Miniature effect Nikon d3100?

I just got a Nikon d3100 and am interested in the miniature effect but I need some tips. For one thing, when I try to apply it to a pic I can only do it on a select portion of the pic. Is there a way to widen the box and select more at a time or can I save it then go back and add it again later or whatever? I need tips on how to use this effect please and thank you!

I take it you have not read the accompanying article that describes how the "miniature" effect is done.

If you are using a Nikon, you will need to buy a PC lens (perspective control). The problem is, those lenses are very expensive.

Here is a link to those lenses

http://www.nikonusa.com/...index.page

You can enhance the miniature effect with photoshop. Try this tutorial
http://www.tiltshiftphotography.net/