with a 90 degree FOV (such as oculus) you are looking at the feed from 4 go pros at any moment. the hero 3+ does 4K, so you're reducing four 4K feeds into a single 1080p/2 (oculus DK2) feed.

When you're going from 33 megapixels to 1 megapixel, i'm not sure how much optics is going to matter...