Time to post some details of my present design.
Can you get access to 2 of these in Austria?http://www.amazon.com/DryLin%C2%AE-W...3804774&sr=8-2
You will need two to have 2 slider tables for each camera and a spare rail you can cut to smaller sizes.
Then order 3 of these dove tail quick release from Manfrotto. You will need one for each camera and one for the rail.http://www.amazon.com/Manfrotto-323-...3805006&sr=1-3
Other than your tripod, you now have the basic hardware to fabricate a good variable stereo base slide bench for very low cost.
You will need access to a drill press for precision drilling of some mounting holes to mount the quick release plates on the slide tables and a center hole to mount the quick release plate to the center of the rail. I made 3 different size rails for convenience. I have one that is 230mm, 660mm, and one that is full length from IGUS, about 1 meter long. Depending on your shooting needs and carrying convenience you will shoot stereo with either the short or middle length rail. The long full length rail is best reserved for true slide rail camera motion in 2D shooting that this IGUS rail system was originally designed to do.
What stereo base distances you select are arbitrary but based on a formula for using your intended stage, say a soccer field and game or a mountain range where you enter your distances and lens settings to determine the stereo base of the two cameras. The most important estimated distance, IMO, is the near object distance minimum that will be in the shot. If it is to be 100 meters away, your stereo base will be less than if it is 1000meters away. In other words, if I'm shooting a scene with a near object that comes into the shot 5 meters away and my stereo base is 500mm then the shot is ruined as the near object will not appear converged in the scene.
Your questions on alignment of the cameras with my bench design:
I align the release plate to the camcorders visually squaring them up as best I can and snug the 1/4-20 screw just tight enough to allow the camcorder to twist with a little force. This does not need to be tightened further as it will stay for a day's shooting.
The alignment is done by first leveling the rail. I like to carry a small straight line level to put on the IGUS rail to assist in this alignment but the bubble level on the pan head will do fine. Now set your cameras at maximum stereo base on the rails and go into the 2D menus for each and set up the camera settings. for auto focus iris and other as desired and according to the sync instructions of your two camera LANC device. On my Lanc Shepherd the adjustments are done on the master camera and the other slave syncs to it. Make sure your camcorder display info is on and you have a grid line on to use for calibration of camera alignment.
Start with the left camera zoomed out full wide and find an object in the center of your shooting stage you can lock in on. Position the camera left cross hairs on the screen as desired on that object. Now go to the right camera and look for that same object and align the camera by twisting it on it's plate mounting so that the two objects are lined up on the cross hairs. You now have the cameras coarsely aligned for full wide lens setting. This will be good enough and work for everything at full wide angle.
Now fine tune the alignment for zoomed in object in the same stage. This time you will set the left side of an object in the shot to the left cross hairs and then go to the right camera and position a distance to the right that matches the IA of the stereo base to the camera right cross hairs. The wider stereo base, the larger the stage and therefore the less critical this zoomed in alignment is.
Still these are just initial alignments of the physical cameras for shooting at great distances and close is good enough.
The final vertical disparity alignment and horizontal as well as other tweaks to the alignment is done in post using the 3D stereographic auto calibrate. Here the final results will end in perfection of the stereo illusion.
You need to do a good coarse calibration of the cameras but don't waste time trying to perfect this and don't worry over it. There is just a practical limit to what can be done when shooting great distances. Better to take the shot and land the bullet on the paper target, then later on adjust the bullet hole to the bullseye ( metaphorically speaking)
Once the coarse alignment is done at full wide stereo base, I have found that sliding to different stereo bases will hold the stereo base good enough and you can always do a quick check on the grid cross hairs to a reference object in the scene to be sure something didn't get bumped out of alignment. I have also removed one camera, switched it to 3D mode and did some shooting of close ups ( within 4 meters ) then switched back to 2D mode replaced the camera on the rail with the dovetail quick connect and it was still in alignment with the other camcorder. But having a third camera is a better idea. I have a third slider table for the rail from igus that I can roll video and take stills of the same scene that I can stick in the center of the twin cams. This is also good for rigging with the NEX5n I use for 3D super wide AR panoramas. The IGUS slider is really a versatile tool for all these applications.