The Svbony company sent me a pre-production sample of an interesting zoom eyepiece with a focal length range of 8-20 mm for testing. The field of view of the eyepiece is declared to be from 72 to 57 degrees. On high-aperture telescopes (f/5) it can be used as a universal telescope for observing deep sky objects. On telescopes with a small aperture (f/10), the eyepiece is suitable for observing the Moon, planets, and bright deep-sky objects (globular clusters, small planetary nebulae).
APPEARANCE AND MEASUREMENTS
The eyepiece is supplied in a white cardboard box. Inside there is a case for storing the eyepiece and, in fact, the eyepiece itself with two covers.
The eyepiece is large and massive. The length of the eyepiece with covers is 140 mm, the largest diameter is 60 mm, weight is 460 grams. A huge eye lens with a diameter of 32 mm, under the soft folding eyecup there is an M43 thread. The field lens size is 23 mm. The front of the eyepiece has a thread for a 1.25-inch filter. The lenses are clean, no dust was detected in the field of view. The focal length adjustment mechanism is tight, there are no locking clicks. The scale shows focal lengths in 1-millimeter increments – in fact, 13 eyepieces in one. The eye relief is large, but to observe with glasses, the eyecup must be folded or removed altogether.
Measured field of view (using Dioptra app):
8 mm – 75.2°
14 mm – 63.1°
20 mm – 54.8°
The field of view was 8 mm larger than stated, and 20 mm less than stated.
TESTING
To check the eyepiece, a Sky-Watcher BKP150750 telescope (parabolic Newton, aperture 150 mm, focal length 750 mm, f/5) was used.
20 mm: noticeable vignetting at the edges, the edge of the aperture is not very clear, a little dark. The image of stars is distorted towards the edges, but the image quality is good across the field. Slight field curvature.
8 mm: significantly increased field of view, sharper aperture edge. From center to edge, image quality is very good. Towards the edge the star stretches into a small comet.
Aberration correction up to the 12mm focal length is good. After 12 mm, aberration correction worsens. On slower instruments (f/7-f/12), the image quality across the field should be even higher. I also checked the eyepiece on the large Sky-Watcher Dob 14″ SynScan Go-To telescope – the zoom mechanism turned out to be very convenient for quickly selecting the optimal magnification for various objects in the Messier and NGC catalogs.
The eyepiece is parfocal; refocusing when changing focal length is not required.
Some filters screw on normally, but some begin to wobble when fully screwed in – perhaps there is something wrong with the thread on the eyepiece skirt.
SUMMARY
An interesting zoom eyepiece with a very large field of view and well-corrected aberrations (especially in the range of 8-12 mm). The disadvantages include the tight zoom mechanism, as well as the problem with installing some filters. I hope that these problems will be eliminated in production samples.