Barry Biediger on Forced Perspective
Barry wrote the following notes on forced perspective in response to a modeler who asked this site’s our advice about applying that technique in a box-in-progress. I thought it was well worth sharing with anyone considering playing with the technique.
I have tried to calculate the size of objects at certain distances for forced perspective scenes (here’s a size/distance calculator) and I’ve tried to do something similar to the vanishing point with strings solution some artists mention, but using triangles of foam-core. For some reason, I couldn't get the angles and sizes of things worked out using those methods. In my limited use of forced perspective, I found that just eyeballing it worked best for me. I sometimes start by printing out a photo of an object at scale, then deciding what distance you need to have between it and the viewing window—keeping in mind that you will need some distance between it and the back of the scene as well. Next, measure the size of the nearest part of the scene. Then, mock up the object at the distance it needs to be in the scene, and set your converging walls between the nearest part of the scene you measured and the object.
In my opinion, a bigger factor in selling the idea of forced perspective than exact distances and scales is limiting the viewing window so the viewer can't change their viewing angle much, since small changes in viewing angle will kill the forced-perspective illusion. If you need to have something like, say, foliage in the scene, keep in mind that you can have some larger, more defined leaves nearer the viewer and smaller, fuzzier leaves toward the back. This holds for any objects or groundwork in the scene.
However you approach it, any time spent mocking up the scene will pay off. Use styrofoam, foam core, Play-Doh, or whatever else is easy to work with to see to the scene will work how you want it to. The more you tweak, or even remake your mock-ups, the easier and faster the final modeling will be.