How to make that cool pictures where the subject of interest appears sharp and everything else is blurry?
One of the most attractive effects of photography is the so called bokeh, which is really easy to make once you know the theory beside it. Do not confuse with the “defocus” stuff, when you deliberately (or not) place the subject out of focus. For example when you take a close portrait with the Holga and you forgot to unset the landscape option of the lens.
Let me introduce the “depth of field” concept (from Wikipedia: http://en.wikipedia.org/wiki/Depth_of_field ):
“The depth of field (DOF) is the portion of a scene that appears sharp in the image”
Basically, the DOF is determined by the lens f-number. Lowering the aperture (increasing the f-number) increases the DOF, this results in a sharp image from the closest subject to the infinite. Just set a small aperture (f16 or f22), focus on your subject and almost everything will appear sharp in the picture, nice thing for landscapes.
Then, increasing the lens aperture diameter (lowering the f-number) decreases the DOF. So, once you manually focus your lens over the subject of interest, the portion of the scene that appears sharp will be really small, sometimes only few centimeters in front of the focus point and behind it (see the picture of the chess table).
Now you could understand that not all cameras will do the work, you would need to play with the aperture and focus. Single lens reflex (Zenit), Twin lens reflex (Seagull, Rolley) or rangefinder (Fed, Zorky) cameras are the best players coupled with a luminous lens (f2 or lower).