I still remember with satisfaction the moment I bought my first 100mm binoculars. While researching the observational capabilities of an instrument with such a large diameter, I came across some articles that talked about the incredible observing experiences that could be had with an instrument of that diameter. After gaining some experience with my first 22x100 and a subsequent 25x100, I wrote an article on the topic: “100mm binoculars, what can you see?”
With great pleasure, therefore, appreciating this format very much, I present to you my impressions regarding the bOberwerk 25×100 ED ULTRA Porro prism inoculation, which is available at a price of 949 euros and is equipped with FK61 ED low dispersion glass objectives.
It was sent to me, as always, by the European distributor of Oberwerk, that is to say Oberwerk.eu. In this article and the accompanying video review, we'll explore the technical features, strengths, and weaknesses of this instrument, as well as my practical impressions. Happy reading and enjoying!
The binoculars come with a sturdy metal case, containing a few essential accessories to get the most out of them. You'll find caps for the large 100mm objectives, an eyepiece cap, and a shoulder strap. However, given the impressive size of these binoculars, this last accessory may be superfluous for enthusiasts. A small instruction manual and an optics cleaning cloth are also included.
I also highly recommend purchasing the Riser, available on the official American website (ask the European distributor if they can supply it) because depending on your interpupillary distance the binoculars may touch the video head you are using.
As you can see in the video and in the images included in the article, The binoculars are equipped with Porro prisms. My electronic scale estimated a weight of 4043 grams without caps and without the plate for connecting to a photographic tripod. As is standard practice, a large central bar provides greater stability and prevents misalignment of the two optical tubes, as well as allowing for excellent balance of the instrument when mounted on photographic tripods.
The design is very nice, with a partial protection of the binoculars by a dark green armor with an orange peel-like finish, which offers an excellent grip and is relatively easy to clean. Some parts are exposed to knocks and scratches, such as the area of the cell that contains the objectives and the section where the optical tubes meet the prism area, but these are not binoculars that you can carry over your shoulder through woods and brambles. In the eyepiece area, the main technical data of the binoculars are present, such as the format, water resistance and the linear field, which is equal to 46 meters by 1000 meters. Furthermore, the multilayer anti-reflection coating and the BAK-4 glass prisms are mentioned.
FIG.1 – The Oberwerk 25×100 ED ULTRA binoculars in all their majesty
As for the assembly, I tested different solutions, from TR3 Oberwerk tripod with patented system slip-stop on which I mounted the fork built by Elio Biffi up to the tripod Stabilo 100 Cartons with Fluid Head Focus 10 Cartons, which have demonstrated excellent holding power and have proven to be a perfect solution for supporting this instrument.The central bar allows you to easily balance the instrument for both landscape and astronomical use, thanks to the large knob that is easy to operate even with winter gloves.
Built with metallic materials, theThe structure is completely waterproof and filled with nitrogen. One point in its favor compared to similar products is the presence of Porro prism supports with precision floating plate, while the optical tubes are reinforced and hinged to ensure excellent shock resistance. It is certainly a well-designed product, whose price reflects this quality, despite being significantly lower than angled binoculars with low dispersion optics.
FIG.2- A close-up of the initials printed on the lid in the prism area
Model
Weight
Dimensions
Oberwerk 25×100 ED ULTRA
40430g
L=45.72 cm, W=25.4 cm, H=10.16 cm.
As for the focusing system, the Oberwerk 25×100 ED ULTRA It features a single focus on each eyepiece, with +-5 reference marks showing the total travel to focus the images. Focusing proved to be extremely precise, allowing for perfectly sharp images. Using a single focus not only offers greater precision, but also the ability to use at least one eyepiece in case the other is damaged, as well as ensuring better waterproofing. The declared minimum focusing distance is 20 meters, but the model I tested reached over 35 meters. From there to infinity, you need to rotate the eyepiece rings counterclockwise by just under a quarter turn.
FIG.3 – Focusing is individual for each eyepiece
Model
Minimum focusing distance of the tested specimen
Direction of rotation
Reaching infinity from the minimum distance
Oberwerk 25×100 ED ULTRA
38 meters
counterclockwise
Just under 1/4 turn
OPTICS
Goals
FIG.4 – A close-up of the low dispersion ED lenses of the Oberwerk 25×100
In the video you can see some shots taken by placing the mirrorless camera close to the binoculars' eyepiece and you will also see that Images in the center of the field of view are always very sharp and contrasty. White tones are slightly warm., but personally it doesn't bother me at all; in fact, I prefer it in foggy situations, where it offers better control than products with more neutral optics.
