What kind of texture? Swirl? From the sound of it, the paint has just "sunk", or been absorbed more in some areas than others. That happened with our ceiling, previously painted and with one coat of primer for the latest job. I assume the ceiling was clean and not heavilly stained? I would get a shorter nap roller.
1/2" is pretty much like using a rag mop. Let the paint dry well, use shorter roller and do the "W" thing when you roll on the paint - paint a "W" shape on about 3x3' area and then straight same direction and then straight across it. With a 1/2" roller it seems you would have an extremely heavy coat in some areas; if heavy enough, the lap marks probably won't go away. Flat paint?