Did a research in Wikipedia about DOF. I'm not really familiar with photography stuff and my camera is only a point and shoot so there is no way of knowing it. (unless you read about it) I see these f-numbers on the render settings dialog box but do not know how to use them. That all changed this afternoon when I read the Wikipedia article and did some renderings. The thing is, I learned using the technique using a virtual camera inside Indigo Renderer.
The maple tree on the scenes was a revision of the 3d maple tree I was working on last week. The notable change was on the form of the leaves and their arrangement. The leaves are now curving in two directions. Their positions on the twigs had been re-arranged in a way that those on the tips would be a bit smaller and do not block the leaves behind them. This model is included in the 3d tree collection in the 3d warehouse.