First impression: It's huge! With seven big pieces of glass in four groups, the SV171 is a 'serious piece of kit’. What all that heft gets you is very good optics with very good eye relief.
It's twice as heavy as the lovely little Svbony 7-21mm zoom, but it weighs less than, say, an ASI1600 camera, so any good astrophotography mount will have no trouble handling it.
I went looking for optical problems but didn't find much. It's parfocal from end to end, and the eye relief is comfortable (spec says 19.5 to 16mm). I found only slight astigmatism (predictably a bit more on my ƒ/4 newt than my ƒ/10 refractor) but it wasn't enough to detect in either scope while observing the moon. Brightness, contrast, and color fringing are comparable and perhaps a little better than my Meade Series 4000 fixed focal length oculars. Using a building with lots of windows and railings about a mile away I didn't see any evidence of distortion, and when I panned across Jupiter with it at the edge of the field the planet didn't show any elongation.
Two minor complaints: the twist zoom is rather stiff and the large barrel makes tightening the eyepiece holder screws awkward. I assume the stiffness will improve with use, and I solved the screw problem by simply not inserting the eyepiece quite as far.
All in all, in my view, the Svbony 8-24 zoom is an excellent value thanks to very good quality and a remarkably low price.
I really like using it for star alignment even though it doesn't have cross hairs. At 24mm it's almost like a finder, and at 8mm--even with approximate centering—it makes syncing my mount reasonably precise. In fact, these new eyepieces are so good that I'm inclined to say that a zoom and a Barlow are all you need these days. Sure, if you're in the league of exceptional amateurs doing serious observing, that won't be true, but for hobby astronomers on a budget I think a case can be made.
(The data comes from the real experience of astronomers in cloudynights.com.)
Thanks for your reading.
Welcome to try and comment.
Can you use an adapter to covert the SV135 zoom lens 7-21 from 11/4" to 2" and get better viewing?