Resizing an image should not have any effect on the "true" focus of the image. What you are most likely displeased with is the "pixelation" of the lower resolution of the resized image. When you resize the image to a smaller pixel array, it has to try to give you the same amount of information on fewer pixels. When you take the smaller resized image and enlarge it (zoom), you will start to see the square pixels, just a nature of the beast and is why the camera companies keep coming out with bigger and bigger "megapixel" ccd chips for their cameras. So most likely you are running into the file size versus image resolution wall.