Thanks to everybody for the comments and tips. The pic attached was taken 2 weeks ago with the same ring light in AUTO and the setting was 1/180 F22 ISO 200. this week a try to take some photos of another patient, same settings, same ring flash and the result was pictures with no exposure at all (black). I went out side the office in a really sunny day at 4 pm to make a test with the settings in AUTO and the camera shows and ISO 200 with enough light to use an ISO 100. I am going to take all your advices and let all of you know.Thank you very much for your help, everybody.