Image Render Speed issuse

Support Basics & Interface
1

i have a large blender file/model, and I am making images of portions of the model, when I render an image the image comes up reasonably quickly however the 3d window is inactive. i figure the rest of the model is being rendered. :-?

Is this normal? Can something be done so that only what the camera sees is rendered, thus reducing the time?
:expressionless:

2

Additionally, I have a camera pointing at the subject that I would like to render, ortho set to off, and when I set Ortho on the contents of the view disappears when viewed from the camera view.