It is important to point out that when I speak of a slight warm tone, I do not mean that the lens makes whites yellow, but rather that, compared to very neutral instruments, even for photographic use, this slight shift towards a slightly warmer tone is noticeable.
Eyepieces
The eyepieces offer a claimed wide-angle field of 46 meters at 1000 meters, corresponding to a true field of 2.63 degrees, generating a remarkable apparent field of nearly 66 degrees. The rubber lens hoods are soft and can be lowered completely to allow use by eyeglass wearers. I really appreciate Oberwerk's transparency regarding the actual eye relief, declared at 14 mm. Some manufacturers tend to be more generous in their performance claims, so it is advisable, as already pointed out on the official website by Kevin Busarow who Eyeglass wearers should try the instrument before purchasing.
FIG.5 – Eyepieces provide a wide-angle field of view
I personally measured the distance from the center of the field lens to the edge of the unretracted lens hood and got a measurement of 14.1mm, in perfect agreement with what Oberwerk declared. With my 66mm interpupillary distance, the eyepiece distance is approximately 17.20mm. However, thanks to the softness of the eyecups, you can enjoy optimal comfort as they gently adapt to my brow bone and nose. I think these binoculars are also suitable for people with a slightly shorter interpupillary distance than mine.
I have estimated the interpupillary distance of this instrument to be between 62 and 77 mm, While Oberwerk clearly states 57.75 mm. However, it is important to note that this measurement can vary from specimen to specimen, and I agree that it would be quite difficult to observe with an interpupillary distance of only 57 mm, as the distance between the eyepieces would be very small.
Model
Field lens diameter
Barrel diameter
Distance between eyepieces with a distance of 66 mm
Oberwerk 25×100 ED ULTRA
25 mm
50 mm
17.20 mm
Prisms
The prisms are made of BAK-4 glass. There's very little light scattering outside the exit pupil, which indicates excellent workmanship. The fit stop is clean, and there's no vignetting at the edges of the field of view. These binoculars are definitely superior to my 25×100 achromatic binoculars, which cost half as much and which I often use as a reference.
FIG.6 – The exit pupil showed the presence of little diffuse light at the edge
Anti-reflective treatment
I assume the anti-reflective treatment is identical to the BT XL angled series .I tried comparing it with the equipment I own, and I have to say that this multi-layer anti-reflection coating on every surface does its job very well. Compared to my inexpensive 25x100, in the reflection test of my image, I can see very little detail, which demonstrates the anti-reflection coating's excellent ability to prevent unwanted reflections and guide light to the prisms. Great job, Oberwerk!
CHROMATIC AND GEOMETRIC ABERRATIONS TO BE MADE
Chromatic aberration at the center of the field
I think that in this case too an excellent job has been done. FK61 ED low dispersion glasses in the 25×100 binoculars allow for excellent correction of residual chromatism. While observing spacer spheres and power line cables, such as the classic red and white sphere visible in this photo, looking with one eye in the center of the field of view, I could only notice a faint, minimally invasive blue-green halo that almost completely disappears when looking with both eyes. In very bad observation conditions, such as a snowy landscape in strong backlight, I perceived a slight residual chromaticism, obviously the FK61 ED similar to the FPL51 does not reach the performance (and the production cost) of the FPL53 but compared to achromatic binoculars, an excellent result has been achieved.
FIG.7 – Difficult situation highlighted by extrapolating a frame from the video obtained by placing the mirrorless camera close to the eyepiece.
It's important to remind readers that the perception of chromatic aberration is highly subjective and that I'm personally particularly sensitive to it. Even on bright days and observing natural details like houses, trees, and mountains, I must admit that I greatly appreciated the reduction in residual coloration in these binoculars, which is practically unmatched by typical entry-level 25x100 binoculars.
Lateral chromatism
Lateral coloration is noticeable when moving away from the center of the field of view, but it is not as invasive as in cheaper 25×100 binoculars.
