hello everyone! I have recently began at a new job where I have to take pictures of people at parties to post on the internet. They are pretty normal pictures in terms of composition and content. I take them at f3.5 and depending on the light 20 to 40 Av with flash. The problems I am having is with the focusing of the camera, a lot of the times it doesn't focus right, i think it's because it's too dark. Other times the lighting doesn't look too good. I use a Canon XTi with the flash and lens it came with. What kind of flash and lens would you recommend for this kind of job? Do you recommend any other accessories? or any other kind of technique?