I found the performance on iPhone4 is very low, the camera screen is not smooth enough and become choppy. While the same app running on iPad2 is very smooth, also very good on Samsung Galaxy 2.
After searching the forum, it seems it is a old problem. I am using the latest Vuforia 2.0 SDK and Unity 3.5.6f4.
Do I need to tweak something in order to improve the performance? Or it is the problem of the iPhone4?