General acceptable focus performance?

There have been LOTS of posts about focus tests, "soft lens copies" etc.

I wonder if there are general guidelines about acceptable focus performance. Let me give some specific questions so you see where I'm going with this.

My Sigma 24-70 @ 24mm (widest end) seems to front focus. In a "battery test", it seems to focus a little less than 1 inch in front of the focus point at 3 feet distance and the widest apperture (2.8). My Sigma 30mm performs roughly the same. Is this within reason? How much front focussing is accpetable? When does it get unacceptable?

On the other end (@70mm), my Sigma 24-70 seems to be perfect (focus-wise).

Performance @ "normal" use with the 24-70 is so far satisfying.

Are there general guidelines as to what to expect at different focal lengths (wide open)? Is for example one inch FF at 3 feet within bounds?

And is there an established "trade-off" for zooms? That is, if we tweak one end, will the other end suffer?

Any "rules" out there?

Thanks,

"softness" has to do generally with the quality of the sharpness the lens gives when in focus.

front-focusing/back-focusing is another issue. i personally never muck around with so-called controlled tests. theres too much margin for user error and in the end if it performs well for what you actually need it to do, who cares about batteries. now if your lens doesnt perform in real world situations to what you would like, then its time to get it calibrated, or look for a new lens.

On a non-pro body Canon's spec is "within depth of field", differnt ways it can be worked out but at 3ft 24mm f2.8 DOF must be around +/-8mm or about an 1/3 inch.

Considering the number of varables in the battery test method that sound OK to me.