Rack 'em and stack 'em! This was a test of stacking two Canon Tele extenders (a 2.0 and a 1.4) onto a Canon 100-400mm zoom telephoto L lens. From experience this hasn't given stellar results with still photography, even with the latest Canon 5D Mark 2 nor 7D models with respect to sharpness. However, 1080p video is another ballgame altogether, and the outcome of this trial is actually quite impressive.
Distance to the birdbath was measured at 66 feet, slightly more to the pine treetop where the Song Sparrow is chirping. The "Uninvited Guest" was spotted at the foot of my backyard, approx 130 feet away.
Editing was done with Adobe Premiere Pro CS5.
A more thorough description of this trial is outlined in my blog: rilstone-naturephoto.blogspot.com/