Soft lens question

This was shot with IS on. here is the full shot scaled down

I hate to pixel peep but I always hear tack sharp. What is tack sharp? I am expecting to much?

It's a smidge soft, but not bad. You are shooting wide open on the long end, which is usually considered slightly less sharp than the wide end. It's roughly comprable to my 24-105.

I wouldn't use this one image as a final judge of the lens performance, you are shooting handheld at only 1/100. Even with IS on, your keeper rate won't be perfect.

If you aren't going to do the formal tripod test, one way around this is to shoot a large series of images then go back and look through them to find the sharpest of the bunch. If you find one where you nailed focus and it is acceptably sharp, then you know what the lens is capable of.

Another option is to flip to manual mode, knock down the ISO and knock up the shutter speed to completely kill all ambient light, then shoot with flash. That will get rid of almost all of motion blur problems and allow you to more clearly see the performance of the lens.

were you actually shooting at f/4, and what part of her did you focus on?......was it autofocus or manual?

The crop seems OOF to me - However, to really have an idea of what your lens looks like you should shoot at ISO 100, in the studio or in the shade with natural light, using a tripod and manual focus. Only then, will you see your lens performance enough to decide if it's 'soft' or not. The shot you posted is not a good test.

It's not tack sharp in the strictest sense - it looks like slight misfocus, but could also be subject movement. But it's well within the range of "sharp", and it'll improve nicely with proper sharpening. Besides, at what print sizes are you going to be making that sharpness at the pixel level actually matters?

Another point to make is that of your level of expectations. The image crop you posted responds well to sharpening, and this could easily be made into a 16x20 print. For a handheld shot, wide open, that's not bad at all.

Is the lens going to be "tack sharp" wide open? No, not if tack sharp is the sharpest things can possibly be. Pretty much every lens does better closed down a stop or two. Plus you can't expect the 24-105 to be as good as every other lens. Mine is a great lens, and I don't hesitate to use it for anything. However, I don't expect it to be better than my 85L (it's not).

This is off a tripod NO IS

Am I wrong to expect IS to make a shot almost tripod sharp? It seems most all of my shots so far are about on par with the one I posted which is just OK as far as sharpness goes.