Binoculars review

Kowa BD 10x42 XD Prominar

Kowa BD 10x42 XD Prominar
20 January 2016
Kowa is a Japanese producer with a limited line-up which, nevertheless, is quite well-known on the market. Most of it consists of ornithology instruments which not so long ago were entirely produced in Japan.

Lately, though, Kowa have show several series of binoculars produced in China and the BD XD Prominar is the best of them. It features models with following parameters: 8x32, 10x32, 8x42, 10x42, 8x56, 10x56 and 12x56.

Kowa BD Prominar XD 8x32, 10x42 and 8x56.

All of these pairs of binoculars are rather small when compared to other devices in their respective class. They are equipped with Schmidt-Pechan roof prisms made of BaK-4 glass and are phase-correction coated. They also feature a highly reflective dielectric C3 coating. The producer mentions two XD elements most likely made of low dispersion glass. All air-to-glass surfaces in optical paths are supposed to be multicoated as well.

The casings of the binoculars are made of magnesium composites; they are waterproof (but not submersible) and nitrogen-filled.

Buyers get objective cups, a joined eyepiece cup (rainguard), a strap and a hard case in the box. All products come with a 10-year guarantee of the producer.

  • Lornetka Kowa BD 10x42 XD Prominar
  • Lornetka Kowa BD 10x42 XD Prominar
  • Lornetka Kowa BD 10x42 XD Prominar
  • Lornetka Kowa BD 10x42 XD Prominar
Manufacturer data


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Magnification Lens diameter Angular field of view Prisms Eye relief Weight Price
10 42 108/1000(6.2o) BaK-4/roof 18 mm 655 g 1645 PLN
Results of the review
Real front lens diameter Left:   41.97+/- 0.05 mm
Right:  41.93+/- 0.05 mm
8 / 8.0 pkt
Real magnification 10.05+/- 0.1x 3/3.0
Transmission 83.9+/- 1% 11/25.0
Chromatic aberration Noticeable in the centre but still acceptable. On the edge a bit lower than medium. 5.4/10.0
Astigmatism Moderate. 6.5/10.0
Distortion The distance between the first curved line and the field centre compared to the field of view radius:76% ± 3% 9/10.0
Coma Starts already in the middle of the field of view and on the edge is between medum and high. 3/10.0
Blurring at the edge of the FOV The blur occurs in a distance of 83% ± 3% from the field of vision centre. 6/10.0
Darkening at the edge the FOV Visible. 3/5.0
Whiteness of the image In the red part of visible spectrum the transmission level is by 6% higher than in the middle of the range. A bit yellowish hue. 4.2/5.0
Collimation Perfect. 5/5.0
Internal reflections
Left: Right:
Kowa BD 10x42 XD Prominar - Internal reflections - Left Kowa BD 10x42 XD Prominar - Internal reflections - Right
Very sensible appearance of the area near exit pupils.
Housing Small for the 10x42 class. Comfortable to hold. Green rubber armour, a bit rough which sticks out a bit near the objectives. Rubberized eyecups with 4 positions. Produced in China. 7.5/8.0
Focusing Huge, silver and ribbed central wheel with a working range of 550 degrees. It moves smoothly and is well-damped. Individual focusing through a ribbed ring on the right eyepiece. It moves the outer element. It’s a pity the producer didn’t copy the solution you see in the 56 mm class where you have a joystick and completely inner focusing. 4.5/5.0
Tripod There is a comfortable exit. 3/3.0
Interpupilary distance from 57.5 to 76.6mm 5/6.0
Closest focusing distance 1.40 m 2/2.0
Eyepieces FOV Apparent field of view of 61.4 deg (according to simple formula) and 56.4 deg (according to tangent formula). 11.5/20.0
Field of view Measured by us amounted to 6.11 +\- 0.03 degrees and it was slightly narrower than stated by the producer. Sensible size of the field for this class of equipment. 5.5/8.0
Quality of the interior of the barrels Properly darkened and matted tubes with a lot of apertures and ribs. The bottom is too light. On the prisms you can notice some tiny dots. Some specks of dust. 3/5.0
Left: Right:
Kowa BD 10x42 XD Prominar - Vignetting - Left Kowa BD 10x42 XD Prominar - Vignetting - Right
OL: 0.66%, OR: 2.24%
Prisms quality Good quality BaK-4. 8/8.0
Antireflection coatings Green- yellow on the objectives, green-yellow-purple on the eyepieces, greenish on the prisms. Strong reflections from the prisms, medium intensity of coatings. 4/5.0
Warranty [years] 10 4.5/6.0
Final result
132.4 / 190 pkt
Econo result 0pkt.


  • handy but solid casing,
  • moderate astigmatism,
  • negligible distortion,
  • good colour rendering,
  • nice areas near exit pupils,
  • image sharp already from1.4 metres,
  • good quality BaK-4 glass.

  • too high coma.

The Kowa BD 10X42 XD Prominar is undoubtedly a great pair of binoculars – small, relatively lightweight, stylish, with good parameters, good and momentarily even very good optics. What’s important in our test it had just one slip-up connected to the coma correction. If you wanted to nit-pick you could also mention its slightly too low transmission level.

Unfortunately it is not as good as, say, the Olympus 10x42 EXWP I, the Vanguard Endeavor ED II 10X42 or the Vortex Viper HD 10X42, instruments which were real hits of our 10x42 class ranking but still it remains cheaper than them. Because of that lower price its direct rivals are rather the Nikon Monarch 7 10x42 and the Alpen Wings ED 10x42 and both these models are able to take away a big market share from the Kowa. The Alpen is even a bit cheaper, its result in our test was a tad higher, its field of view is wider and it is physically lighter. The Nikon for a change is a bit more expensive but its field of view is noticeably wider and, overall, that brand name is far more recognizable than Kowa.

Still if the design of the Kowa suits you and the coma correction is not an important requirement, the purchase of this instrument is highly recommendable. It would be difficult to find an instrument which, for that price, would be noticeably more enjoyable.