Pulmonologists become fairly good semi-professional chest radiologists simply by showing up, paying attention and working hard during their training, and making an effort to keep learning throughout their careers. We have the advantage over radiologists of actually being able to "clinically correlate" the findings with what's really going on, and to integrate that into our understanding of what we see on films. Still, specialized chest radiologists will always be the best (I believe) at quickly and intuitively recognizing pure radiographic patterns--they may review as many studies in a day as you see in a month, no matter how busy or diligent you are.