There's an iPhone and Android app called Artemis that lets you pick your camera and lenses, and see what your frame would look like with the different lenses. It uses the phone's camera, so it's not accurate for DOF, but is gets really close for framing.
If you just want to see what fields of view you get at different focal lengths with different sized sensors, Abel Cine has an interactive webpage that shows that: http://www.abelcine.com/fov/
Just wondering but are you able to do this your self ( eg own camera and lenses)
Understanding what is going on in any comparison images you may find.. may mean you need to have more info than a sample might tell you. eg distance from camera/lens to subject, f/stop, sensor size etc....