Technical Question

I am trying to determine if my 24-70 2.8L has a focusing issue. I use it to shoot senior shots and they are all, IMO, soft. I performed the battery test but I don't think I did it right but I did not strive to have my shutter speed the reciprocal of the lens length. I will redo but I have already noticed that at 24mm it is really soft and at 70 mm it is really sharp. Is that normal? Also, is that because I did not get the shutter speed fast enough. I guess I don't understand. I should probably set my lighting up to allow for a minimum of 1/100 shutter, right? LJE

Why not post some images?

Post some examples.

Redo your tests on a tripod using miror lockup and using a cable release then post them. Make sure you focus on a flat target a more than large enough to cover the centre focus, use the centre AF point only.

Try a faster shutter speed too at 24mm if your subject is far away from you.