for direct connection of accessories. A 2″ eyepiece clamp features a brass ring compression grip and 1.25″ eyepiece adapter.

Dare I say, this diamond focuser may be one to take a shine to!

Price: £239–£249

Supplier: Baader Planetarium

Details at: www.baader-planetarium.de

Vixen has introduced a remarkable looking 7-element ocular that yields an expansive 83° apparent field. Yet the optical somersaults entailed in doing so are achieved without harm to the final image. Components of low dispersion high transmission glasses, plus (in partnership with the usual multi-coating) a mysterious additional surface coating, yield a stellar field with sharp edge-to-edge field definition with no vignetting – even on instruments of low focal ratio.

The eyepiece optics are not the only aspect that has been thoughtfully designed – the tactile bodies too exhibit some nice touches. When they are put down, they stay put, thanks to an octagonal anti-roll barrel. They stay put in the focuser too, with an undercut sleeve designed for both locking screws and compression rings.

Currently in five focal lengths ranging from 3.5mm to 14mm.

Price: £199–£249

Supplier: First Light Optics

The Orion EON 115mm and 130mm ED triplet refractors are mean imaging machines, capable of capturing wide-field star-tossed imagery. Yet with an eye on taming those field extremity stars that can get tortured into tiny streaks of light instead of pinpricks, Orion introduce this dedicated 3″ field flattener.

One side of the field flattener threads on to the 3″ focuser, whilst the other offers a wide M48 thread that enables fixture of DSLRs, etc. without the vignetting possible with smaller M42 designs — particularly when deployed with full frame sensors.

Between the threads, a multi-coated two element corrector does its job without modifying the focal length — so image scale is not changed.

Its fully locked threaded attachment ensures no flexure as when fitted it physically becomes part of the telescope — and offers that security to the imaging accessories behind it.

Price: £329

Supplier and further details: SCS Astro

There is a delicious irony that ’finding’ the brightest astronomical object in the sky is associated with the greatest danger. Using a conventional finder will result in immediate blindness and irrevocably ruin the finder’s eyepiece too. Certainly, dazzling attempts to align the eye along the telescope tube towards the Sun also puts the vision in harm’s way and should never be considered.

Never-the-less, the Sun’s own ferocity can be turned to good use. Indeed, there always seems something traitorous to me in the nature of how solar finders work. The Sun is forced, by its own light, to cast a beam or shadow that enables an observer to direct an instrument towards it.

Using the ground shadow of the telescope itself is always problematic. The often unresolvable surface upon which that angled shadow is cast (especially if it is grassy) does not lend itself to precision. Yet this sol finder is neat, light and precise.

Consisting of two discs placed at either end of a base plate, the Sun-facing pinhole first casts its shadowed beam onto the back plate for rough alignment. As the beam strikes the centre, the Sun pierces a reddened glass target to signify the ‘scope is aligned. Simple, safe and swift.

The unit itself is designed to fit Lunt and Televue telescopes, but can also be supplied with a dovetail base for deploying on other ‘scopes.

Price: £29.99 (unit only), £39.99 (with dovetail/stalk)

Supplier: Altair Astro

Details at: www.altairastro.com

Most people drawn to astrophotography are detail-orientated and technologically savvy – particularly if they were long-time amateur astronomers before moving into astrophotography. However, those that enter astroimaging by the hobbyist photographer route can become quickly disillusioned by the associated technology (equatorial mounts and autoguiding, for example) and hanker after the simpler camera lens approach. Is there a way to simplify the astroimaging process and reduce exposure times dramatically? Celestron believed so, and this was the impetus that drove the company’s optical engineers to develop the Rowe-Ackerman Schmidt Astrograph (RASA) profiled here.

An astrograph is a telescope designed for astrophotography rather than visual use. It possesses an optical system highly corrected for optical aberrations and is typically ‘faster’ than telescopes designed for use with an eyepiece. A typical refracting astrograph may be f/6, while a reflecting design may be f/4. Recall that the focal ratio (or simply f/ratio) is the focal length of the instrument divided by the aperture of its primary lens or mirror. At f/2.2, Celestron’s RASA is clearly very fast indeed, comparable to prime DSLR lenses.

However, if we now turn the same equal aperture lenses to an extended object such as the Orion Nebula, the f/4 lens will require an exposure four times longer than the f/2 lens in order to record the same degree of whispy detail, since the same light is being spread over four times the area (but the f/4 instrument will show the Orion Nebula at twice the scale). Similarly, a f/2 lens or mirror is twice as fast as one of f/2.8, or sixteen times as fast as an f/8. Mathematically, then, photographic speed is proportional to the square of the focal ratios.

