I have a web camera (Logitech, Inc. HD Webcam C910) connected to my desktop computer. It has a Zoom control. This control worked in previous versions of guvcview (I am not sure exactly which ones), but is not displayed at all in guvcview-1.5.3. So it is not possible to zoom this camera anymore using guvcview.
media-tv/gtk-v4l-0.4 draws the control correctly, and it works as intended.
The bug does not exist in media-video/guvcview-1.6.1