How to Clean the camera contacts on a DSLR
When the camera has trouble auto focusing the first step to take is to clean the contacts on the lens. If it continues then the contacts on the camera may need cleaning. When you clean the contacts in the camera you have to be extremely careful because they are inside the shutter chamber and there are a lot of small parts that can be easily broken in there. Face the camera down at all times during the cleaning procedure. Take the battery out of the camera and remove the lens. Put the rear cap on the lens to keep it clean and the body cap on the camera. Take the body cap off and use a blower to blow air onto the contacts inside the camera. Then use a nylon fine brush to brush the contacts. Remember be very gentle. Put the body cap back on the camera. Dip a q-tip in isopropyl alcohol and squeeze the excess out of the q-tip with your fingers. Put a microfiber cloth over the tip of the q-tip and squeeze it so that the alcohol bleeds through the cloth. Take the body cap off and rub each of the individual contacts with the cloth covered q-tip. Put the body cap back on the camera. Next take the body cap off and use the dry end of the q-tip covered with a dry spot on the cloth to dry the contacts. This is the last step. Put the body cap back on the camera and let it sit for five minutes before putting the lens on again. This should help the auto focus work.