A side note: I spent quite some time trying to optimise the output from the relay system by combining various optical items and spacers. The final configuration worked very well for HD video at least, producing crisp and clear footage.
Inserting a field lens into the relay might have improved rendition further because the relay optics could be stopped down more, but vignetting is always an issue in these setups. A general notice is that the only stopping down should occur at the front lens, in this case the 6 mm f/2.8 Fisheye, not on any of the relay optics. I mention this because it is a counter-intuitive principle to what most people would select, but the recommendation has a most reliable source (Brian Caldwell).