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.

Declared and measured characteristics:

Magnification	5
Aperture, mm	20 (meashured – 20.5)
Coating	FMC
Exit pupil, mm	4 (meashured – 4 mm)
Eye relief, mm	16.2 (meashured – 16 mm)
Visible field of view, degrees	10.3 (meashured – 10.5)
Interpupillary distance adjustment, mm	55 — 74 (meashured – 55-74)
Linear field of view (at 1000 m), m	180
Close focusing distance, m	1
Type of binoculars	Center Focused
Prisms	Porro, BaK4
Fog and dust proof	No
Eyecups	twist up
Sizes, mm	86х109х48
Weight, g	265 (measured – with eye covers 255 g)

I was able to buy used Veber Prima 5×20 binoculars in excellent condition almost completely (binoculars, eyepiece covers, case, cleaning cloth). There wasn’t just a lanyard strap. In my opinion, a neck strap will be more convenient. The binoculars are made in China. There it is also sold under the brand name Larrex 5×20, marking LR-CB05. In foreign online stores it is also under the brands Kenko and Lacerta.

Housing.
The binoculars are very compact, actually fits in the palm of your hand. The case is made of rough plastic. Inside, a metal cast frame is visible. The device is very light, weighing 255 grams with eyepiece covers. Hard rubber eyecups, twisted out, without intermediate fixed positions. There is no thread for the tripod. Because of the small case, you have to use an unusual grip – the fingers of one hand on top of the fingers of the other hand, or by clutching your fingers into a “lock”.

Ribbed plastic focusing drum, diameter 22 mm. Focusing is a little tight, no play. When focusing, the binocular lenses simultaneously shift along the optical axis. The full rotation range is approximately 3.5 turns. A total of 12 divisions on the drum. For my vision (-1.5) it was required to rotate the drum 2 divisions (60 degrees). The focus reserve for nearsighted is 15 divisions, that is, up to about -11 diopters.

The right lens is 1-2 mm closer to the end of the binoculars than the left. The lenses are recessed into the body, so the risk of getting them dirty with your fingers is minimal. The binoculars can focus on close objects, the minimum focusing distance is about 1 meter.

On the right eyepiece there is a ribbed ring for diopter correction. When using it, the eyepiece shifts entirely along the optical axis. I have no complaints about the ergonomics of the binoculars, but personally I would not refuse to rubberize the case to improve the grip or several ribs. Ideally, something like the Pentax Papilio 8.5×21.

Optics.

The measured diameter of the lenses was 20.5 mm, which is slightly larger than the stated one. To my surprise, all surfaces were coated. Although this is stated by the manufacturer, very often in Chinese binoculars without coating some optical element appears – the inside of the lens, prism, etc. Fully coating provides good light transmission and high contrast. The lens has blue and green lightening, on the prisms it is green, bright yellow and blue, on the eyepieces it is green, blue. Not super, of course, but there is coating and it is already pleasing. There are several diaphragms inside the binoculars, however, gray “entrails” are also visible.

Eye lenses are large, with a diameter of 18 mm. The measured eye relief is about 16 mm; the entire field of view is visible in glasses. The measured field of view of the eyepieces is 48 degrees, the visible field of view of the stars is 10.5 degrees.

The exit pupils on the axis are round. No “squares” are visible – indeed, Bak4 prisms. Near the exit pupil there are places with spurious reflections

When examining the exit pupils of a small distance (20-25 cm) and when the binoculars are tilted, the shape of the exit pupil becomes like a cat’s eye, and when the eyepieces are tilted up, the area of the exit pupil decreases by about 10-15%, when tilted down – by 30-40% , when tilted left and right – by about 20%.

The change in the interpupillary distance is carried out by shifting and spreading the halves of the binoculars. The measured range is 55-74 mm.

Prisms are fixed on glue. In the lower part of the binoculars and under the focusing drum, adjustment screws are hidden behind the rubber pads. The binocular collimation is excellent, the eyes do not get tired even from long observations.

Image.

After the first look through the binoculars, I was a little sad – the lower edge of the field of vision was noticeably “blurred”. However, the sharpness on the axis, brightness and color rendering are very pleased. The stability of the picture was also impressive – shaking at 5x is almost not felt. A little later, testing binoculars on the stars, I found that the stars retain a completely satisfactory appearance only within the central third of the field of view. Further, the image slowly deteriorates and at the edge jumps out of focus. With refocusing, sharpness at the periphery improves, but eye accommodation is not enough for comfortable refocusing. In addition, the image is sharper in the upper region of the field of view than in the lower. The edge of the view is slightly uneven, with a thin blue border. Distortion becomes noticeable from the central third of the visual field.

I found an interesting effect – during the day, with the eyecups twisted out, I could not look to the left or right side of the field of view, because the pupil of the eye shifts from the optical axis and loses the exit pupil of the binoculars. To look left or right, you need to slightly shift the binoculars left or right, but personally it prevents me from doing the nose. Up and down you can watch without problems, slightly raising or lowering the binoculars. I encountered the same effect when observing with Nikon Aculon A211 8×42 binoculars. During twilight and night observations, the problem does not arise, since the pupils of the observer are already quite dilated and when the eyeballs rotate, light from the eyepieces enters the pupils.

During daytime observations, neutral color rendering was very pleased – binoculars practically do not distort colors. Glare on the lanterns and the moon is practically absent.

General impressions.
+ Compactness, light weight
+ large visible field of view
+ excellent sharpness on the axis
+ good color rendering
+ full optical illumination
+ good light transmission
+ large pupil projection

– sharpness at the edge of the field of view could be better
– uneven sharpness along the field
– lens caps are not provided
– poor light protection, parasitic reflections inside the binoculars

Summary. I liked the binoculars and become my constant “backpack” binoculars for constant use, as well as for travel. Due to the small magnification and high sharpness on the axis, excellent image stability and excellent detail are achieved. Watching the Milky Way and starfields in it is a pleasure. Yes, blurry stars on the periphery are a little upset, but in practice this is not too striking, especially if you focus on the central area of ​​the field of view. With this binoculars, Jupiter was found in the daytime sky when it was not far from the Moon. When observing under a dark sky, the binoculars easily showed the brightest objects of deep space – the nebula M 8, M 17, the galaxy M 31, and many open clusters in Sagittarius. I recommend Veber Prima 5×20 to buy for anyone who needs a lightweight, compact and inexpensive binoculars with a good picture and a small increase.

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