My Christmas layout is 11' deep. I tried forced perspective one year using HO buildings in the rear. For ME it didn't work. I think for 2 reasons:
1. My eyes, in person, could easily tell they were just small non-O buildings, and,
2. Like was mentioned above, my track ran right by them and when the train was in the area it really looked dumb, bluntly speaking.
BUT.... and this is always something that I believed in: forced perspective looks great in pictures where your eyes are only seeing that 2D image. When 3D your eyes 'know'. As long as some of the advice given above is followed. Maybe on some of the gargantuan layouts that we see in print it could work in person, but on layouts like my smallish 11' deep one I don't think it works well in person
- walt