Field curvature
When analyzing field curvature, I always consider the needs of the optical instrument's user, which can vary from stargazers to landscape enthusiasts. During daytime use, I checked the sharpness of a bolt on a crane at a construction site about 250 meters from my house. I noticed that the sharpness begins to diminish towards the center of the field with the 90%. I think this is excellent performance for a fixed magnification binocular where you're looking for a balance between performance, weight, and quality.
It is important to remember that our subjective perception of the image can vary with age and when using both eyes. In daytime use, I can confirm that these binoculars offer an almost completely flat field of view, still allowing me to perceive details even at the edges of the field of view. However, during astronomical observation, field curvature-related defects, such as coma and astigmatism, become more evident at the edges of the field of view. I'll discuss this further in my impressions in the next section.
Angular distortion
Regarding angular distortion, I tried observing lampposts at long distances, since these binoculars do not have a very high minimum focus. I can confirm that I did notice some pincushion distortion.As for the distortion in the magnification that could deform circular subjects, such as the spheres or electrical pylons just mentioned, I have not noticed a percentage so high as to compromise the observations. Placing a sphere in the center of the field and moving toward the edge, I noticed a slight ovalization, but it was subtle. Again, I really appreciated the effort to contain the geometric distortions.
I cannot be an optimal yardstick for the “rolling ball” effect; I invite young readers to consult the glossary to understand what I'm talking about. However, I must say that although I didn't use these binoculars much in the way of fast panning, I found it relaxing when observing the landscape. I remind readers that designers have to make compromises when building an optical design, and I think these binoculars are definitely suitable for observing star fields.
Other aberrations
To assess the presence of coma and astigmatism, I conducted two separate tests. First, I used the classic variable star test, , using the one sold by Geoptik with 50 micron optical fiber.. Next, I analyzed some stars in the sky, focusing in particular on Capella, one of my favorites during the month of February. Generally speaking, I must confirm that the star images are satisfactory up to the 80-85% from the center of the field of view, after which the presence of a little coma and astigmatism becomes evident.
Star Test
CM (maximum sharpness field)
CU (usable field)
CI (Unusable field with very degraded stars
Oberwerk 25×100 ED ULTRA
75
15
10
USAF CHART TEST AT 35 METERS
Since I couldn't focus at that distance, I avoided presenting a test at greater distances because I wouldn't have had a yardstick to compare it with other instruments.
FIELD TEST
Birdwatching
For nature observation, it certainly doesn't look like a classic birdwatching binocular, as it is equipped with individually focusing eyepieces and has a minimum focus that is more suitable for long distances. However, if you are a bird of prey enthusiast and enjoy recognizing them even from long distances, these binoculars are very useful for several reasons. First of all, it costs less on average than a decent quality spotting scope. Although it doesn't have a zoom eyepiece, The 25x used with both eyes provides a discernment ability that I consider similar to that obtainable with a 35x spotting scope.
Also, if you can use a stable support, like the one I used for my observations, Straight binoculars make it easier to target even elusive birds of prey such as peregrine falcons. I have taken these binoculars several times to the rocky face of Monte Poncione in the province of Varese to admire the flight of these fantastic birds of prey. Even if a minimum of chromatic aberration is sometimes noticeable, the images are always very satisfying and decidedly bright.
FIG.8 – My wife observes a buzzard above the Valcuvia thanks to the high magnification of these binoculars
Used on a bird perch, it shows an incredible array of details, from raptor nests located up to 800-1000 meters away to buzzard perches, marsh harriers and more. It is a completely different instrument from a spotting scope, but for certain types of observations, such as long-term censuses, it is undoubtedly more effective.
Landscape observation
Considering its wide apparent field, the edge rendering which I consider excellent, its magnification and brightness, it is certainly a pair of binoculars that I highly recommend for terrestrial observation enthusiasts who can invest less than 1000 euros and already own an excellent tripod. With its 25x magnification and the use of both eyes, it is possible to observe details that would be impossible to see with a classic 10-15x magnification binocular, even when placed on a tripod. HI have seen several times on Mount Piancavallo, 32 km away from my observation point, herds of deer, groups of snowshoers and people trying to reach the summit, all with extreme ease and comfort, with excellent detail, medium-high contrast and good containment of chromatic violation, which becomes excellent when compared to the classic 25x binoculars that cost 300-400 euros.
