Every camera lens has a Sweet Spot. ..meaning the best aperture where the camera/lens is in focus the sharpest.
That is why most good shooters will shoot in a preset APERTURE PRIOITY MODE or A on the control dial.
One should get the most out of each lens zoom range for maximum clarity and sharpness.
Most lens are not too sharp wide open. Buying a fast f2.8 glass does not mean shooting at wide open f2.8 willl be the answer
for maimum sharpness...as a general rule of thumb one should stop the lens 2 F stops ( making the aperture lens opening smaller to get the right combo of light hitting the sensor) to get a clearer sharper picture in better focus. You have to play around abit to find out which F stop will give you the best pic. Say for a F2.8 lens that sweet spot could be F4 to F5.6 and on a tele zom top end a F5.6 lens could have a sweet spot of F8 to F10. You guys should try it out sometimes with the appropriate contrast, saturation and sharpness setting will get you a much sharper pic. By the way the shutter speed would most likely follow the f stop setting.
So don't say a certain lens is no good at the AE setting which is the point and shoot mode without making the lens work hard for it's big bucks. No photo editor can make a soft pic look good at 100% crop.
Now if I have lost you..then go to Google and type in lens sweet spot for more details.
Here are a few samples shot today with a 75-300mm f4.5-f5.6 Minolta big Beercan lens at 300mm focal length...contrast and sharpness at +3 each and saturation at +1 EV was at 00
Note on Aperture Priority Mode and Iso 200, the first shot was taken at max aperture F5.6 and the pic was fair.
The other two pics were taken with the lens stopped down set two stops to F8 and the pic improved quite alot.
I hope you now get the picture.