Thanks jfk
I will take a look but your talking a budget that would make a national museum wince.
I will see if I can hire them in Barcelona Spain where the show is but Im guessing that these things are not so easy to find.
In terms of projection overlap have you never noticed that the blacks are never black and when they overlap they create overlap highlights. This is the case on all overlapping projections except the most high end laser projections.
If you are showing in a lit public space then nobody will notice but not in a dark Gallery where it looks very amateur. Perfectly aligned projectors simply means there is no gap or seam , (and no keying either).
I have done it like this many times and looks perfect.