Clamp orbit camera rotation

Hello,
Working on mobile, I want to move the camera using touch slide and pinch around a target. For now everything is working well, I can move the camera around the object and zoom in or out. there is the code used to move the cam around:

Code (CSharp):

1. //touchMagnitude is touch position delta, get the angle rotation over axis
2.       Quaternion camTurn = Quaternion.AngleAxis(touchMagnitude.x, Vector3.up);
3.       Quaternion camTurnHeight = Quaternion.AngleAxis(touchMagnitude.y, Vector3.zero + transform.right);
4.  
5.       Quaternion rotation = camTurn * camTurnHeight;
6.  
7. // add the rotation to the offset between the camera and the target
8.       cameraOffset = rotation * cameraOffset;
9.  
10.       transform.position = target.position + cameraOffset;

What I want to do now is to clamp the camera deplacement in height, because when the camera go over the gameobject it have a weird deplacement behaviour.
And there it's going bad...
I've tryed two options :
1) limit the quaternion rotation, to not be over a value, so : How to clamp a quaternion ? if we talk in degrees, I want to clamp the x rotation between -80 and 80.
2) check the angle made by the camera looking to the target, to not move height if the angle is equal to 80°.

I've tryed everything about this two options so if somebody can give a way to reach what I looking for, it will save my week.