Prism binoculars with a magnification of up to 7x represent a separate class of devices. These are compact binoculars with a large field of view and a limited use. Of the fairly well-known models, I can recall offhand soviet БПЦШ 6×30, Bushnell 4×30 Xtra-wide, VisionKing 5×25, Kowa 6×30, Pentax Papilio 6.5×21. How can such “kids” be useful for astronomy lovers? Firstly, the study of constellations. With low-magnification binoculars, one can easily identify faint stars in the constellation, pave the “star track” to search for a nebula or galaxy, and due to the small magnification, shaking hands is almost imperceptible, which greatly increases the convenience of observation and the limited visible magnitude of the binoculars. Well, of course, the observation of wide star fields and the brightest areas of the Milky Way personally gives me great aesthetic pleasure.
Recently on sale I noticed an interesting model – Veber Prima 5×20. It interested me in a small magnification, a sufficiently large exit pupil (4 mm), long eye relief 16.2 mm, and also the declared coating of all optical surfaces. This is a small prism binoculars reverse Porro system. Unlike the roof- and classic Porro binoculars, the reversing binoculars have less distance between the lenses than the interpupillary distance of the eyes. This leads to reduced stereoplasticity (volume) of the image. In some cases, this can even be useful – for example, in a theater, or when observing nearby objects (<1 m). In addition, binoculars with a reduced stereo base are very compact.
A small introduction. The exit pupil of an optical device is a small circle at the exit from the eyepiece in which all the light collected by the lens is concentrated. To calculate the size of the exit pupil, it is enough to divide the diameter of the binocular lens by increasing. For example, with 8×56 binoculars it is 7 mm, and with 10×25 binoculars – 2.5 mm. The larger the exit pupil, the brighter the image at dusk and at night. As a rule, for daytime observations, a pupil of about 3 mm is sufficient, and for astronomical observations, preferably from 4 mm and more. At night, the human pupil expands to 6-8 mm, so in binoculars usually the value of the exit pupil does not exceed 7 mm, otherwise the light at the exit of the eyepiece will go past the pupil. Binoculars, in which the exit pupil is 6-7 mm, are called PUPIL EQUAL. When this is achieved the maximum brightness of the image. If you compare 8×56 and 8×30 binoculars in the night sky, then the image brightness in binoculars 8×30 will be 3.5 times less, since with the same magnification the lens of 8×30 binoculars is 3.5 times smaller in area, and, accordingly, less light falls into the observer’s pupil.
For a long time I looked at the pupil equal binoculars. I was not impressed with the low-end models (Nikon Aculon 7×50, ZOMZ 7×50, Yukon Point 8×56), so for the time being I was using Nikon Sporter EX 8×42 binoculars. However, it was possible at a reasonable price to get used binoculars with DDoptics Nachtfalke Ergo 8×56 gen II roof glasses (hereinafter DDoptics 8×56). Initially, there was little information on this binocular, but after the purchase I found quite a few reviews of this binocular, produced under other brands. Apparently, the binoculars turned out successful, since it began to be sold immediately in various reincarnations. In general, I will not pull, proceed to the review.
Binoculars with a formula of 10×50 are among the most popular.Such binoculars are suitable for both terrestrial and astronomical observations.In my opinion, 10x is the limit for comfortable observation without using a tripod. “The Pentax Russia” company kindly provided me with an interesting Pentax SP 10×50 WP binoculars for testing.The binoculars are quite new, the announcement took place in January 2015.
Pentax SP 10×50 WP
Specifications are stated:
Binoculars with central focusing and “porro” prisms
2 elements in 1 group
3 elements in 2 groups (aspherical element declared)
Real front lens diameter
Field of view from 1000 m
Exit pupil diameter
Field of view
Diopter adjustment range
+/- 2 D
From 5.5 m to infinity
Retractable with fixation
Waterproof when immersed to a depth of 1 m (JIS protection class 6, is not suitable for use under water), nitrogen content of the housing.
“Tripod adapter N” (69553)
Fully multicoating of all optical elements. Hydrophobic lens coating.