There are many zoom binoculars out there, most are poor. These are without doubt the best I have ever used, zoom binoculars are usually a trade off as when zooming the field of view decreases, alarmingly in most case. These hold up really well, I suspect Swift made sure to make their zoom as good as it could be due to their reputation for quality.

JB22 (Itabashi Kogaku Kikai Seisakujo Inc, Tokyo. JE29