Stereo calibration
I have been trying stereo calibration. I have taken chessboard images from two different cameras. The cameras are kept on a level table. Single calibration of the two cameras is correct I think because they're the same mobile model and the focal length results are similar. But I have a doubt about the stereo calibration results because my translation vector is non zero in all three directions with big values. But they are just kept on a level table, side by side. z component of the translation vector should be zero, right?
If you mean by "my translation vector is non zero in all three directions with big values" the transformation matrix between the two cameras, the z could be non zero but not with a big offset (there is always a slight difference when you position manually the two cameras).
Also, pay attention to the unit you used during the calibration (meter, centimeter, ...).
There is an example (stereo_calib.cpp) for openCV 3.0.