Received a Svbony 3-8 Zoom yesterday and took it out for a daytime spin today as well as did some bench test measures. Been inactive for more than a year as nothing really new or interesting in the marketplace IMO. But this little zoom, especially for under $150 USD caught my eye as it has what I feel is a perfect focal length range to be a one eyepiece show for planetary. Used my Vixen 81S
1. External build quite nice. Good fit and finish.
2. Zooming is not too tight or loose, so just right amount of friction. The "feel" of the mechanism as it zooms is just a bit rough, so not buttery smooth. Will probably work itself smooth over time. Nothing bad, just could feel the internals working to move the zoom.[/list]
3. Rubber eye guard easily comes off so nice. Otherwise, at 8mm setting my face was just lightly touching to top of the eye guard when observing. At 3mm setting had to press in a little to see the entire
4.
5. Eyepiece is parfocal throughout the zoom range
6. Field Stop visually remains sharp at all settings.
7. No perceivable Field Curvature from center to edge across the zoom range.
8. Slight vignetting of the
9. Determined this by observing an out of focus airy disk pattern and could see the circle get truncated by a little less than a half as it reached the field stop. Only happened again at the 7-8mm settings. Given that it needed to be almost at the field stop do not think this will show any dimming in the field at night, but need to do a night time test to verify. Similarly, the out of focus airy disk stayed perfectly round when in or out of focus near the field stop so does not appear to have any astigmatism present. For note, the airy disk view was using the sun reflecting off a convex surface on a car in the distance.
10. Rectillinear distortion was very well controlled, much better than in any modern Plossl I have tested. Virtually nonexistent at the 7-8mm setting, slight at the 5-6mm setting, and approaching something less that what I would call moderate at the 3-4mm setting (probably on par with the TV DeLite if memory serves).
11. Image contrast appeared quite good, but a daytime test cannot mimic IME contrast performance for planetary observing, so will reserve judgement until a good planetary test, but expect it will probably turn out to be perfectly acceptable if not better.
Quite impressed with this little eyepiece so far, but night time is where the rubber hits the road of course. And it is affordable as well! The focal length range is IMO perfect for all planetary observing needs, so nice to finally have a single eyepiece brought to market that can serve the typical range of planetary magnification needs. Examples: in 10"
Happy New Year!
-Bill (1/2023)