The professional way to align the focus at infiniti is to use an autocollimator. There are other ways of aligning the focus using a second SLR as a collimator which is decribed here or here.
--Tripod (optional)--Cardboard and Wax paper (or ground glass)
Steps (If you access to a piece of ground glass, you can skip step one.)
1. Wax paper can be used as a temporary substitute for ground glass. Cut a cardboard frame that will fit the base of the film gate. The cardboard provides some rigidity to the wax paper. Cut a piece of wax paper and tape it tightly against the frame.
2. The distance ring is attached through three small set screws. It is not the bigger screw which simply acts a stopping device when turning the focus ring. Unscrew the set screws and remove the distance ring. You can unscrew the front element all the way, but don't.
3. Mount the camera on a tripod. You'll need the camera to point at a faraway object. Place the camera in a shaded area and the subject to be bright so you can see the best. Out a window or and open door works well.
3. Open the back and tape the frame to the film gate.
4. Open the aperture to the widest setting. Open the shutter to "B" or "T".
5. Focus the lens. Use the jeweler's loupe to help determine best accuracy.
6. Replace the focusing ring and tighten the set screws.
Of course, if you have a piece of ground glass, it makes determining focus the easiest. This is a Hasselblad focusing screen