Originally posted by camera_nut
For lens reviews, Christopher Frost. But he doesn't review Pentax or Nikon. Mostly Canon and Sony.
Christopher's lens reviews are excellent. The systems he covers are Canon, Sony, and Fuji, but he also covers lenses from the independent manufacturers, including many that are available in Pentax K-mount (Samyang and Irix in particular). His reviews are always interesting, and the "Weird Lens Reviews" that he posts on occasion (covering truly oddball items past & present) are quite entertaining.
If you need additional videos to check out, I have an extensive list of links on my web site, covering about 17 different YouTube photography channels, as well as many links to videos about individual photographers:
Videos - Jay Alan Richardson Photography