Celestron in the U.S.A. was the first company to perfect a commercial process for the mass-production of the hitherto hard-to-make Schmidt correctors, and by the early 1970s had a 5.5-inch f/1.65 Schmidt camera in production. By the middle of that decade, it added an 8-inch f/1.5 Schmidt camera and, later still, limited quantities of 14-inch Schmidt cameras. While Celestron’s Schmidt cameras of 40 years ago operated at photographic speeds way in excess of anything but the fastest lenses, they were still specialist instruments that required more than a modicum of expertise to use. Nevertheless, they revolutionised the art of imaging.

Celestron soon realised that while Fastar undoubtedly produced good images very quickly with the small CCDs available at the time, such an add-on needs to be matched to the optical system if it is to be optimised for larger sensors off-axis. The Fastar lens for the 11-inch Schmidt-Cassegrain was never put into full production, so US-based Starizona started produced their own fast corrector lens system called HyperStar for the 11-inch SCT in 2002. Starizona now produces HyperStar solutions for most Celestron SCTs from the C6 up. Great though HyperStar is – I have a HyperStar3 permanently installed on my C11 – it is an add-on that is not optimised for the optical tube it is used with.

Celestron’s Rowe-Ackermann Schmidt Astrograph (RASA) also permits you to place your CCD camera or DSLR at the focus of the instrument’s primary mirror after its light passes through a fixed, internal corrector lens assembly – but any resemblance to a HyperStar system ends here. RASA is largely the brainchild of two very talented optical designers, Dave Rowe and Mark Ackermann. Rowe studied astronomy and astrophysics at Caltech, holds 15 patents and designed and built many instruments for Celestron and PlaneWave Instruments. He also worked closely with Celestron in the development of StarSense technology. Mark Ackermann, Ph.D has published dozens of optical telescope design papers and holds six US patents related to optical systems. RASA is a patent pending design.

While it is often stated in the literature that the 11-inch RASA offers a 70 mm optimised image circle, this figure actually applies to the 14-inch model intended for science-grade, wide-angle space situational awareness activities. Even so, the commercial 11-inch RASA has a 52mm diameter useable field, meaning that enormous 36.8 x 36.8mm CCDs like the Kodak KAF-16803 may be used with it. Full-format DSLRs are therefore easily accommodated for 3.3° x 2.2° fields, so 42mm T-thread and 48 mm camera adapters are provided (55mm back focus). RASA provides 78 percent illumination at the corner of a full-frame DSLR sensor, easily compensated by flat fields. APS-C-sized sensors are essentially full illuminated across their 2.0° x 1.4° fields!

The rear cell of the RASA has the primary locking clutches as implemented on the Edge HD models to ensure that absolutely no primary mirror movement occurs while imaging. Since there is no baffle tube as found in a conventional SCT, a solid steel shaft and improved brass bearing focusing system dramatically reduces image shift. A beautifully smooth 10:1 reduction FeatherTouch micro focuser that is RoboFocus compatible ensures easy and repeatable focusing with a Bahtinov mask . Finally, a 12V Maglev cooling fan improves airflow for better cooling of the optical tube to ambient temperature, reducing thermal effects.

Like a Fastar/HyperStar system, RASA images are mirror reversed, but it is a simple matter to flip the image after digital processing. Since the CCD or DSLR must sit in the entrance pupil of the telescope, so the shutter release cable of a DSLR or the power/USB cables to a CCD camera will introduce an element of diffraction since they must cut across the light path. The secret to minimising this is not to make the cable straight where it interposes on the corrector, but to give it a gentle curve: this will ensure that the diffraction is more evenly spread around the image rather than manifesting as a ‘spike’ or flare emanating from bright stars. Since the bodies of DSLRs typically have curved edges, diffraction is not as severe as one might first suppose.

