A Work Commenced July 28 2022
Product: Helios Star Field 2 x 40WA
Country of Manufacture: China
Coatings: Fully Broadband Multi-Coated
Eye Relief: 10mm
Close Focus: 2m advertised
Field of View: 445m@1000m(24 Angular Degrees)
Weight: 189g advertised and measured
Size: 12.2 x 4.9 x 3.8cm
Accessories: Neck strap, semi-hard zipped case, microfibre cloth, instruction sheet
UK Price: £99.00
There’s nothing new under the Sun, and then some. Opera glasses have enjoyed a long history owing to their ability to generate low power, wide-angle views, enabling the theatre goer to get an ultra-stable view of the stage. In the past few years though, the opera glass has been modified to create a new type of observing experience under the starry heaven – enter the super-wide angle constellation binocular, employing powers not much more than 2x and offering up exceptionally large fields of view up to 36 degrees or so. Several models offering this kind of experience have been launched by companies such as Vixen, Orion USA and Svbony. But recently the well-known company Helios, now owned by Optical Vision Limited, has also produced their own rendition of this binocular to sate the demand of this niche observing experience; enter the Star Field 2 x 40 WA Galilean binocular. Having owned and tested out the Svbony SV 407 2.1 x 42, I was curious to learn about the Helios model, owing to its significantly smaller size and lighter weight, which would naturally lend itself to longer hand-held views.
Before getting into the details of this model, let’s look at the optical concept behind all these devices. First off, these are not true opera glasses – the eyepieces have additional lens elements to reduce aberrations inherent to the Galilean telescope design and greatly widen their field of view. This means that there will exist models that boast the same fields of view but at higher power, mostly attributed to the design of the eyepiece. The next thing to remember is that the human eye cannot harness the full light gathering power of these binoculars. On paper the exit pupil of the Helios Star Field 2 x 40 is 20mm. The human eye pupil however has a maximum aperture of 7mm, and as we age the aperture of the exit pupil decreases somewhat. So, let’s just say we have a 6mm exit pupil(which is probably realistic for a middle-aged individual like me). Thus, the effective aperture will be 2 x 6 = 12 mm. So, effectively we’re dealing with a 12mm binocular offering a 2x magnification. So what’s the deal with the 40mm aperture of the objectives? Well, it turns out that in the Galilean optical design, the field of view it delivers is dictated by the size of the objectives – the larger their size, the greater the effective field of view. The reader will note that this principal does not apply to conventional binoculars.
The 2x magnification will darken the sky by a factor of 2^2 or 4 times, and it’s the combination of the effective 12mm aperture and the 4-fold darkening of the sky that limits the faintness of stars visible through the instrument. In practice, this results in a boost of about 1.5 magnitudes – a useful gain in sensitivity over the naked eye view.
Owing to the nature of the design of these super-low power modified Galilean binoculars, there is no well-defined field stop and since the exit pupil of these designs is virtual, that is, it’s positioned inside the optical train, there is no fixed locus to image the field of view. What this means in practice is that the closer one can get to the ocular field lenses the wider the field of view experienced. Unfortunately, eye glass wearers will not, in general, be able access the same size fields as non-eye glass wearers, so these are ideally suited to the latter group of individuals. Finally, despite their advertised field sizes, off-axis aberrations significantly curtail the size of the field that offers up well corrected stellar images. And this is where the quality of the optics gets factored in. Poorer quality instruments will manifest off-axis aberrations closer to the centre than better made brands.
Now let’s take a closer look at the Helios Star Field WA 2 x 40
The first thing I noted about the Helios Star Field is its light weight. At only 189g, it’s nearly half the weight of the Svbony SV 407 2.1 x 42. And its considerably smaller too. Take a look at the size comparison below:
The optics are fully multicoated on all lens surfaces. I was unable to detect any internal reflections when pointing the instrument at a bright artificial light source.
The eyepieces must be adjusted individually by turning them clockwise or anti-clockwise. The dioptre compensation range is from -5 to +3. Turning the oculars is slow but all the while smooth.
