Incredibly skittish birds, the Blue Tit; the minute you enter the garden they vanish. I overcame this by setting camera on tripod in garden, manually focussing to the fat-ball holder and remotely taking the photographs on my iPhone from the conservatory.
This was the most that 'dined' at the same time, though a dozen or so were flitting around the tree.
@cottiac They are so nervous of humans, setting the camera outside and remotely shooting is the only way (intend to do it again this weekend but for my resident pesky squirrel, who we have named Ethan (after the Mission Impossible Character) You'll see how it goes if I post any pics)