You don't need to focus at infinity. You need to focus on the distant objects, then use a depth of field table to help ensure that what you need to be in focus actually is. There is a hyperfocal distance that is combination of settings and distances that provides the greatest depth of field, but you should take that as a suggestion, and with a grain of salt. For critical work, cut the ranges suggested in half.

For instance, the www.dofmaster.com calculator suggests that with your camera, at a focal length of 24mm, at F8, the hyperfocal distance is 11.9 ft. If you focus at that distance, everything from half that distance, or 6 ft to infinity will be in focus. Now it is important to understand that the really distant stuff will not be nearly as crisp and sharp as what is at 12 ft, and your results at 6 ft will not be quite as sharp either, but it will be "acceptable." You would get better results if you stayed exactly where you were, and close the lens down to F11. The calculator suggests that the hyperfocal is 8.43 ft, with 4.2 ft to infinity in focus. Focusing at 11.9 ft the table suggests that everything from 4.93 to infinity will be in focus, so you are within the limits of acceptability.

http://www.dofmaster.com/dofjs.html

This is a great resource - and a whole lot better than just "googleing" it as has been suggested. Good luck with this.