The Zoom option is only for magnifying the view on the screen. If you take an image at that point, the resulting image will reflect what resolution you have chosen, not what the screen shows. You can select a lower resolution in SharpCap which will define a smaller FOV, thus magnifying the image that is created.
These are the available resolutions for your camera:
1280X960@60FPS
1280X720@98FPS
1280X600@116FPS
1280X400@168FPS
960X960@74FPS
1024X768@90FPS
1024X400@160FPS
800X800@85FPS
800X640@106FPS
800X480@141FPS
640X480@133FPS
512X440@145FPS
512X400@158FPS
480X320@196FPS
320X240@254FPS
JohnD