AJ Henderson and Craig have excellent answers. I'd just like to add my own knowledge about making miniatures look full-size. As far as I can tell, there are 4 factors that make a miniature look, well, miniature.
1) Lighting. If the train is supposed to look like it's outside, shoot it outside or next to a window that sun is coming through. Sunlight looks way different than indoor light because of color and the fact that it's one really bright light and a bunch of "ambient" light from the rest of the bright sky.
2) "Thickness" of the air. If you look at faraway mountains or buildings or trees, they're always a little "hazy", a little less colorful, than things next to you. So if a real train is 1/2 mile away, it will also appear a little bit hazy. A model train, which is probably a foot away or less, won't be hazy at all. The artists who did special effects on movies used to up a scrim (a tranparent but hazy sheet) in between the camera and the model to add fake haziness. It looked more "real" on film.
3) Details. A real train has tiny, tiny details like bolts and screws. A model train won't have anything that tiny -- they would be nearly microscopic!! But the person watching the film / video will notice that they're missing, so the model will look more like a model.
4) "Depth of field". That's a photograph/film term that has to do with what is in focus: things that are close, things that are far away, or both. When you focus on something even 10 feet away, everything behind it is (usually) in focus. That's called having a big depth of field. If you focus on something 1 foot away, everything behind it is (usually) out of focus. That means the depth of field is small. If you're focusing on the nearby model, and so you have a small depth of field, most people viewing the film/video will notice that and it will look like a miniature. One way around that is to have a fake background just a few feet away, behind the model, so it will still be in focus.