Svbony company has kindly provided me with several eyepieces for testing. One of them – SV190 18mm 1.25″ Ultra Flat Field Eyepiece FMC. A flat field (no curvature), a large eye relief (20 mm) and a field of view of 65 degrees are declared. Interesting!

The focal length of 18 mm is one of my favorites, as it is especially in demand with “fast” telescopes (f\5…f\6) when observing deep space objects (galaxies, nebulae, clusters). With “slow” telescopes (f\8…f\12), the eyepiece can be used for observing the Moon and bright compact objects in deep space.

The manufacturer  declared the following characteristics:

Model	SV190
Focal length	18mm
Size	1.25″
Eye Relief	20mm
Lens Structure	8-Elements/5Groups
Field of View	65-Degrees
Coatings	Fully Multi-Coated
1.25” thread size	M28.5*0.6
Thread specification under the eyecup	M42*0.75
Eye Cup type	rubber
Field diaphragm	23.4mm

Measured characteristics:

Weight with caps – 217.7 g
Weight without caps – 208.7 g
Weight per box – 317 g
Eyepiece diameter – 49 mm

Eyepiece length with caps – 84.8 mm
Without caps – 80.24 mm
Skirt length – 31.75 mm
Skirt thread diameter – 27.82 mm

Field lens diameter – 21.56 mm (concave, recessed by 8.92 mm)

Removal of the pupil from the glass – 21.94 mm
Eyecup height – 10 mm (when folded, it protrudes by 2 mm)

Eye lens diameter – 27 mm (concave, recessed 4 mm in the center)
Thread diameter under the eyecup – 41.86 mm

Measured field of view – 61 ± 0.5 °

To measure the dimensions, an ADA instruments Mechanic 150 Pro digital caliper was used, weight – digital scale of 500 g, and the eyepiece field of view –  Dioptra app.

The eyepiece is delivered in a sturdy cardboard box. The eyepiece itself is still in bubbled polyethylene and in an additional bag.
The set includes: the eyepiece, two caps and a cleaning cloth. Everything arrived quickly, safe and sound.

The eyepiece is quite large and weighty, weight with caps is 217.7 grams, and the diameter of the eyepiece in the thickest part is 49 mm. The body of the eyepiece is metal, except for the eyecup and ribbed tape in the center of the body. The eyepiece is made of high quality, without defects, there is no dust or fingerprints on the lenses.

The eyecup is rubber, it can be rolled up (for observers with glasses), or removed altogether. The material of the eyecup itself is very easily soiled, dust quickly adheres to it. For some reason, there is a T-thread under the eyecup – does anyone else use an eyepiece projection for astrophotography?

There is a filter thread on the eyepiece skirt. The field lens is concave, recessed by 8.92 mm, the inner diameter of the clamping ring is 21.56 mm. The skirt is cylindrical, without groove. The field diaphragm is not available for measurements without disassembling the eyepiece.

The eye lens is large, 27 mm in diameter, concave, recessed by 4 mm in the center relative to the eyepiece body. The edge of the diaphragm is blurred. The measured eye relief from the glass is 21.94 mm, but due to the recessed eye lens and the collapsed eyecup protrusion (+2 mm), I recommend that eyecup observers remove the eyecup completely.

The length of the eyecup is small (10 mm), when observing without glasses, you cannot press the eye and fix the position of the head – part of the field of view falls out. Perhaps this was done for the more compact size of the folded eyecup. An adjustable eyecup with rotation would be better suited here.

All optical surfaces bordering on air are coated. From lenses – green and yellowish reflections, from glues lens – dull colorless.

Svbony SV190 18mm 1.25 “Ultra Flat Field Eyepiece FMC Moon Test
Telescope – Newton 150 mm f\5 Sky-Watcher BKP150750 on Levenhuk ATZ mount.
The image is bright, almost everything is visible in the field of vision, but to observe with glasses you need to roll up or remove the eyecup.
A slight barrel-shaped distortion is noticeable (the moon is slightly flattened at the edge of the field of view), the image quality is good across the field.
No bright annoying parasitic glare was noticed.
When trying to look at the edge of the field of view, you must move the eye, otherwise the image disappears. The eyepiece is also picky about centering the pupil.
A slight curvature of the field is noticeable.
When compared with an eyepiece Nagler 17 тип 4 (17 мм, 82 градуса, 2″) the Svbony eyepiece showed better field sharpness and contrast, but a smaller field of view.
An Honor 8 Pro smartphone was used to shoot the moon.

Arcturus Test
Good sharpness on the axis. Towards the edge, bright stars turn into arrows (towards the center). The edge of the diaphragm is blurred.
Most of the field of view with good quality.
The eyepiece is combined with the Barlow lens flawlessly, there are no artifacts.

Summary
+ Good image quality on axis and in field
+ Works great with a fast telescope
+ Large eye relief
– The field of view is slightly less than stated
– The eyecup is too short.
I really liked the eyepiece, and so much so that I wanted it to be in my collection. Recommend!
You can buy the eyepiece in the official Svbony store on Aliexpress.

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