Try a faster shutter speed you might be having handheld problems


Try the lens at 5.6


It is tough for a lens to start at infinity


The depth of field of the for that lens at 3 feet f1.8 is


near limit 2.97


far limit 3.07


for a total depth of field of .07ft (.03 ft is in front of the subject and .04 ft is behind the subject)


you might be asking too much at this close distance


try it at a longer distance


(or you might try a 10foot laptop, works for me)