Bokeh is the subjective quality of the foreground and background out of focus areas.
Shallow depth of field on the other hand depends on many things.
1) The nearer the subject is to the camera on any given focal length the shallower the depth of field (dof).
2) A wider angle lens will have greater depth of field than a longer focal length. So in a zoom even if the f-stop doesn't change say at f2.8 - the wide end of the zoom will have greater depth of field than the tele end of the zoom.
3) Sensor size/ film size - the smaller the sensor/film size the greater the depth of field. So a medium format camera at a given focal length of lens will have a shallower depth of field than say a FF/35mm film camera at the same lens focal length.
Note: Focal length and field of view are not the same thing but are related. A standard 50mm lens on a 35mm/FF DSLR will have the same field of view as a 90mm lens on a medium format camera.
on a 4/3 sensor the depth of field doubles (as the field of view also doubles). ie a 25mm lens on 4/3 sensor have the field of view of a 50mm lens on FF and if shot at say f2.8 the depth of field will be equivalent to f4 because it's actually a 25mm lens in FF terms but the depth of field remains that of a 25mm lens. Makes sense no?
So 2 50mm f.14 lenses used on a FF DSLR at a given f-stop will have the same about of background and foreground blur but the quality of the bokeh will probably be different!
1. bokeh is ≠ out of focus areas
2. the amount of out of focus area is dependent on a) sensor size, b) focal length and c) f-stop used
a lot of things play a role in getting shallow depth of field:
(1) sensor size, the larger the sensor size, the shallower the depth of field, all other things being equal (i.e. equivalent focal length, aperture)
(2) focal length, the longer the focal length, the shallower the depth of field, all other things being equal.
(3) aperture, the larger the aperture (or the smaller the f-stop), the shallower the dof, all other things being equal.
(4) subject relative to background distance, if you move the subject closer while keeping the background at same distance, or if you move the background further, while keeping the subject at the same position, all other things being equal, bg will be thrown out of focus more.
(4) is the reason why you can get bokeh for macro and closeups but not for portraits.
but (1) is the driving reason why you are limited in the first place.
If i may suggest, try this method. Use manual mode or aperture priority mode, then slide the knob to MANUAL FOCUS MF. after which with aperture 2.0. choose the thing u want to take a picture of and then you manually change the focus till you get a sharp image on the object. When I did this, I got a really nice bokeh. Try it!
Try to zoom the object and take picture again. max zoom with max aperture will work well.
if you want to use wide angle with nice bokeh, then the object must be very close to camera and background must be very far.