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Review of Helios ST80 Wide-Field, Short-Tube Refractor

The Helios StarTravel range of telescopes comprises instruments with apertures of 80 mm, 102 mm, 120 mm and 150 mm. The StarTravel 80 is the smallest in the range; it is a portable 80 mm, F/5 wide-field refractor. Two variants are available: one optimised for astronomical use and the other for terrestrial use. The former is the ST80; it is equatorially mounted and is supplied with a 90° star diagonal. The ST80 retails between £150-£200 and is the subject of this review. The variant optimised for terrestrial use is the ST80T; is uses the same optical tube assembly as the ST80 but comes with a 45° prism and rings/adapter to enable mounting on a standard camera tripod. (Note: a tripod is not included!)

I ordered an ST80 from Warehouse Express (http://www.warehouseexpress) in Norwich and it was delivered the following day. All components arrived in a box weighing around 5½ kg. The package included a screwdriver, spanner and simple instruction sheet to assist assembly.

The equatorial mounting has setting circles in both axes (Right Ascension or RA and Declination or Dec) with a fine adjustment screw to set the latitude to a particular location (51.5° for Ipswich). There are slow motion controls for both RA and Dec. The ST80 can be upgraded with a motorised RA drive as an accessory item. Use of tube rings rather than a fixed mounting block means the tube assembly and finder can be easily rotated to the most comfortable observing position. With slow motion control extension knobs attached, the movement in both RA and Dec axes was reasonably smooth with no serious slop or backlash at any point.

After using the ST80 on a few nights, I made two simple improvements to the equatorial mount to make the instrument easier to use when seated:

The slow motion extension cables were inconveniently placed making it sometimes difficult to achieve accurate tracking while observing. Coordination was most inconvenient when the extension cables were either fully opposite one another or together, where they tended to interfere with one another. Two replacement black plastic "electronic equipment knobs" fitted to the RA axis on both ends of the RA spindle completely cured the problem. The Dec axis retains its extension spindle.
I found when using two tube rings that the scope seemed balanced too far towards the eyepiece end. The solution was to remove the ring nearest to the eyepiece. This allowed the tube to be mounted further forward thereby curing the balance problem. I found it still possible to secure the optical tube assembly using a single ring although it needed to be more securely tightened than with two rings.

The 80 mm objective lens has an orange coating and performs very well considering the fine manufacturing tolerances required to produce such a short focal length. Defocused bright star images (e.g. Vega at 133x) either side of the point of focus displayed identical circular diffraction patterns showing that the objective is well corrected. The focussing movement is always smooth throughout the range.

The removable 6x30 finderscope provides bright clear images with a wide field of view. This makes the ST80 particularly easy to use and therefore suitable for beginners as well as more advanced observers. I found it provided a superior field of view to the 6x30 finder supplied with my vintage 60 mm refractor. A minor inconvenience occurs when locating objects at or near the zenith: a 90° eyepiece adapter for the finder would make its use on such objects much easier. An O ring supplied with the finder fits over the recessed part of the finder tube assembly which is inserted backwards (eyepiece end first) into the mounting bracket. The O ring pivots the finder at the front of the bracket allowing it to be aligned with the optical axis of the main optical tube assembly using two alignment screws located towards the rear of the bracket. A third spring-loaded point pushes the finder tube against the two alignment screws.

A universal camera mounting thread on the focuser allows virtually any 35 mm SLR camera to be attached to the scope. This is achieved through a T ring adapter (not supplied) which converts between a particular SLR camera thread and the threaded part of the focussing assembly.

Two 3.2 cm eyepieces are supplied with the ST80: a 25 mm Super Modified Achromat (SMA), an enhanced form of the standard Kellner eyepiece, and a 10 mm Kellner eyepiece. I was impressed with the optical quality of both eyepieces. The 25 mm compared very well with a 25 mm Plossl. The 10 mm eyepiece is fairly sharp but has shorter eye relief as is to be expected. The 25 mm and 10 mm eyepieces provide magnifications of 16x and 40x respectively; these double to 32x and 80x with a 2x Barlow lens. I found the ST80 performed well at all magnifications up to 133x, which I achieved with a 6 mm Plossl eyepiece and a x2 Barlow (133x was the highest magnification that I tried). Eyepieces plus Barlow lens attach to the ST80 via the 90° star diagonal which inserts into the main optical tube assembly.

The field of view using the 25 mm SMA eyepiece (without Barlow) is around 3.5° providing excellent wide-field viewing! One of the strengths of the ST80 is clearly its capability as a portable wide-field low magnification instrument. The Pleiades easily fit into the field at 16x and pretty well at 32x using the Barlow.

The 90° star diagonal provides an upright image with the left and right hand components inverted so it can also be used for daytime terrestrial observing with those constraints in mind.

Observing Report, 30 August 2000

I made observations initially at Orwell Park Observatory and later at my home in north Ipswich. I used the following telescopes for comparison purposes: at Orwell Park Observatory, the OASI 250 mm Dobsonian with 15 mm eyepiece (circa 100x) and, at home, a Prinz (Dixons 1960s vintage) 60 mm F/15 refractor with 25 mm Plossl eyepiece (40x magnification).

