well he got the dof part rite....
to flyingmuffyn:
a BIGGER f-stop number, like 16-22, results in a SMALLER aperture hole, which creates a GREATER DOF but lets LESS LIGHT in, so u have to INCREASE shutter speed or bump up ISO to compensate.
and vice versa...
so considering u wanted a shallow depth of field, which can be seen in the pic u posted, u would have already used a very big aperture (or small f-stop). Since it's still underexposed, the only other way would be to either use a higher ISO or increase exposure time (slow down shutter speed)...
AND
zoom won't have any effect on the amount of light... and don't blame the kit lens. it's not that bad.. really.. ur dof is just so shallow, that u are blurring everything that is just in front/behind ur plane of focus.. that's y it seems so bad.. u need to stop down ur lens when u shoot...