I got a rare pair of binoculars on Abbe-Koenig prisms – Eyeskey Zenith 10×42 for testing. The use of such prisms, compared to binoculars on Schmidt-Pechan prisms, should provide higher light transmission due to fewer reflections. The manufacturer claims a flat field without distortion and field curvature (FLAT FIELD). The 10×42 format itself (10x – magnification, 42 mm – lens diameter) is universal – for both daytime and astronomical observations.
EQUIPMENT
The binoculars are supplied in a cardboard box.
Inside:
-binoculars
-bag
-bag strap
-neck strap (measured width 44 mm)
-cloth for wiping optics
-lens caps (installed on the binoculars)
-double eyepiece cap (installed on the binoculars).
-instructions
BODY, MECHANICS, OPTICS
The binocular body is covered with soft rough rubber on the outside. The binoculars are quite massive, 915 grams with covers. The length of the binoculars with covers is 180 mm, without covers 175 mm – noticeably more than 10×42 binoculars on Schmidt-Pechan prisms. Width – 136 mm, height 53 mm. Tubes with a diameter of 53.6 mm. There are two holes on the sides for a neck strap. On the left half there is an inscription “Eyeskey Optics”, in the upper part there is an inscription “ED”. Under the bridge on the right half there is a serial number.
The focusing drum is metal, ribbed, with a diameter of 33.6 mm. Focusing to infinity is counterclockwise, the full rotation angle is approximately 480 degrees. At +5 degrees, focusing is tight. The measured minimum focusing distance is 150 cm. The measured range of interpupillary distance is 57.5-76 mm, the shift of the halves of the binoculars is tight.
Diopter correction is achieved by turning the ribbed ring on the right eyepiece.
The eyecups are metal on the inside and rubber on the outside, with a diameter of 41.4 mm. There are several locking positions (shift by 3.5 mm, 6.5 mm, 9.8 mm). In glasses with twisted eyecups, the entire field of view is visible, the pupil removal is comfortable.
The measured aperture is 41.97 mm, the lenses are recessed approximately 8-10 mm from the front edge of the binoculars. The objective and prisms are coated.
The eye lenses are 21.65 mm in diameter, convex, and the measured field of view is approximately 60.3 degrees. The eyepiece lenses are coated.
At the front of the binoculars, under a cylindrical metal cap, there is a socket for a tripod adapter with a 1/4 inch thread.
Ergonomics, of course, are not like those of the “open bridge”, but the binoculars are quite convenient to use. Some discomfort may be caused by the plug for the tripod adapter, it protrudes noticeably from the body.
TESTING
The light test showed that the binoculars hardly distort the color rendition, only a very slight yellowness, imperceptible to the eye, but recorded by the camera. Very good!
Polarizing filter test, the prisms have a phase-correcting coating, and the halves of the field of view darken almost simultaneously – this is good.
The exit pupils are round. There is a thin light ring around the exit pupil. There is a small light leak on the side, but it is outside the main exit pupil and does not interfere with observations.
The measured magnification is 10.16x
The binoculars have excellent collimation, and the eyes do not get tired at all during observations.
No channel desynchronization was detected, there are no delays when refocusing in either direction, and constant adjustment of the diopters in the right eyepiece is not required.
The image on the axis is very sharp, bright and contrasty. Longitudinal chromatic aberration is not noticeable, but photographically it is clearly visible as a bluish coloring of dark roofs near bright walls. Lateral chromatic aberration is small, well-corrected. Unfortunately, despite the declared Flat Field technology, there is a noticeable curvature of the field, and the image blurs towards the edge. The curvature of the field is noticeably stronger than that of the Eyeskey Infinity 8×50 binoculars. Astigmatism is well-corrected.
Straight lines are not curved. Due to the large ocular field of view, immersion in the picture is good.
The star test confirmed the excellent collimation of the binoculars. The stars in the central area are very clear, pinpoint-like. Towards the edge of the field of view (starting from the distance between the center and the edge), the field curvature begins to appear, and at the edge, the star is noticeably out of focus. When refocusing, the view of the star at the edge noticeably improves, but it is no longer possible to see the stars in the center due to the defocus.
SUMMARY
+ bright, sharp
+ excellent color rendering
+ good mechanics
+ fully coated
+ comfortable eye relief
+ distortion corrected (straight lines do not bend)
— significant curvature of the field
— the binocular body is noticeably longer and more massive than that of 10×42 binoculars on Schmidt-Pechan prisms
— the plug for the tripod adapter sticks out noticeably from the body.
I liked the Eyeskey 10×42 Zenith binoculars for their color rendering and image brightness, so if you don’t need full field flattening, it would be a good choice.