I'm planning on mounting my Canon 70-200mm ii lens on a 5d mark 3 but will not be able to use the tripod mount on my rig as it would slide too far back when it it shoulder mounted, thus colliding with my Zacuto Shoulder Pad.

Is the mount on the 5d Mark 3 strong enough to take the stress of this lens without the mounted tripod support? If not, does anyone have any recommendations for a lens support? The baseplate I am using is this one: DSLR Baseplate (http://store.zacuto.com/dslr-baseplate/)

I use my 70-200 all the time without lens support on my 5D. Maybe I've been lucky. It's better to mount on the tripod mount on the lens, but you don't have to. It certainly balances better as a still camera using the lens based tripod mount.

This is kind of old but I use the 70-200 f4 IS with a 1,4x extender without the tripod mount all the time without any problems.

The Canon EF 70-200 f2.8 L IS II USM is heavier than the 70-200 f4 IS version. The EF mount is strong. However, even a small vibration in front of the lens will ruin the footage due to the combination of weight and length of the lens and less weight of the camera.

If you mount the camera, due to the weight and length of the lens, there would be more pressure on the camera mount.

I use this lens with often a 2xII TC and mount with the collar while shooting with 1D Mark IV. However, with the C300 I mount the camera on the tripod and place the lens on it, free without any rigs. Same is the case with the 100-400 lens.

I have got the 5D III recently to act as another backup camera. It is small and the weight is also less. So I will mount the lens and then place the camera on it.

For still shooters, who know RRS, this is one interesting plate for mounting camera and long lenses: Kennan Ward Super-Tele Package - KennanWardPkg - Kit Configuration Page (http://reallyrightstuff.com/ProductDesc.aspx?code=KennanWardPkg&type=3&eq=&desc=Kennan-Ward-Super-Tele-Pac)

One can make slight variations as well