Bushnell Powerview 8x21
Bushnell Powerview 8x21 is part of the Powerview series, the entry level series from Bushnell. The viewers come with a variety of magnifications and have a sharp price/quality ratio. Depending on the type, the coatings of the glass are multi-coated or fully multi-coated. The lens coatings are designed to guide the light captured by the lens to the eye in the most efficient way. On the outside, almost all models have an extra rubber grip layer so you have (and keep) everything completely under control! In the middle is a convenient and easy-to-handle focus knob to get the sharpest possible view of your target. The viewers are provided with fold-down eyecups so you can use the viewer in no time even wearing glasses. Bushnell Powerview 8x21 is the lightweight among the lightweights
The Powerview series is available in a wide range of magnifications; if an object is farther away it is wise to select a high magnification; however in practice, a magnification of 8x or 10x is usually more than enough. These viewers have relatively small objective lenses, which makes them lightweight and compact in size. They are also easy to store and carry.
The twilight factor is calculated by multiplying the lens diameter and magnification. Then you need to take the square root of this figure (this is also indicated in our specifications). If you are in densely forested areas, or want to see animals that only appear during dusk (e.g. deer) it is wise to go for a viewer with a twilight factor of at least 15 (preferably higher). The twilight factor is also influenced by the coatings on the lens, the type of glass used and the coatings on the prisms. More expensive binoculars may have a lower twilight factor but usually give a much brighter picture than cheaper binoculars with a higher twilight factor.
Weight and dimensions
If you travel or go hiking a lot then compact binoculars are recommended. These are easy to carry and not so heavy on the neck, but a compact viewer has a smaller lens and therefore a lower twilight factor. Also, the field of view is much smaller when you go for a high magnification (higher than 9x)
Porro or roof prism viewer?
The Powerview series is available as porro binoculars and roof prism binoculars. Porro binoculars (see diagram below)are broader binoculars and based on the first design of binoculars. The Porro consists of two rectangular prisms attached together so that the light is reflected three times, and this results in an ultra correct image. The conventional binoculars use Porro Prisms.
A roof prism viewer uses a roof prism (see diagram below). This design is technically more complicated than a Porro prism design, because it uses prisms which must have very accurately polished edges. The light is reflected four times. This design is more compact, but because the path of light is longer and the prisms more complicated, the quality of the glass and the manufacturing must be of higher quality than that of the Porro Prism design. Only then can an equal performance be achieved. Roof Prism binoculars have straight tubes as shown in the picture.