Television & Movies

So I have been watching over the air broadcasts lately and mostly reruns of shows. I was amazed at how high a resolution the original star trek was but I remember there was a thing where it was revamped although I thought that was just special effects. then I noticed many other old shoes like I dream of genie also have really great resolution. I noticed some newer shoes though had worse resolution. Heck star trek the next generation seems worse. I have been wondering if this is because of trasition to digital filming. Like the old film I assume might have greater clarity when digitized but when we started filiming in digital maybe it was worse. I could see tv shows doing it first because they figure the resolution going out only had to be so good for the sets of the day. Anyone know about this type of stuff?