FIG.9 – With these binoculars and a panorama like this you will hardly want to go back home
I think it's a great tool for those who own, for example, a house or a cabin from which to admire the view. It definitely needs a stable stand, and in that case I would advise you not to skimp too much on the purchase. It could also be considered a definitive tool, moreover, if I were to analyze its classic design it is also a beautiful piece of furniture.
Astronomical observation
For astronomical observation, I greatly appreciated the brightness of these binoculars, which, at the same magnification, I consider similar to that of classic angled binoculars of the same diameter but significantly more expensive. I was particularly impressed by the star pinpointing at the center of the field, which in this example was very similar to that of a high-quality refractor. The perception of detail on faint objects was comparable to that of a telescope of about 130 mm in diameter, with the obvious benefit of a wide field of view at low magnifications, allowing for rapid navigation of the sky with a speed and ease of use that only binoculars can achieve. The nebula M42 appears with a clear, mottled grey shape, decidedly large, even M78 is easily visible under medium polluted skies and under a fair sky at 1000 meters altitude it is already possible to perceive differences between M81 and M82 which easily show their dissimilar shape. The Pleiades and Hyades are wonderful objects to observe with 25x100 binoculars and it is an experience I invite you to have in the course of your life.. The moon exhibits only a very slight spurious halo if brought to the edges of the field, in the centre the images are very sharp and contrasted and at 25X it is already possible to perceive dozens of lunar craters, the Alps, the Apennines, all the lunar maria and the different differences in albedo of the surface. In this case, the performance is comparable to that of a 115-128 mm refractor equipped with at least 30-35x magnification. Jupiter displays a rim edged with a slight chromatic residue and clearly displays the NEB and SEB.
In short, under a decent sky, I am firmly convinced that these binoculars could become a definitive tool for many enthusiasts.
FIG.10 – Even under moderately polluted skies, the 25×100 “OBI” will make many amateur astronomers fall in love
PROS AND CONS
Pros:
FK61 glass lenses
Robust and waterproof
Wide-angle field of view
Good containment of chromatic and geometric aberrations
Greater sharpness and contrast than lower-cost 25x100 binoculars
Competitive with classic angled binoculars for deep sky and terrestrial observations
More suitable for outdoor use than an angled one for better waterproofing
Defects:
Field not completely flat
Presence of chromatic aberration in some circumstances, when compared to much more expensive angled binoculars with SD glass
Need for a sturdy tripod or parallelogram mount for optimal astronomical observation
Pupillary extraction to be checked for spectacle wearers
FIG.11 – ED lenses in this format are a clear improvement, especially for terrestrial observation enthusiasts
IN SUMMARY
In summary, I find the Oberwerk 25x100 ED ULTRA to be an excellent all-rounder suitable for both landscape observation and astronomy, especially deep-sky objects like nebulae and star clusters. Thanks to the FK61 glass, it significantly reduces chromatic aberration compared to lower-end 25x100 binoculars, offering a nearly fully usable field of view and excellent star pinpointing in the center of the field for astronomy enthusiasts. For those who can't afford to spend significantly more on a pair of 100mm angled binoculars with interchangeable eyepieces, these binoculars are an excellent choice and a clear improvement over the lower-end instruments that dominated the market until a few years ago. I prefer them for purely terrestrial use to classic angled binoculars because of their greater robustness and waterproofing and because they are "classic" binoculars, without frills and with fixed eyepieces. Once again, Oberwerk proves that it can satisfy demanding enthusiasts who want to observe the sky and nature at high magnifications without having to invest a fortune.
Thanks to Kevin Busarow of Oberwerk.com for the valuable information provided and Pietro Romagnoni of Oberwerk.eu,.
DISCLAIMER
Binomania is not a store. On my website, you will only find reviews of sports, photographic, and astronomical optical products. My opinions are impartial, as is the duty of any journalist, and I do not take any percentage of any sales from any product purchases. For this reason, if you would like to purchase or have information on any price changes or new products, I recommend visiting the official website. Oberwerk.com By clicking on the banner, which is the only form of advertising in this article. Thank you.!
Piergiovanni Salimbeni - Journalist and independent tester, founder of Binomania.co.uk, with over 25 years of experience in evaluating optical and digital instruments. It offers practical reviews and personalised advice for informed purchasing choices.
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