Made a trip to the Texas Gulf Coast immediately following a strong spring cool front. Numerous warblers slowed by the strong north wind made for a great day! The biggest problem taking pictures of small warblers, not to mention that they are very tiny and often do not want to sit still, is the very small depth of field, which is often only a fraction of an inch when taken near minimum focusing distance with a 600mm lense. It you can get the beak and head in focus in a closeup anything beyond that is a bonus.