Someone recently asked me to post about viewfinders. Well, today I was reading my new landscape book (Carlson's Guide) and he says a viewfinder is good for beginners, but should be abandoned by more advanced artists. And while overall this seems like a great book, I couldn't disagree more about viewfinders. I think they are essential tools. You can decide what your composition will be before you start to sketch it out. You can measure and compare where things are in relation to the frame, which helps immensely with proportion. I never used one in college (add that to all the things they DIDN'T tell us) and can't imagine how I ever did so long without it. Keep in mind - your viewfinder should be the same proportions as your canvas/panel. There is an adjustable one available at most art stores called a Viewcatcher.