ZIEL Stone Power 8×40 WW Binoculars Review

Good morning everyone, today I will tell you about a pair of Porro prism binoculars in a price range similar to that of smaller format binoculars. These are the Ziel Stone Power 8×40 WW which costs the public 138 euros and has a ten-year warranty.

I'm posting the video review below. However, you won't be able to subscribe to my channel this way. You can, however, by clicking on this link.Thank you all for your cooperation! 

 

 

 

MECHANICS AND FOCUSING SYSTEM

These binoculars are made of Bk-7 glass Porro prisms. The 8×40 format is a good compromise between brightness, depth of field, and universal use. The body is made of aluminum alloy, and it has an 8.2° field of view, equal to 143 m at 1000 m and a full 64° of apparent field. These binoculars can therefore be defined as wide-angle. The declared minimum focusing distance, however, is 5 meters, with an eye relief of 18.3 mm. My electronic scale estimated a weight with the small strap at 720 grams. They also have a thread for attaching them to photographic tripods.

The focus is central and external; the carriage that moves the two eyepieces translates. The central dioptric adjustment is 4 diopters, while that on the right eyepiece is +/- 3. As always, I tested whether the minimum focusing distance was identical to the stated one and found that it can focus at 2.7 meters. From this distance, you need to rotate the knob counterclockwise a little more than one turn to reach infinity. From 5 meters, however, you need to rotate the knob about 3/4 of a turn. The focus is smooth; it's a bit long, as you may have guessed, but there's no sticking or binding.

OPTICS

GOALS

They are achromatic lenses with a simple UV anti-reflection treatment (Multi Coated), given the price it is not treated on every surface, in any case, thanks also to the Porro prisms, the sharpness on axis is good, the contrast is lower than the X-Pro series which however is more expensive.

The color tone is slightly warm, which does not hurt to slightly increase the perception of low-contrast objects.

EYEPIECES

They're comfortable and wide-angle. The rubber lens hoods are retractable and soft, and the viewing comfort is excellent. At my 65 mm interpupillary distance, the distance between the eyepieces is 22.40 mm, so I can insert my nose without any particular problems.

 

PRISMS

The exit pupil of the Ziel Stone Power 8×40 WW It is circular with some vignetting on the outer edges, a feature that is due to the Bk7 glass prisms. The brightness of the binoculars seemed average for this price range. Reflections near the exit pupil are also quite low. Stray light at the edges is present and can be improved somewhat by trying to align the eyes with the exit pupils. Considering that this is an entry-level model with Bk7 prisms and only multi-coated optical surfaces, not all, this is a fairly average performance.

 

ABERRATIONS

ON-AXIS CHROMATIC ABERRATION

Porro prisms always do a great job. The reduction of chromatic aberration in the center of the field is excellent, sometimes only evident in very poor lighting conditions, but I have seen binoculars with roof prisms costing twice as much to be less correct in this area.

 LATERAL CHROMATIC ABERRATION

It is perceived as a faint purple-green halo starting from approximately 76-80% of the field of view.

FIELD CURVATURE

Obviously, given the purchase price it does not use aspherical eyepieces, for this reason the field is not completely flat, the degradation begins, proportionally, starting from approximately the 75-80% from the center of the field of view.

ANGULAR DISTORTION

Present in cushion, of approximately 5-6% towards 70% of the field of view

OTHER ABERRATIONS IN ASTRONOMICAL USE

I have highlighted that the presence of coma and astigmatism at the edges of the field, makes these binoculars not optimized for astronomical observations.

PRACTICAL OBSERVATION

In this price range, I usually prefer small 30mm Porro prism binoculars in 6x30 and 8x30 formats. However, there are some particular observing conditions, such as this evening on this lookout, where a little more light will be needed. Aside from the anti-reflection coating, the 40mm aperture is equally noticeable compared to an 8x30 of similar construction and quality, but obviously it can't compete with a top-of-the-line €2,000 model. Even the field of view, although not fully corrected to the edge of the field, is useful for having a broad overview of the area you're observing, especially without having to shell out too much money or if you prefer to spend it on a night vision or thermal imaging device, which will be more useful in the hours that follow. Keep in mind that the Ziel Stone Power 8×40 WW It costs as much as two cases of top-of-the-line binoculars or a tripod mount from a well-known brand. I appreciated it more for medium-distance nature observation, even near twilight, rather than for birdwatching, where I prefer faster focusing. Thanks to the excellent three-dimensionality provided by the Porro prisms, it is also useful for panoramic observation and is suitable for some brief astronomical observations, despite the lack of a flat field up to the edge.

PROS AND CONS

MERITS

• Format that lends itself to many uses
• Ten-year warranty
• Excellent eyepiece comfort
• Good finishing
• Brighter than a classic 8×30 of the same cost
• Possibility to try it in hundreds of optical centers scattered throughout Italy

 

DEFECTS

• It does not have a multi-layer anti-reflective coating
• It has a somewhat long focus distance for the professional birdwatcher
• It is obviously not as bright as the 42mm diameter Ziel X-Pro series

IN SUMMARY

The Ziel Stone Power 8×40 WW Among the dozens of options in this price range, this seemed like an interesting product. The quality of the finish and the collimation of the tested model demonstrated good quality control. Within the limits of its optical train and the quality of its components, it is suitable for even twilight sessions, and the apparent field of view allows for good detail perception without the classic "keyhole" effect often seen in products in this price range.

PRICE AND WARRANTY 

It costs 138 euros VAT included and benefits from a ten-year warranty

 

THANKS

I thank, as always, Marco Masat of Ziel for making the binoculars I tested available and for allowing me to share my impressions without restriction.