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Kowa has been a renowned Japanese optics producer since 1946. They know how to deal with production of good quality antireflection coatings. In case of the TSN-55N model you get multi-layers of course, that cover all air-to-glass surfaces. From the side of the objective lens these coatings shimmer with shades of green and purple; when it comes to the eyepiece there are even more colours.

Brightness and white balance of images provided by the Kowa are in accordance with standards you can expect from top-of-the-range instruments. It's worth adding that the bar is set very high - much higher than in case of a typical pair of binoculars. Apart from an objective lens with a focusing element and an inverting prism set you get also other parts like an angled prism and an zoom-type eyepiece which construction, with these angles of view and eye relief, must be complex. The number of glass where light can be absorbed, and the number of air-to-glass surfaces where you can catch unwanted reflections of light, is really high.

Despite these facts the brightness and colour renditions provided by the Kowa are beyond reproach. You don't get such a crystal-clear, white images like in Swarovski instruments, you can notice slight warming of colours, some shades of yellow and green, but it's a negligible effect, some might say even welcome.

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The exit pupil is round, without any truncations, no matter what magnification you employ. The area around it is relatively dark. Brighter, concentric rings that change their dimensions as you zoom in or out is the only thing you can carp about.

The fact that there is high quality fluorite glass in the objective lens makes our expectations concerning correction of chromatic aberration really high. The Kowa TSN-55N doesn't disappoint. In the centre of the field of view this aberration is very low and, what's interesting, decreases slightly with the increase of the magnification. A similar situation can be noticed on the edge of the field. At 17x chromatic aberration is low, at 25x it looks very much the same, and at 40x it decreases a bit. If I wanted to use a point scale from our binoculars tests I would grant 8-8.5 points out of 10 at 17x, and at 40x it would be 8.5-9 points. Such results are really splendid!

When it comes to the sharpness of images the situation is reversed – the lowest magnification is actually the best. In its case you get crystal-clear, sharp images practically to the very diaphragm. At higher magnifications you can notice some out-of-focus areas only near the very edge of the field but it's a rather small area; you can say the quality of 97-98% of the field is in full accordance with the highest standards that should be offered by top-of-the-range equipment. The diaphragm is distinctly cut off in the 17-25x range; only at 40x you can notice slight blurring.

Distortion control is on a good level – at 17 and 25x you see a slight pincushion variant, at 40x it turns into a minimal barrel. Overall it's not anything you should worry about.

The Kowa TSN-55A corrects coma splendidly well. Sensational results you get at the lowest magnifications, where point-like images of stars are preserved in the majority of the field. Some slight deformations are visible only in the last 5-10% of the field of view radius.

At higher magnifications coma makes itself felt a bit more but still Kowa deserves a very high note. This aberration appears only in a distance of 75-80% of the field of view radius and remains low next to the very diaphragm – a round of applause!

It's not easy to guarantee good astigmatism control of such a complex optical system but even in this area the Kowa doesn't disappoint. Here the middle of the range fares the best, and we would award it 8.5 points out of 10. A bit lower result, that of 8 points, we give the 17x magnification and the lowest, 7.5 points, goes to 40x.

As you see the Kowa TSN-55A managed to pass our tests without any slip-up in all the testing categories, with very good, or even excellent results.