He has in fact looked at the F-1 firing footage, and he claims the dark appearance of the plume means they were not really firing at appropriate capacity. Of course Percy doesn't realize, or else doesn't acknowledge, that he's seeing footage from DACs mounted on the MLP and running at something like 200 fps. That limits your exposure. He wants to compare the plume to still photos taken from afar.

Clearly David Percy knows nothing significant about the physics of rocket propulsion. He is still at the point of claiming the LM descent engine must have been firing at 10,000 lbf because they wouldn't have specified a more powerful engine than necessary. He can't seem to do the computations necessary to show that you hover on 2,800 lbf or so, and that you simply can't hover at 10,000 lbf.

Both he and Bill Kaysing seem to think 10,000 lbf is some whopping huge engine. The V2 produced something like 160,000 lbf, and even most jet engines produce more than that.