Generally, background blur (bokeh) is a function of focal length and aperture. The longer the focal length, the larger the aperture (smaller f number) will give you more bokeh, or a shallow depth of field.
- an image shot at f1.4 will give more bokeh then one shot with f8
- a 85mm lens will give more bokeh then one shot with a 35mm lens
Some portrait shooters love the 85mm f1.4 lens, some prefer the 105mmf2.8. Some use the 70-200 f2.8. All these lenses have large apertures and long focal lengths. The bokeh with these lenses is outstanding.
If you are using a digital prosumer camera, I suppose the amount of bokeh you can get is limited. This is because of the very short physical focal length of digital cameras. Even largish apertures from the G series Canons and Olympus cams may at best give adequate bokeh, probably not enough for pure subject isolation. As many post above has suggested, shoot at max telephoto wide open.
Try also, to focus nearer the foreground, with the subject just at end of the area of focus. I dont know if you get what I mean. Lets say the image is sharp from 2m-10m when you focus at 4m away, place the subject somewhere around the 8m mark.
That is true. You can also use the Gaussian blur tool in PS to create the shallow DOF for the pictures. Then use the history brush tool to unblur the subject. However, you cannot create the nice bokeh effect on PS (correct me if I am wrong)
with a maximum focal length of 50mm and a aperture of f3.5 . You can get adequate bokeh if the focusing distance is close. But with an angle of view of a 200mm, close focusing will result in a very tight composition.