.5x would technically mean 1/2 the standard image zoom of a flat lense, or 2x the image u can see and .3x is usaully the lowest wideangle/fisheys go, or the most it exagerates the image.
for example the widest lense you can buy is the century optics mk1 death .3x lens, but my wideangle raynox mx3k whihc is .3x is not as wide so it depends on the lense it self.
.5x is not very wide...