A couple years back I found an awesome deal on a manual focus Tokina 300mm f2.8, which I ended up purchasing. It was quite the lens with a 114mm front element protector.
I then had a brainwave. I set the lens on a tripod on inside on our dining room window and set up a bird feeder on the back deck. As the lens had a trip mount, this allowed me to leave it up and take the camera off when I was using it for something else.
The lens was hooked up to a Nikon TC-16A teleconverter which has an AF element, allowing autofocus when using manual focus lenses – very nifty. It won’t auto focus the full range of the lens, but if you get somewhat close using manual focus, the AF will look after the fine adjustment and takes out any guess work.
A 300mm f2.8 hooked up to a 1.6 teleconverter on a DX camera effectively gave 720mm at approx f4.5. Pretty nice indeed. All the photos are actual size (no cropping) and the bird feeder was approximately 5 meters from the camera.
Interestingly, with the seed we put in the bird feeder, it almost exclusively attracted cardinals, few other birds were interested. The bright red one is the male, with female being more muted browns, with a dash of red-orange.