iPhone/iPad Viewport issues

[oida]

I have been trying to get into responsive design recently. The only problem I have come across so far is the viewport stuff on the iPad and iPhone.When I set the Initial-Scale to 1 it seems to double the page size on the iPhone (retina) even if the media query is set to width 640px. Note that the media queries are working fine as far as I can see, everything adjusts as it should. I can fix the double zooming problem by either double tapping to zoom out every time the page loads or by setting the initial-scale to 0.5. The problem with setting it to 0.5 is that when you view it on the iPad it's half the size of the screen. 1.0 seems to work on the iPad but seems to double it up on the iPad (The iPad and iPhone have separate media queries).Summary: Scale 1.0 on the iPhone doubles the page zoom, fine on iPad. Scale 0.5 fine on iPhone, half the size on the iPad.Anyone know what I might be doing wrong?Thanks