Kowa 8x42 BD42-8
The 8x42 BD-42-8 model, tested here by us, belongs to a group of binoculars produced still in Japan. That series consists of devices with the following parameters: 8x25, 10x25, 8x32, 10x32, 8x42 and 10x42. As the company claims, these binoculars were designed in such a way so they are physically the lightest and the most handy, while their high-quality optics remains intact. Their construction is based on Schmidt-Pechan roof prisms, made of BaK-4 glass, with phase correction coatings. One edge of the Pechan prism doesn’t ensure you a complete reflection so it must be covered by an additional reflection layer. Kowa used a highly reflective C3 coating which reduces the losses of light to just 1%. That result is by several percent better (at both ends of the visible spectrum even by over 10% better) than in the case of standard aluminum coatings.
The binoculars are waterproof, nitrogen-filled and they come with a two-year warranty period.
- solidly made, stylish casing,
- low astigmatism,
- sensibly corrected coma,
- slight light fall-off on the edge of the field of view,
- good quality prisms made of BaK-4 glass,
- clean and dark inside the tubes.
- narrow field of view,
- noticeably truncated exit pupils,
- weak distortion correction,
- noticeable chromatic aberration on the edge of the field of view.
Although our test result of the Kowa 8x42 is good, the overtone of our summary won’t be positive. That Japanese company decided to use a narrow field of view. We can understand their reasons but not without difficulty. If the field is so narrow you should get something else instead. For example you can expect the field which is corrected perfectly well till the very edge. Here there is no such thing, though. Quite the opposite in fact.
The distortion is corrected weakly, the chromatic aberration on the same edge of the field as well. You see neither good, high resolution, kept to the very end of the field, nor a perfect coma correction. Additionally there are significantly truncated exit pupils and an average transmission function graph (presented below). Faults like these we could accept in the case a roof prism instrument for ~150 Euro but from a Japanese piece of equipment costing almost 500 Euro we expect much more – certainly not a transmission level of 82-85% in the centre of the visible spectrum.
The Kowa BD 10x42 model fared very well in our tests. The field of view of eyepieces was sufficiently wide so the pair of binoculars could boast of a significant field, reaching 6 degrees. What’s interesting, that field was corrected as well as in the 8x42 model. We encouraged the purchase of the Kowa 10x42 but if you want to buy the Kowa 8x42 we advise you to think that decision over seriously. You can find several better options at such a price.
Pentax 8x43 ED DCF and Kowa 8x42 BD42-8