The chassis is made from high-quality machined aluminium. And while lightweight, it has the feeling of quality when you hold it in your hands. Indeed, the Svbony model, in comparison, is just plain over-built. There’s absolutely no need for a device like this to weigh so much!
The eyepieces have 10mm of eye relief; that’s not bad considering other models only have 8.5mm or so. That said, one of the things that niggles me about all these devices is that the lenses can get smudged from eyelashes rubbing against the surface, necessitating more frequent cleaning. This is not directed at the Helios Star Field 2 x 40 per se. All the other models have the same issue.
There’s no provision to mate the Star Field to a tripod, but such a lightweight device doesn’t need one. Indeed, I think it even defeats the purpose of these devices which were surely created to enjoy hand-held.
The instrument comes complete with a quality neck strap but I elected not to use it as it is so lightweight and small enough to put in a medium sized pocket.
I love the carry case that accompanies the instrument; its sturdy hard shell will protect your investment from knocks and bumps while not in use. It zips closed to keep out dust and moisture and has a neat little carry strap attached for transport.
All in all, the Helios Star Field WA 2 x 40 is a very nicely engineered product that feels good in the hand; top marks for ergonomics!
Daylight Optical Testing
If I’m being honest, I was quite underwhelmed by the performance of the Svbony SV 407 2.1 x 42. It had too much off axis aberrations in both daylight and night-time tests. These observations coloured my opinion of these devices so much that I was under the impression that they were all pretty much the same. Thankfully, nothing could’ve been further from the truth! Comparing the Helios Star Field 2 x 40 and Svbony 2.1 x 42 in A/B tests confirmed that the Helios was in a completely different league to the Svbony. The Helios was slightly sharper on axis, with better contrast, and had a much larger sweet spot than the Svbony. I would estimate that the effects of field curvature were not at all intrusive in the central 50 per cent of the field of the Helios Star Field but was more like ~ 30 per cent in the case of the Svbony. These differences were striking and completely unexpected!
After adjusting the eyepieces to accommodate my eyes and setting them at infinity focus, I was immediately taken by the huge contrast boost, as well as the resolution gain over the naked eye. The image showed colours far more vividly and I was able to see much finer details on high-contrast objects like the grain of wooden fences in the middle distance. Field depth is extraordinary in the Helios Star Field 2 x 40. I estimated close focus at infinity to be about 4.5-5m! After a few minutes glassing with this instrument, the view becomes so immersive and thought-provoking you can easily forget that the view is magnified. I was especially thrilled when I brought the instrument for a stroll through my local woods, where I could view vast swathes of forest with excellent clarity and depth perception. It was like having bionic eyes! Adjusting the eyepieces, I was able to obtain tack-sharp images of Red Campion beds as close as 1.9m away, so a little better than advertised. Indeed, when they come within about 10-15 metres from you, the Helios Star Field 2 x 40 served up excellent details of Blackbirds, Chaffinches and Song Thrushes foraging in the leaflitter on the forest floor. I was even lucky enough to watch the climbing antics of a little Tree Creeper inching its way up the trunk of a majestic Scots Pine some 12 metres in the distance.
One of the most unexpected dividends this neat little instrument provided was its ability to be used profitably in a moving vehicle. I brought the Helios Star Field along with me in the car. My wife was driving, and I was sat in the front passenger seat. We arrived at a stretch of road a few miles long between Strathblane and Milngavie, where I was able to enjoy stunning views of the Campsie Hills drenched in gorgeous evening sunshine. The enhanced resolution and contrast over the naked eye view turned already stunning views into sublime vistas! The magnificent escarpment came alive with intimate details of the exposed igneous rocks near their summits, with wonderful views of careening waterfalls and the ravines they had carved out over the millennia. Stunning too were the vast swathes of bracken and heather traversing the lower slopes of these ancient hills. I was amazed just how relaxing the views were. These kinds of mobile observations are quite beyond the powers of regular binoculars. If you’re ever travelling through great mountain ranges, these super-low power, wide-angle glasses are sure to enthral you with the details you can make out – and you won’t feel in the slightest way discombobulated for doing so!
Night Sky Testing
To be continued……………………