These are three images from the NBTVA CD Number 1
When I finally got the disk locked and looked at the picture, I was afraid I had a defective disc with one hole misplaced. The problem instead was a tiny bit of dirt partially blocking the hole, undoubtedly picked up from my fingers when I was grabbing the disk to decelerate it and test the loop response.
I have temporarily installed a better diffuser for the LEDs, and the pictures are now quite respectable, as you can see here. There is some unevenness of brightness caused by the camera shutter speed.