slightly bored, more slightly curious. I wanted to see just how sharp of a picture you could get using extenders. The setup: 70-200 f/2.8 IS -> 2x Extender -> 2x Extender -> 1.4x Extender -> 40D. this works out to 1120mm f/5.6 lens (magnified 1.6x by the 40D) I aimed the camera at the yellowish tree out by the street (boring landscape outside of my house). You can faintly make it out in this picture. I'd estimate it to be about 300 feet away. This is the picture it took, straight from the camera. RAW, f/9, 1 second exposure. I used mirror lockup and focused with 10x magnification in Live View. Here is a 100% crop. pretty sharp, but entirely worthless. Good to know though.. i think?