In my experience, it's always been hard to find a well matched pair of zoom lenses for a stereo shoot. The Optimo 15-40's and 16-42's are very popular for 3D because they're a useful focal range for this application and they're also quite light and compact. For that reason, they can also be a little hard to come by because they're a fantastic Steadicam lens so they often live on episodic productions for months on end. These lenses despite their useful range hardly ever track through their zoom though and by that I mean maintain the same optical center from their widest side to their longest side. This can be tested by putting up center crosshairs on the video output or LCD viewfinder of the camera. Next make a big "+" sign on the wall about 15-20' from camera. On the wide side of the lens put the crosshairs on top of the +, lock the sticks. Now without touching anything else, zoom in all the way. If at the end of the range the crosshair is still lined up over the +, you have a zoom lens that is optically centered. More likely what you will see though is the + gradually drift away from the crosshairs as you zoom in. Either a lot or a little bit of tracking error is quite common in all zoom lenses and is hardly noticeable for 2D applications. However in 3D, lenses need to be as closely matched as possible and a change in focal length on lenses that don't track inevitably means the cameras will need to be re-aligned to one another. The Optimo zooms in the hands of a skilled lens technician can be made to track to one another within the margin of error but this is always a time consuming task that I have yet to see completed successfully during an equipment checkout for a 3D shoot.
Enter the Panavision PCZ 19-90mm T2.8
Not only are these the ideal focal range for 3D but they're also pretty fast at T2.8. And like all Panavision products, built like a naval destroyer. These are the only zoom lenses I've ever encountered that track almost perfectly throughout their entire range, have minimal breathing, and also make beautifully rich and contrasty images with gorgeous focal fall-off. For S3D, these are the lenses to get if you're able to get them but like all Panavision glass, the demand far exceeds the supply.
Check out this Beast Master -
The Genesis cameras are an intimidating size on their own but take this pile of hardware, motors, and electronics, put it in the ET Quasar Rig and you've got something that looks more like a Transformer than a camera. More than meets the eye! Nerd.