Binoculars review
Kowa 10x42 BD42-10
Kowa is a Japanese manufacturer with a very well-known, although modest, offer. Its main part consists of BD42 models, with the 42 mm objective lenses and the magnification of 8 and 10x, aimed chiefly at ornithologists. As the producer guarantees, the binoculars are designed to be the lightest and the most handy with observing a high optics quality at the same time. Their construction is based on the roof prisms in the Schmidt- Pechan system made of BaK-4 glass and phase correction coated. One of the Pechan prism’s edges doesn’t give the full reflection so it must be covered by an additional reflective layer. Kowa used a specially designed C3 coating there to minimize the light losses to only 1%. This result is by several percent better (at the extreme ends of the visible spectrum even more than 10% better) than in the case of conventionally used aluminum coatings.
The binoculars, tested here, are waterproof and nitrogen-filled.
| Magnification | Lens diameter | Angular field of view | Prisms | Eye relief | Weight | Price |
|---|---|---|---|---|---|---|
| 10x | 42mm | 105/1000(6o) | BaK-4/roof | 17.6 mm | 745g | 1988PLN |
Results of the review
| Real front lens diameter |
Left: 42.02+/-
0.05mm Right: 41.99+/- 0.05mm |
8/8.0 | ||||
|---|---|---|---|---|---|---|
| Real magnification | 9.8+/- 0.2x | 3/3.0 | ||||
| Transmission | 87+/- 3% | 12/15.0 | ||||
| Chromatic aberration | In the centre on the border between medium and low; at the edge - low. | 6.5/10.0 | ||||
| Astigmatism | Slight. | 7.3/10.0 | ||||
| Distortion | The distance of the first curved line from the field centre compared to the field of vision radius : 67% +\- 7% | 8/10.0 | ||||
| Coma | Low even at the very edge. | 8.5/10.0 | ||||
| Blurring at the edge of the FOV | The blur occurs in the distance of 74% +\- 3% from the field of view centre. | 4/10.0 | ||||
| Darkening at the edge the FOV | Slight. | 4/5.0 | ||||
| Whiteness of the image | Almost perfect. | 4.2/5.0 | ||||
| Collimation | Perfect. | 5/5.0 | ||||
| Internal reflections |
|
3.6/5.0 | ||||
| Housing | Very comfortable, ergonomic and stylish. Handy. Regulated eyecups. Nitorgen filled. The rubber near the objectives sticks out minimally. | 7.7/8.0 | ||||
| Focusing | Very comfortable central screw. Comfortable rubber ring on the right eyepiece. The focusing is made inside. | 4.8/5.0 | ||||
| Tripod | There is a comfortable exit. | 3/3.0 | ||||
| Interpupilary distance | from 58 to 74.1mm | 5/6.0 | ||||
| Closest focusing distance | 1.7 m. | 2/2.0 | ||||
| Eyepieces FOV | Apparent field of view of 60.4 degrees. | 7/10.0 | ||||
| Field of view | Measured by us amounted to 6.01 +\- 0.03 degrees and was in perfect accordance with the specifications. | 5/8.0 | ||||
| Quality of the interior of the barrels | Dark and matt inner tube which near the prisms becomes ribbed and shiny. Clean. | 4.3/5.0 | ||||
| Vignetting |
OL: 1.7%, OR: 2.9%. |
5.5/8.0 | ||||
| Prisms quality | High quality BaK-4. | 8/8.0 | ||||
| Antireflection coatings | Greenish on objectives, prisms and eyepieces. Medium intensity | 4.5/5.0 | ||||
| Warranty [years] | 2 | 2/6.0 | ||||
| Final result | 15th place in the overall ranking of the 10x42 binoculars test | 132.9/170
78.2% |
||||
| Econo result | 12th place in the econo ranking of the 10x42 binoculars test | 6.8pkt. |
Summary
Pros:- very solid and stylish casing,
- high quality of prisms and coatings,
- low distortion,
- excellent coma correction,
- slight astigmatism,
- chromatic aberration quite well-controlled,
- low brightness loss at the edge of the field,
- sharp image already from 1.7 metres,
- good blackening inside.
Cons:
- truncated pupils,
- short guarantee period for this price class,
- the image at the edge of the field could have been sharper.
Once again it is proven that if a given manufacturer has rich tradition when it comes to the optics production and the factories, producing its equipment, are near, it can demand a lot and have good results. In the case of Kowa it resulted in a polished-up, sophisticated product which is difficult to flaw. Very good optical properties, stylish and solid housing - those things make you keen on buying. You can carp at truncated pupils, which shouldn’t look this way in a 700 USD class device, and a short guarantee period in our country. In this class of equipment a 5-10 years of guarantee is an absolute minimum to compete successfully on the market. It is enough to look at the Olympus EXWP-I and the Vortex Viper, which cost 100 USD less and, having a score very much alike, come with a 25-year-long or even lifetime warranty. If only the tested Kowa had the same warranty period, it would improve the test score by 3-4 points and it would equal the best competitors.
