It depends on how long the 1/2" section is. Until you exceed the flow rate of the 1/2" line, there won't be any excessive friction, and both the volume and pressure may not be affected. FWIW, even a soda straw, with no flow, would have the same pressure, but obviously the volume you could get from it would be different than, say, from a fire hose. What happens when you have a restriction is that the liquid speeds up (think venturi, a jet in a carburetor is an example as is a hose nozzle), then, it can slow back down again if it transitions to a larger pipe. There is a maximum safe velocity of water flow in pipes, and about 5-6fps is the max you want, otherwise, it can create turbulence and pipe erosion.
All pipe creates friction as liquids flow through them - the higher the flow rate, the more friction loss.