Omegon 2 x 54 wide-field binoculars
Galilean binoculars go all of the way back to, well, the time of the great man himself. I vaguely recall reading once that he conceived of strapping two of his telescopes together, but the source of this tale now escapes me. We do know that the first pair to be constructed were made by fellow Italian Cherubin d’Orléans in the 1670s, mounting two Galilean telescopes in parallel to achieve ‘binocular’ vision. He even incorporated individual eyepiece focusing!
In the nineteenth century, abbreviated ‘opera glass’ versions magnifying about 3× found favour in theatres – used as much to observe fellow patrons as the action on stage. A resurgence occurred in the mid-twentieth century when foldaway versions (generally 2.5 × 25mm) arrived from Japan’s developing post-war optics industry, but these were little more than toys and were never considered serious observing tools.
That has changed. Under the general description of star-field binoculars, new versions have now appeared that imbue the Galilean binocular form with the latest optics and mechanical finesse. The result is a specialised form of binocular that provides the naked eye with a significant improvement of sensitivity over a vast area of sky.
The new kid on the block is Omegon’s 2 × 54mm star-field binoculars.
What are Galilean binoculars?
Before we can commence an assessment, the nature of Galilean binoculars needs to be understood, in order to comprehend the specialised gains that they provide. In normal binocular optics we might be interested in calculating the corridor of light transmitted from the eyepiece, to see if it can be fully accommodated within the eye’s aperture, the iris. This corridor (known as the exit pupil) is calculated by dividing the front lenses of binoculars (their aperture) by their magnification. For instance, binoculars described as 7 × 50mm have an exit pupil of 50/7 which equals 7.1mm. This diameter of exit pupil can easily be encompassed by the iris of a dark-adapted young adult, whose iris can expand up to 8mm or more. It also means that for an older adult, whose iris may only creak open to 4mm diameter, much of that delivered light spills outside of the iris and is not used. This is why older astronomers should be careful to choose binoculars that provide an exit pupil more closely matching their maximum iris diameter.
In a way, it is that latter case that applies to the Galilean binocular design, since here the exit pupil is determined not by the binoculars, but by the iris of the eye itself – which in turn (working backwards down the light path) determines how much of the binoculars’ aperture is delivering light. So, reversing the above calculation, employed aperture is obtained by multiplying the user’s dark-adapted iris by magnification. A young person with an open iris of 8mm, at a magnification of 2×, effectively drinks in the light of 16mm objectives. This may not seem much of an advantage, but this still enhances the naked eye’s light-gathering power proportionate to the increased collecting area – this being four times. It is this that delivers Omegon’s advertised magnitude gain of about 1.5 stellar magnitudes. Of course, the magnitude achieved will be less for older observers, but the relative advantage provided remains about the same.
The gargantuan field of view
So, you may ask, if your eye’s 8mm iris is only garnering light from a 16mm central cut of the objectives, what is the point of supplying these binoculars with lenses 54mm in diameter? The answer lies with another peculiarity of Galilean binoculars, in that their field of view expands in proportion to the diameter of the objectives. Other things being equal, objectives of 60mm deliver twice the field of view to those having 30mm. The Omegon version having generous objectives of 54mm explains their claim of potentially delivering an impressive 36-degree field of view.
Belying the more frivolous versions in the history of Galilean binoculars, the Omegon 2 × 54mm binoculars immediately present a glossy professional appearance. They are very solidly built. Indeed, they feel rather heavy considering their relatively diminished dimensions, but in a good way, as their heft confirms their serious intent. These are made for astronomical observations and nothing like their tinny forebears.
Unlike some ultra-wide binoculars, each eyepiece has individual focus, providing a range of –5 to +3.5 (a total of 8.5) dioptres. This very generous dioptre range should enable many observers, who might otherwise have to retain their spectacles, get their eyeballs closer to the eyepieces in order to gain full advantage of the field of view available. The eye itself, of course, can also deploy its own accommodation of a few dioptres (dependant upon age). Omegon’s provision of individual eyepiece adjustment ensures that a comfortable sharp focus is always within reach by any user.
The eyepiece separation range (interpupillary distance, or IPD) is given as 60–81mm. As measured, I beg to differ by just one millimetre less. Either way, this is plenty of adjustment for human use.
So, having comprehended the technicalities and build quality, how do Omegon’s ultra-wides perform?
The usefulness of these binoculars rests on two pillars. The first is an incredible field of view, given as 36 degrees. The second is what might seem to be a marginal gain in light grasp – but more on that later.
As it happens, the gargantuan field of view is relatively easy to confirm, since Polaris and Mizar (zeta Ursae Majoris) are conveniently separated by just a shade under this (35° 36′).
It was a chilly autumn evening as I walked into the garden and looked northwards. Ursa Major was obligingly lying horizontal along the northern horizon. As the second star from the end of the Plough’s ‘tail’, Mizar (and its close companion, Alcor) were easily identified.
