If I am doing a depth of field shot I manually focus on the part of the shot I want in focus. I always level the horizon on my pictures unless the tilted horizon is the specific effect I am looking for. I generally don't lose much of the desired part of the picture, which is an artifact of the 18-55 standard lens on my camera. If I shoot at 18 I almost get more picture than I want so the losses in leveling don't matter. My camera is 24 mp and shoots 6000x4000 pixel pictures which gives me lots of cropping room while still maintaining a reasonable pixel count for the resulting picture.