M57, the "Ring Nebula" in Lyra. Using the ST80 with a 25 mm SMA eyepiece and Barlow giving a power of 32x, the nebula was clearly visible, appearing as a "fuzzy star". I gradually increased magnification to 80x then 133x using a 6 mm Plossl eyepiece. Using averted vision (looking to one side of the object), I thought the image could have been marginally brighter at its edges. I found that the wider field of the ST80 finder helped locate the object much more easily than the finder supplied with the 60 mm refractor. Using the ST80, I simply pointed the finder mid-way between Gamma and Beta Lyra and found the object in the field using the 25 mm SMA with the Barlow. M57 could then be re-centred before changing to a higher magnification eyepiece. The 60 mm showed a fuzzy star with no hint of the ring when pushed to 100x magnification using the 10 mm SMA supplied with the ST80 and a 2.45 cm/3.2 cm hybrid diagonal.
M11, the "Wild Ducks" star cluster in Scutum. Using the ST80 with a 15 mm Plossl and Barlow, I could resolve stars against a hazy background. I saw a brighter star in the foreground against a background of dimmer stars and nebulosity. The 250 mm Dobsonian provided a much brighter image showing many more stars because of its increased aperture.
M13, a globular star cluster in Hercules. Again, using a 15 mm Plossl in the ST80, I could see the cluster as a fuzzy spot with granularity just starting to be visible at the edges.
Epsilon Lyrae, a quadruple star. I used the ST80 at a magnification of 133x (6 mm Plossl and Barlow) to split Epsilon Lyrae, the double-double star (components as follows: A1/A2 magnitudes 5.0, 6.1, separation 2.0"; B1/B2 magnitudes 5.2, 5.5, separation 2.3"). At around 20:00 UT I was marginally able to split Epsilon Lyrae, and at around 22:00 UT I was definitely able to do so, after seeing conditions had improved. I have never been able to split the star in my 60 mm refractor as the separation of the components is close to, if not at the limit of, its resolving power.
NGC 869 & 884, the "Double Cluster" In Perseus. The Double Cluster looked fabulous in the ST80 at 32x (25 mm SMA with x2 Barlow). Both clusters resolved into individual stars which easily fitted in the field of view. Not bad either in the 60 mm refractor at its lowest magnification of 40x using a 25 mm Plossl but the image was less bright due to the smaller aperture.

Observing Report, January 2001

I made the following observations at home.

Moon. Using the ST80 at a magnification of 133x with a 6 mm Plossl and in stable seeing conditions, features such as the "ridges" in Mare Imbrium near the crater Plato were clearly visible and the Lunar Alps looked very impressive. Very slight colouration observed at the limbs. The 60 mm refractor provided a less bright and lower contrast image due to its smaller aperture.
Jupiter. Again, a very slight amount of colour fringing visible but not obtrusive on the edges of the planet in the ST80. Both north and south equatorial belts and temperate zones seen at 32x (25 mm SMA with Barlow) and at magnifications up to 133x. At 133x, some faint detail just started to appear in the belts during moments of clear seeing.
Saturn. Very faint banding observed on the surface of the planet at 133x using the ST80. These markings were much more subtle than the belts observed on Jupiter. The Cassini division was visible during moments of clearer seeing. Observation repeated on an exceptionally clear evening (stable air) when Saturn was high in the sky: Cassini Division clearly seen plus three of Saturn's moons!

Conclusions

The Helios ST80 is an excellent value-for-money, portable telescope capable of providing good results on deep sky objects and planets if its limitations in aperture and focal length are appreciated. I feel it would suit beginners as well as more advanced observers who may want an additional portable scope. Although its short focal length means that it is not necessarily optimal for planetary observing at high magnifications, I found that it worked well at 133x when seeing conditions permitted. I'd therefore recommend an additional eyepiece (6 mm Plossl) to support lunar and planetary observing.

Readers will no doubt be interested to learn that the optical tube assembly is identical to that used in the Celestron NexStar 80 mm computerised refractor scope called the NextStar 80GT. The same optical tube manufactured by Synta has also appeared under other brand names including Orion (USA), Skywatcher and Konus (Vista).

Comparisons with other Synta ShortTube scopes are more difficult to quantify without direct experience. Reports from a variety of internet resources suggest that the 102 mm variant (in this case, Helios ST102) is excellent for low magnification wide-field observation of deep sky objects providing images noticeably brighter than the ST80. However, colour fringing on bright objects is slightly worse than the ST80 and performance degrades significantly at magnifications in excess of 150x. The conclusion on the 120 mm variant is that its performance is inferior to larger aperture Dobsonians available for around the same price (£350). I have seen no reports on the 150 mm variant. Strongly recommended are the 80 mm and 102 mm (ST80 and ST102). Of the two, the ST80 is the more popular scope.

Internet Resources

http://www.scopereviews.com/ - review of Celestron ST80 (similar specification to Helios ST80) and comparison with Televue Pronto (costs around £700 more!) Other reviews include Meade, Takahashi, Astro Physics and Celestron telescopes plus various eyepieces and accessories.

http://www.cloudynights.com/ - another site with many telescope reviews including the Celestron FS80WA - similar specification to ST80 but no longer manufactured since superseded by NexStar 80GT.

Neil Morley