Night-vision astronomy can massively improve the visual views of many deep-sky objects. No longer do you have to hunt around for ‘faint fuzzies’ – a small, military-grade night-vision eyepiece can transform your enjoyment of nebulae, globular clusters and galaxies, even from the light-polluted back-gardens of city dwellers. From a dark site the views through a night-vision eyepiece are incredible, akin to looking at photographs of deep-sky objects.
It’s not just keen amateurs whose passion for astronomy has been increased by night-vision technology. Earlier this year, the founder of TeleVue, Al Nagler, explained how night vision gives an 85mm refractor the reach of a 250mm telescope.
Now, with the release of the OVNI-M, designed specifically for astronomy by French company OVNI Night Vision, night-vision astronomy has become much more accessible. Unfortunately, though, the price remains high – up to 10,999 euros.
My existing night-vision eyepiece, a Luxembourg-made PVS-14, is extremely powerful, but it lacks a detachable front lens. This restricts observing to ‘afocal’ mode, in conjunction with a standard glass eyepiece. Afocal night vision works well, but it results in a long eyepiece stack, and can also introduce aberrations towards the edge of the field of view.
In contrast, the OVNI-M has a detachable front lens, which enables it to be used in ‘prime’ mode without the need to attach a glass eyepiece. In this arrangement stars are tight to the edge of the field of view – even with fast f/4 Dobsonians – and the stack is small, just like normal observing. The OVNI-M comes in four different grades: FOM 1800, FOM 2100, FOM 2400 and FOM 2600. FOM stands for Figure of Merit and gives a quick estimate as to the general performance level of each night-vision unit. The higher the number, the better the quality, but an FOM 1800 unit will still give great views. I would suggest the FOM 2100 is probably the best value option, given that it is only slightly more expensive than the FOM 1800. I bought a FOM 2600 version to see how the top-of-the-range model performed against my PVS-14.
The package is nicely presented in a sturdy black case. The eyepiece itself weighs 240 grams and is about 10 centimetres high; it’s far lighter than many traditional glass eyepieces, and comparable in size. It slots straight into a 1.25-inch focuser or diagonal for easy grab-and-go stargazing, and boasts all the key features that I believe are required for astronomy. These include a white phosphor tube to give natural black-and-white views of the night sky (rather than the green images produced by many older night-vision eyepieces).
It also has a manual gain to reduce or eliminate scintillation. Scintillation is a normal feature of night-vision eyepieces akin to ‘noise’ experienced by astrophotographers, but with modern phosphor tubes it can be easily controlled until it’s barely noticeable. The OVNI-M also has diopter adjustment for changing the view to suit the eyesight of the observer, and low EBI (equivalent background illumination), which results in better contrast against the night sky, thereby allowing particularly faint nebulae to be more easily seen.
It is important to note that no filters are included in the package. However, it’s necessary to use a narrowband hydrogen-alpha filter (3nm to 7nm is recommended) to observe nebulae. Also, when observing galaxies or star clusters from light-polluted skies, either a Baader 685 or an Astronomik ProPlanet 642 infrared-pass filter will significantly improve the view by reducing the impact of the light pollution and darkening the sky background.
Night-vision observing is best done at relatively low magnifications in order to ensure that the intensifier receives plenty of light. The apparent field of view of both the OVNI-M and PVS-14 might appear on paper to be quite narrow at 40 degrees, but in practice, the views are extremely immersive. I use a range of different telescopes with the OVNI-M, depending on the target objects. With my 85mm refractor I generally observe at 10× magnification, which gives a four-degree field of view and is perfect for larger nebulae such as the North America, Rosette and California nebulae. With my 400mm Dobsonian, applying magnifications between 30× and 60×, the OVNI-M provided a good image scale for galaxies, globular clusters and smaller nebulae such as the Horsehead Nebula.
The biggest advantage of the OVNI-M compared with my PVS-14 is the ability to use it in prime mode. This gives beautifully natural views with pinpoint stars, something that I have struggled to achieve in afocal mode with my PVS-14. I have included with this review some images taken on my mobile phone through the OVNI-M, which give a good indication of the actual views through the eyepiece. The night-vision tubes used within the OVNI-M are Harder Digital generation 3, which gives reassurance that you are getting a top-quality image intensifier.
