I've been studying writing for several years, and I feel fairly confident in my ability to write a novel. Before I take the plunge and go for it though, I was curious about a slightly different path: screenwriting.
I've never really looked into screenwriting at all, but as I get closer to talking to publishers, I've found myself thinking that screenwriting might be a better option. From my limited research, it seems that screenwriters make quite a bit more money than novel writers (unless you're wildly successful I suppose). The main thing for me though would be the fact that (assuming you are any good) your audience will probably be bigger. I have no evidence for this, but it's my assumption that in general, more people watch movies/TV shows than they read books, in this day.
As a result I'm wondering how hard it would be to transition from novel writing to screenwriting. They are obviously very different, but they both have the same story principles at the core (as far as I know). How hard is it to transition from novel writing to screen writing? A detail of what I would have to learn/do would be appreciated.
Note: I'm open to opinions following the lines of 'you should never screenwrite!' or 'you should never novel write!' or something similar. However, please back these up with reasons (your own opinions are fine), and please put them in a comment. If you put them in an answer, please make sure you answer the question first.
Further Note: This question is not a duplicate of this or this. Both of those questions deal more with the differences between screenwriting and novel writing, and not actually transitioning from one to the other.