Later, I have clicked on the camera and going to modify panel where is the multi pass effect I have selected enable button. then clicking on preview and going to render I made sure that viewport is camera. there it is easy to see how the changes were made. I have changed the position of the camera putting it on the teapot and then the depth of field changed as well, so now it is easy to see that the teapot looks clear as a main figure, and others are more as a back view.