I have a friend who's requesting to have shots made for his LinkedIn profile where he's being photographed at the Mount Auburn Cemetery under the shade of trees. What kind of lighting and modifiers do I need to get a good exposure @ ISO 400 and f/2.8 in AP mode?
It really depends on the angle of the sun at the time you take your photos and how much of the background is in the shade and how much is in direct sunlight. Anything from a small reflector to powerful studio strength flashes might be needed for fill light. To use f/2.8 at ISO 400 you're probably going to need some sort of neutral density filter unless you are shooting right around dawn or dusk.
Your friend probably wants pictures leaning back on the tree trunk, but it can be deep shade back in there (and green light, icky). Your best light will be out under the edge of the tree drip line, in the shade, but inviting open shade instead of deep shade. Maybe try some his way, but at minimum, try some of it the better way.