image slightly out of focus during pan

I need to animate a still image by panning across it.  If the Frame Size in the Sequence Settings is 1920 x 1080, and the image itself is 1080 px high, then as long as the image is in sharp focus, is there any reason why it will become slightly out of focus during the pan?  As soon as the pan ends, and before it begins, the still image is very sharp.  I'd like it to stay that way during the pan too. Thanks.