The automatic setting always comes in with a F4.0 or so focal length (is that the right term?).
No, f4.0 is the aperture. You should be shooting at f10 and up, but not over f16, unless
you're trying to get a sun star.
The more open your aperture the more your reducing what will be in focus, useful
for wildflower or macro photography, but not for landscape photography, unless your
particular lens is the sharpest at f4.0, and then one would use focus stacking, which is
a technique/software used by photographers.
Shoot manual, take a reading of the clouds to the right or left of where the sun is
setting, lock that setting, recompose, and shoot, if you have it on auto, your camera
will automatically adjust for the sun, which is not what you want.