hello! i dont know how to fix my focus on 18-55mm lens. before when i focused on something in foreground and them moved camer little a side, it keeped focus on that something in foreground. but now when i do this, my focus jumps from one thing to enother, it start to focus on anything that's right at the center. when i attache 90-300mm lens it works right as it supose to wotk. but then when i attache 18-55 lens again, it starts to jump. can i fix it or i have to get a new 18-55 lens.