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Binoculars review

Kowa BD 8x56 XD Prominar

Kowa BD 8x56 XD Prominar
11 November 2015
Optyczne.pl 
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.

Pictures
  • Lornetka Kowa BD 8x56 XD Prominar
  • Lornetka Kowa BD 8x56 XD Prominar
  • Lornetka Kowa BD 8x56 XD Prominar
  • Lornetka Kowa BD 8x56 XD Prominar
Manufacturer data

Manufacturer:

Kowa
web site

Distribution / Sales:

Ecotone
web site

Magnification Lens diameter Angular field of view Prisms Eye relief Weight Price
8 56 105/1000(6o) BaK-4/roof 23 mm 1150 g 1849 PLN
Results of the review
Real front lens diameter Left:   55.15+/- 0.05 mm
Right:  55.21+/- 0.05 mm
4 / 8.0 pkt
Real magnification 8.02+/- 0.1x 3/3.0
Transmission 84.2+/- 1% 11/15.0
Chromatic aberration Low in the centre, on the edge noticeably lower than medium. 7.8/10.0
Astigmatism Very nicely corrected. 8.3/10.0
Distortion The distance of the first curved line from the field of view centre compared to the field of view radius: 41% ± 4% 4/10.0
Coma Appears in a distance of about 75% of the field of view radius and on the very edge is between medium and high level. 6.5/10.0
Blurring at the edge of the FOV Blur occurs in a distance of 83% ± 3% from the field of view centre. 6/10.0
Darkening at the edge the FOV Negligible. 4.5/5.0
Whiteness of the image 89% of transmission in red. The hue of images a bit yellow-green. 3.8/5.0
Collimation Perfect. 5/5.0
Internal reflections
Left: Right:
Kowa BD 8x56 XD Prominar - Internal reflections - Left Kowa BD 8x56 XD Prominar - Internal reflections - Right
Some light areas away from the pupil.
3/5.0
Housing Quite slight for the 8x56 class. Comfortable to hold. Green rubber armour which clings to hands quite well. The rubber sticks out near objectives a bit. Rubberized eyecups with three possible positions. Produced in China. 7.3/8.0
Focusing Huge, silver and ribbed central wheel with a working range of as much as 760 degrees! There is a lot of turning but it moves smoothly and is well-damped. Individual focusing through a joystick positioned next to the central wheel. Nothing moves outside. 5/5.0
Tripod An exit with a moderately comfortable access. 2.5/3.0
Interpupilary distance from 58.3 to 73.8mm 4/6.0
Closest focusing distance 3.0 m 2/2.0
Eyepieces FOV Apparent field of view of 46.4 degrees. 4/10.0
Field of view Measured by us amounted to 5.78 +\- 0.04 degrees and was by 0.22 of a degree narrower than stated by the producer. A quite weak field for this class of equipment. 4/8.0
Quality of the interior of the barrels Dark, decently matted tubes. A lot of apertures and ribs. Grey bottom. The left tube is flawless, in the right one we found some specks of dust and small damp patches (?). 2.6/5.0
Vignetting
Left: Right:
Kowa BD 8x56 XD Prominar - Vignetting - Left Kowa BD 8x56 XD Prominar - Vignetting - Right
OL: 0.80%, OR: 3.77%
4.5/8.0
Prisms quality Good quality BaK-4. 8/8.0
Antireflection coatings Green on objectives, green-purple on eyepieces, purple on prisms. Intensive reflections from prisms. Medium intensity of coatings. 4/5.0
Warranty [years] 10 4.5/6.0
Final result
70.2%
119.3 / 170 pkt
Econo result 0pkt.

Summary


Pros:
  • handy and solid casing,
  • good correction of chromatic aberration,
  • low astigmatism,
  • very low brightness loss on the edge of the field.

Cons:
  • too narrow field of view,
  • objective lenses smaller than declared,
  • damp patches on one of the prisms,
  • truncated exit pupils.


After an excellent performance of the Kowa BD 8x32 XD Prominar in our test, our expectations concerning the 8x56 instrument were high indeed. Unfortunately the binoculars disappointed us. I don’t mean here the narrow field of view because we had been aware of its size before the test, after looking at the specifications. The problem is that it would be difficult to call the BD XD Prominar models a series; they rather constitute a group of devices loosely connected with each other, sharing hardly more than the common name.

Let’s consult the facts. On the one hand the same armour and colors were used in all of them; on the other hand, though, the 8x32 and the 8x56 models differ quite significantly when it comes to their constructions. For example an individual focusing mechanism is completely different: in the 8x56 you get a joystick on the central wheel which moves nothing outside and overall performs splendidly, in the 8x32 there is a simpler and cheaper mechanism which moves all the eyepiece. Although both these binoculars are quite small in their respective class the 8x56 model is clearly a low-budget device, featuring not only objectives smaller than declared but also noticeably truncated exit pupils which is most likely connected to too small prisms. The darkening of the interior of the tubes in the bigger model is also worse and probably it was done differently; as a result the areas near exit pupils are definitely lighter.


Kowa BD 8x56 XD Prominar, Steiner Ranger Xtreme 8x56 and Nikon Monarch 5 8x56


Add to that slip-ups hard to forgive in the 8x56 class of night instruments, where every photon counts. It’s sad that the Kowa loses light in many places. The transmission is perhaps not so bad but also hardly impressive for a night pair of binoculars – just several percent more and our assessment would be far more favourable. The real size of the objective lenses is officially smaller than stated in specifications by less than one millimeter but, according to our calculation, the light losses connected to that flaw are on a level of 3%. Another 3% disappears because of the truncated right exit pupil. Many a pickle makes a mickle…

Even good results in such categories as astigmatism, chromatic aberration or the brightness loss on the edge of the field don’t make us as happy as they should. With such a narrow field of view it is not difficult to correct off-axis aberrations properly. By the way this pair of binoculars doesn’t impress us with the distortion correction or the resolution on the edge of the field and it should.

It would be difficult to call the score of the Kowa 8x56 bad – it is a decent set of binoculars. Still next to the 8x32 model which might be easily treated as a price bargain and a very good deal, it looks completely bland. Pity…


Attention! In this test the transmission value has been measured only for two wavelengths: 532 nm (green) and 657 nm (red) with a margin of error never exceeding 1%. Four measurements have been taken for each optical path and the results have been averaged out.