huh? the different within these two f stops suppose to give you different in ranges that is infocus... I suppose, it is either u didn't meter the subject right, or you are using Manual mode having the shuttle speed not set correctly
DOF = the depth, or range of the in-focus area
small F stop (eg, 2.8) = Large appeture = shallow Depth of Field = only a small area is in focus
large F stop(eg, 16) = small appeture = wide depth of field = the whole picture in focus?... something like that...
Google a bit more on this, you'll find tons of details.
AMD, Can.... the results tend to be more marked when you zoom to the max.
If I'm not wrong, DOF can be affected by 2 things. First is the Aperture size. Like the others said, large aperture= more circles of confusion (is that the term?)=more isolated focus=shallower depth of field. for small aperture the results is opposite.
The other thing that affects the DOF is your lens. For e.g, if i took a portrait of someone close in using a wide fast lens, and then composed another frame with exactly the same composition & focus point, this time shooting with a tele lens from further away, the tele lens will give a much shallower DOF.
Like you said, on Av the pictures tend to be darker, so for me, normally i try to shoot manual and then use the Ev meter to gauge the exposure.
Depth of field = area of photograph which is in sharp focus. It's affected by 4 things:
a) Focal length
c) Size of the subject
d) Distance of camera and subject
Stopping down your aperture (eg f2.8 to f8), you gain deeper depth of field, ie more area is in sharp focus. Since you don't seem to want deeper depth of field, stick to large apertures. Going to longer focal lengths decrease depth of field. So you should stick to longer focal lengths.
Above handily regurgitated from the most excellent 'John Shaw's Nature Photography Field Guide'.
apart from your understanding of the words "depth of field", you got it man!
what you're looking for is called "shallow depth of field".
anyways, remember to switch to macro mode if you get too close to the subject :thumbsup: