I don't use a tripod for taking photos of my paintings, but now I have some worries re ability for FAA to print!
I have found I need to take a photo in 100% natural light(no flash), so I always put my painting out flat on the outdoor patio, of course no sunlight hitting it, taken at fast enough shutter speed so that camera shake isn't a problem. For me, I've found f8 or around there works best. Then it requires editing in something like Lightroom to get the colors just right, or as close as possible as right to the actual painting.