I carefully focused each eyepiece and adjusted their separation as precisely as I could, before going first to Polaris. I set Polaris at the very top of my field of view, then craned my vision to see if I could simultaneously include Mizar, which was hanging almost vertically beneath. I will admit that at first I could not achieve this. But these, I reminded myself, were not conventional binoculars that are able to offer generous eye relief (the distance between your eye and the eyepiece from which the whole field is visible). In a Galilean version, the field opens up the closer your eyes get to the glass of the eyepiece. Pressing my eyeballs as close to the eyepieces as possible, my brows in contact with the eyepiece focus rings, I found that with just a little bit of jiggling within my eye-socket, I could just manage to get both stars included at the very limit of the field of view.
I cannot say this achievement was comfortable but I can confirm that by backing away from the binoculars just a little, by perhaps 2–3mm, I still achieved close to the claimed maximum, perhaps 34 or 35 degrees. I can see that what can be accomplished may be down to individual physiognomies, since I would imagine that brow ridges and eye sockets will affect the attainment of varied proximities to the optics. I am happy to say that 36 degrees is achievable, but personally I would say that sacrificing one or two degrees by removing your eyeball from contact with the glass is more comfortable. I am impressed, since the optical access to such a vast area of sky is incredible and visually dramatic.
Thousands of stars more
The second advantage that these binoculars provide is a greater light grasp than the naked eye alone. As described above, the greater sensitivity is accessed not through the largesse of the binoculars’ objective lenses, but by a virtual doubling of the iris diameter.
Measuring this advantage is a little trickier than gauging their field of view, but for astronomers there is a standard candle of judgement available – this being the asterism known as the great square of Pegasus. This is an area of sky bounded by four stars, all of whom used to belong to the constellation of Pegasus, but one has since been pinched by neighbouring Andromeda. This prominent and broadly equally bright quartet of stars (Scheat, Alpheratz, Markab and Algenib) enclose an area of sky long employed for a rapid approximation of sky clarity. There are a number of stars contained within the Square, and the more that can be discerned and counted, the darker the sky must be. In this case, it serves to indicate what advantage over the naked eye alone these binoculars may provide.
On one of the darker nights that were available to me during the review, I stepped outside late into the night and (after 30 minutes of dark adaptation) strained to see how many stars I could discern by the eye alone within the approximately 200 square degree area enclosed by this celestial cage. Albeit from an area of marginal light pollution, I decided that I could confidently see three.
Again, adjusting the IPD and focus on the Omegon binoculars carefully, I cast their gaze at the same area. I now counted twelve without difficulty, perhaps thirteen. Admittedly, most were faint, but there were stars now visible where before there were none. This simply confirmed my previous experience of looking at other areas, particularly into the band of the Milky Way, where regions of sky visually devoid of stars simply burgeoned with them when these binoculars were deployed.
While the constellation of Pegasus was conveniently placed above me, it meant that neighbouring Andromeda had a prize of its own to offer, being the Andromeda Galaxy (M31). From my site, I can catch sight of it on good nights. Through the Omegons it was an easy object.
The advantage proffered by Omegon is that there is a relative gain of about 1.5 magnitudes over the naked eye alone. This may not seem much, but be mindful that magnitude is a logarithmic scale, and that the gain in sensitivity is about four times. As example, the naked eye at its best might be able to see 2,800 stars in the celestial sphere down to magnitude +5.5. If you can include stars just a magnitude fainter, then that cache balloons to 9,000. Considering these figures, it soon becomes obvious how differently the sky can look with a gain of just one-and-a-half magnitudes. Getting access to a profoundly dark sky where the naked eye might peer down to sixth magnitude, the advantage gained by these binoculars can garner a total of about 26,000 stars.
While it is true that a conventional pair of binoculars, such as 7 × 50mm, can go fainter, their blinkered gaze is generally limited to a field just seven degrees across. As an indication of the Omegon’s superiority, field-wise, in mid-November I was able to capture the Moon, Jupiter and the Hyades in one breathtaking gaze.
Naked-eye vision on steroids
Although pitched for enhancing views of the night sky, the Omegon 2 × 54mm wide-field binoculars do serve well in daytime too, despite the low magnification, simply by channelling additional light into the eye. (En passant, older astronomers can regain their youthful view of the bright daytime world again with the benefit of these artificially enhanced pupils.) One afternoon I spent an enjoyable few minutes observing a duo of buzzards circling high above me. Not only was I afforded a cleaner, brighter view of their lazy aerial motion, but the binoculars’ wide field meant that I had to move my gaze very little to encompass their circular flight.
As my autumn review fell within November, I discovered an unforeseen use for these binoculars. A gain of 1.5 magnitudes may be useful for observing the sky, but it comes in handy for watching fireworks too – especially other people’s! Airborne sparks remain pleasurably visible long after fading from naked-eye visibility. The extremely wide field suits this pyrotechnic purpose like a glove.
These Galilean binoculars should be considered, not as binoculars in the usual sense, but as naked-eye vision on steroids. They have applications in getting accustomed to constellations (for even the fainter ones become punchy), for simply enjoying vast swathes of star fields, comets, catching fainter meteors that might otherwise be lost and hunting for the new vermin of the sky, satellites. I can also see a use in the observation of aurora, although the Sun did not oblige in supplying one during my review.
These glasses are a portal into an entirely different way of observing the sky. Galileo went on to improve his initial optics, but if he had known his first configurations would find their way into use as a serious low-power astronomical instrument, he would be so pleased. Enjoy.
Steve Ringwood is a regular contributor to Astronomy Now.