The key disadvantage of using night vision in prime mode is that it requires a very fast telescope to get the best outcome, typically f/4 or lower, because the night-vision tube thrives when it receives as much light as possible. This is also why the afocal approach is so effective for night vision, since long-focal-length eyepieces act as focal reducers, increasing the effective speed of the telescope. For example, TeleVue has recently launched an adaptor that turns its 55mm Plössl into a 67mm eyepiece for night-vision users. Using the 67mm eyepiece in conjunction with a night-vision eyepiece acts as a 0.4× reducer, meaning that a slowish f/7 refractor is turned into a super-fast f/2.8 set-up, resulting in stunningly bright views of deep-sky objects.
With the OVNI-M in prime mode, I find I need to use a faster telescope such as my f/4 Dobsonian and even then I have found the views noticeable dimmer than afocal mode with a 67mm eyepiece in the same telescope. For example, in prime mode, the view through my f/5 refractor is around eight times dimmer than using it afocally with a 67mm eyepiece. That’s a big difference. Afocal mode also increases the field of view and reduces the magnification, which, depending on the target, could be seen as either a positive or a negative difference.
Despite the prime mode giving a cleaner view, my personal preference when visually observing nebulae remains the afocal mode because of its brighter view, which allows me to pick out more detail. For smaller (and often brighter) objects such as globular clusters and galaxies, the prime mode works really well with the added image scale being particularly beneficial.
Pros and cons
The OVNI-M has another advantage over the PVS-14, namely the option to remove the 1× front lens and screw in widely available C-mount lenses, such as a 75mm lens that gives 3× magnification, or with the help of suitable adaptors, add an SLR camera lens. This turns the eyepiece into an amazingly small, handheld night-vision device perfect for quick, ultra-wide-field scans of the night sky. With this type of set-up, some of the very largest nebulae, such as Barnard’s Loop or the Angelfish Nebula in Orion, or the mass of nebulae throughout Cygnus, are easily visible even in light-polluted skies, so long as you are using a suitably narrow hydrogen-alpha filter.
The OVNI-M is an impressive piece of equipment. However, there are some areas where it loses out to the PVS-14. In afocal mode, the quality of the front lens of the night-vision eyepiece is critical. The PVS-14 has an excellent front lens that works very well when paired with compatible long-focal-length eyepieces. In comparison, I have found that the front lens of the OVNI-M exhibits some vignetting and stellar aberrations near the edge of the field in afocal mode. Additionally, the OVNI-M front lens lacks the in-built thread of the PVS-14, which means that the adaptor used to attach the glass eyepiece to the OVNI-M is more cumbersome and less stable than the PVS-14 set-up.
Although the OVNI-M has a decent amount of eye relief at 18mm, I find that I have to push my eye quite close to see the whole field of view. With glasses I cannot see the whole field. In contrast, the PVS-14 has an ample 25mm of eye relief that results in very comfortable observing, even with glasses. I found that the included rubber eyecup of the OVNI-M restricted my ability to see the full field, so I replaced it with a standard rubber eyecup that works better for me.
The final slightly negative point against the OVNI-M is the manual gain control that is digital and requires holding down to operate. What’s more, it can only be adjusted one way, reducing gain to minimum and then increasing it to maximum. The PVS-14 has an analogue gain knob that can be rotated both ways and is more user friendly.
The makers of the OVNI-M are continuing to develop more accessories and night-vision products. The latest addition is the OVNI-B, which is a binoviewer night-vision eyepiece giving the benefits of using two eyes rather than one. In development are night-vision imaging solutions that will be very interesting to use. With greater availability and new options, it is an exciting time to be a night-vision astronomer. The big barrier for most people is the price. Unfortunately, because of the specialist nature of night-vision tubes, it is unlikely that the price will drop in the near future.
In summary, there are pros and cons to using both the OVNI-M and PVS-14, and the right choice will be down to personal preference. The OVNI-M’s key advantage is the additional flexibility given by the removable front lens and the guarantee of receiving a top specification night-vision tube, which are difficult to source. However, both set-ups will deliver astounding views of deep-sky objects and are wholeheartedly recommended. Night vision provides a new dimension to visual astronomy, providing exciting views for outreach events and opening up the wonder of the night sky to city dwellers, while expanding the opportunities for people in rural areas as well.
The OVNI-M night-vision eyepiece comes with a 1.25-inch barrel with thread for filters, C-mount adaptor, 26mm f/1.2 front lens, tube inspection report, and an adaptor to attach either 1.25-inch or 2-inch filters to the front lens.
The eyepiece is available from www.ovni-nightvision.com, and costs between €6,299 and €10,999, depending on FOM rating.