when i use the automatic focusing feature on the camera, it focuses. but if i zoom in some more i notice that the image is still a bit blurry so i focus again and then zooms out to my original composition. is this the right technique? or should i just stick to the original 'focused' image? does this happen because its supposed to happen or is it because of problems with the lens/body? i am using the cheap 28-80mm that comes with the body.