I am curious to know if the object is too small can I just change snapshot position?

Yes, that is the way to do it. If the object is small you want to move closer to the object. However, when changing the snapshot position you need to recalibrate the robot at that position. So I would say that the minimum field of view that you can go too will depend on the calibration grid you can use.

@Etienne_Samson on the support website there are some ‘must-dos’ when printing the calibration board to make sure they are the right size. If we want to lower the FoV of the camera to locate smaller object, can we calibrate with a smaller board? 

@Catherine_Bernier @Sebastien nope, you must always use the provided Grid either for UR3 or UR5/10. Do not scale them! You can find the grid inside the manual here: http://support.robotiq.com/display/RVS/4.+Snapshot+Position

They are also available directly on the website.

Remember that the snapshot position is can be different the the calibration position. In short, you can have a snapshot position to be close and get small parts ( minimum field of view is 10 x 7.5 cms) and then move back to do the calibration.