Comment on Alva Glen by FlippinPhil
Not sure what you mean, you asking how to get good sharpness in all crop of image?
Yeah mate, front-to-back sharpness, maximum depth of field with only f/8 aperture.
For Sigma 10-20 f8 of aperture is the best option if you going to achieve the best result of sharpness. What I'm doing to get it is also distance from I'm focusing the subjects. That means I very often avoid being to close eg. to the rocks (foreground). Even if finelly looks quite close it's just illusion. So the tripod with the camera was located much further away. In addition, a good sharpening effect intensifies in CS 
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