In the following test, I set the camera up on a tripod, used mirror lock-up, and fired with a cable release. I used AF to focus on the bark of a tree. Camera was set to ISO-100 and all shots taken at the "tele" end of the lens where I normally shoot. I shot one raw frame fully open and one frame stopped down by -1.0.
I imported the images into Photoshop with default corrections. sharpening 50%, radius 1.0, no smoothing. On the images taken with the extender, I cropped to a 2:3 region at the center of the frame with width 1400. On the images taken without the extender, I repeated the cropping with a width of 1000. I then stretched these two frames to a width of 1400. All four frames were saved in highest resolution JPG.
|Canon EF 100-400mm II - 400mm, f/5.6, ISO-100|
|Canon EF 100-400mm II - 400mm, f/8, ISO-100|
|Canon EF 100-400mm II with Extender 1.4x III - 560mm, f/8, ISO-100|
|Canon EF 100-400mm II with Extender 1.4x III - 560mm, f/11, ISO-100|