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The Celestron Nature Series Binoculars is pretty diverse with three Porro Prism Designs and two Roof Prisms and like Celestron's top of the range Granites, all the Nature Series binoculars apart from the 8x30 Porro Prism model have an open frame design that looks great, is comfortable to hold and gives you an excellent grip even with one hand.
As you will see from the specification table above, the 20×80 SkyMasters give you a greater Angle of View (3.2°) compared to that of the 27×70 SkyMasters (2.7°) Celestron SkyMaster Pro ED binoculars are the ideal choice for amateur astronomers or anyone who observes at great distances. The SkyMaster Pro ED uses superior optics, coatings, internal parts, and housing materials. With large objective lenses, BaK-4 prisms, ED glass, and fully multi-coated optics utilizing Celestron’s proprietary XLT coating technology, the view through a SkyMaster Pro ED sets the standard for astronomy binoculars.The Zhumell Tachyon 25x100 and the Celestron SkyMaster 25x100 on the other hand also have 4mm exit pupils (100 ÷ 25 = 4) and you still get the added reach and image detail with the 25x magnification. However the huge trade off is the increased cost, size and weight (se table above).
on the other hand, will give you 25 times the magnification of the object viewed by the naked eye, and achieves this with front lenses that are 70 millimeters in diameter. All six models in the series are of a roof prism design, using very good quality BaK-4 glass. The optics are fully multi-coated and protected in a fully sealed and waterproof Polycarbonate body that is filled with nitrogen gas to prevent fogging of the lenses. Lastly, it’s important to note that these binoculars are also water-resistant, making them suitable for unpredictable weather conditions. Specifications and PerformanceThe 25x70 version is one of the most popular models in the series. It offers serious large aperture light gathering in an affordable and reasonably lightweight configuration.
The eyecups and the eye-relief for me were also not the greatest. This combined with a small exit-pupil meant that I was often searching to get the full view, trying to get rid of the dark rings around the edges. I think better quality twist-up eyecups set at the correct amount of eye-relief would really help in this area.
Product Details
Depending on the product, Celestron offer either a 2 year or a very comprehensive No fault Lifetime Warranty on their entire range of binoculars. To give you an idea of how these dimensions compare, I have included the dimensions of a few fairly average full size 42mm bins and that of a few other giants in the table below: Custom-designed rubber armor and a durable chassis protect your SkyMaster Pro ED binocular from damage without weighing you down. Viewing through SkyMaster Pro ED binoculars is comfortable for eyeglass and non-eyeglass wearers alike, thanks to the retractable eyecups and nearly 16mm of eye relief. Eyeglass wearers can see the entire field of view while looking through the eyepiece with their glasses by twisting the eyecups down. For those who do not wear eyeglasses, the eyecups position the user’s eye behind the eyepieces at the correct distance for optimal viewing.
Moreover, their multi-purpose nature makes them an ideal choice for both astronomical and terrestrial viewing.Otherwise, the optics are the same as the Granite series, with many high-end features that include Dielectric Coatings on the Phase Corrected roof prisms. Porro prisms are arranged in a certain way with the benefit of providing greater depths of field and wider field of views compared to other “Roof Prism” equivalents. Magnification and Light Gathering Ability Most binoculars are either roof or porro prism designs, but there is also a third option: Reverse Porro Prism. This design is used for small compact binoculars where the eyepieces are more widely spaced than the main optics. The prisms are actually reversed so that the light path is altered for this configuration. Both BK-7 and BAK-4 refer to the glass used in a binocular's prisms. The terms were coined by Schott AG, an old and very-well respected glass manufacturer in Germany. BK-7, which is the less expensive of the two, is made with Borosilicate Crown glass, and BAK-4 is made with Barium Crown glass, which has a higher reflective index.There are other differences in BK-7 and BAK-4 prisms besides the glass type. BK-7 can have a less-rounded exit pupil than BAK-4 prisms do, and can cause vignetting of the far edges of an image, especially when using wide angle binoculars with a smaller exit pupil in low-light conditions. BAK-4, on the other hand, produces a round exit pupil that will allow you to see the entire field of view regardless of the lighting conditions. Most models have a wide field of view in relation to their power and the 8x42 Granite boasts one that is 426ft wide at 1,000 yards which combined with a stunning view and all the other quality features and components helped them scoop the Best Birding Binocular for 2012 award.
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