Specification
Optical design: Rowe-Ackermann Schmidt Astrograph
Aperture: 280mm
Focal length: 620mm
Focal ratio: f/2.21
Central obstruction: 114mm (41 percent of aperture diameter)
Image circle: 43.3mm Ø, 4° field
Spot size: <4.4 μm RMS across field of view
Off-axis illumination: 83 percent at 21mm off-axis
Image scale: 10.8 mm/°, 332 arcseconds/mm
Wavelength range: 400-700 nm
Optical filter: 68mm Ø
Back focus (with included adapter): 55mm
Back focus (from filter): 81mm
Tube material: aluminium
Tube dimensions: 84cm long, 32cm diameter
Tube weight: 43lbs (19.5kg)
Focuser: FeatherTouch microfocuser, coarse and fine focus
Other features: Ventilation fan, Losmandy-style D-plate mounting bars

Price: £3299.00 (SRP)

For more information: www.celestron.uk.com

What on Earth would 17th century observers make of today’s compact telescopes? There they were, struggling with ever-lengthening tubes so vastly prolonged that they required ship’s rigging to hold them fast; yet now a telescope of similar aperture, with a focal length of over a metre, can be folded into a tube barely more than a third of that.

This new grab ‘n go telescope is a modified Cassegrain bearing a 110mm primary mirror. This spherically figured mirror, in combination with the Cassegrain secondary, produces a focal length of 1035mm – making this folded system a very respectable f/9.4. It is therefore similar in ability to the ubiquitous f/10 SCT systems – apart from not having a (corrector plate) slab of glass in front to gather fresh water from our ever-drenching atmosphere.

The ‘user’ end features an integral two-port flip-mirror system – one for the observer and the other for a camera (the latter having a 42mm thread for T-ring fittings). Weighing just 4.6 lb (2.1 kg) with dovetail plate and finder, it will be no trouble at all for the average portable mount – or a well-padded backpack. With such compactness proceeding apace, how long I wonder before that backpack also contains a dehydrated up-and-over turret observatory (just add water)?

Price: £309

For more information: www.telescopehouse.com

Finders these days ‘find’ themselves branching out from their usual task of merely functioning as a tube that hones the main telescope’s gaze. They frequently possess optics sufficient to qualify them as fully fledged observational instruments in their own right. Besides working to locate targets, they offer abilities that directly assist in the various tasks that the main telescope is put to. Such is the new Orion 60mm guide scope.

Refractors of 60mm aperture are not to be sniffed at – in themselves, historically, having made discoveries of great merit. Capable of use with optional 1.25-inch eyepieces, this smart-looking telescope can therefore be utilised as a telescope in its own right – offering the abilities of a good achromatic refractor that can also be used for imaging.

Never forget that although diminutive compared to big reflectors or SCTs, a 60mm refractor is still capable of tunnelling down to magnitude 11.5 – and this f/4 version has a 240mm focal length that makes it capable of a very useful range of magnifications, beginning at a wide-field 9× with a 25mm eyepiece.

As a finder, this new model has been designed by Orion for use with their StarShoot AutoGuider (& Pro) – with a fine movement helical focuser that does not rotate. The fixed orientation and zero-shift of the focuser means that potential guide stars do not jiggle or move during the exercise of fine focus – easing this occasionally fretful task.

The helical thread allows 10mm of fine adjustment, while if necessary the drawtube provides a generous 35mm of additional back focus. When that snap focus is attained, a lock-down screw holds it firmly in place.

The finder is thoughtfully supplied with a pair of guidescope rings with a Vixen-style dovetail – and the finder itself is cosseted with nylon-tipped adjustment screws.

Price: £219
Supplier: Orion
For more information: www.telescope.com

There is often a precipitous moment in novice astronomy when a strengthening interest leads to consideration of that first optical acquisition. Perils lie ahead, for the unwary may either grasp an affordable but ultimately disappointing ‘toy’ from a department store catalogue, or cast caution to the wind on the great expense of an instrument whose daunting labyrinthine workings will drive the inexperienced observer to abandon the science altogether.

Which is where little (but able) scopes like this ride to the rescue. This telescope is a tube on an alt-az mount — therefore possessing an inherent simplicity that will not challenge. Yet the tube is a 4.5-inch (114-mm) f/4.4 reflector, possessing an aperture that brings a wealth of astronomy’s best to the viewer and a focal ratio providing splendidly wide-angle vistas t‘boot.

The ‘scope comes pre-assembled, so skips straight from the box ready to use. Two eyepieces yield powers of 20× and 50×, just right for those first celestial adventures. The new observer is not left to grope about in the dark either. The package also contains a Moon map, planisphere, an astronomy book and even a stellar software download. The telescope even looks the part, adorning itself with some of its potential prey.

Price: £161
Supplier: Orion
For more information: www.telescope.com