Lens distortion / softness question

I imagine this is a dumb question. It's the first time I've ever tried to objectively test out a lens though, so I'm not positive what I'm seeing here, and was hoping someone could tell me.

The following three shots were taken with a 28-135 f/3.5-5.6 IS USM lens, at 135mm, with the box only about 12 inches from the lens... in other words, the lens was focused almost at its macro stop. They were taken at f/5.6, f/8, and f/16, respectively. Focus point was the big "6" in the center:

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Stearmandriver,
If the lens is great in normal settings then just use it! The photos you posted of a flat subject at close distance is not what the lens is made for. It is also common for lenses to get sharper when they are stopped down as it showed in your photos (f/8 - f/11 is know as the sweet spot). Now go out and use the lens

Stearmandriver,

just some thoughts ...

... it looks that you had the camera at an angle to the subject. This might explain why the pictures @ f/8 and f/16 are better than @ f/5.6 (larger DOF covers out-of-focus areas)
... at f/5.6, the lens is wide open. Plus, the 28-135 is not a lens especially noted for its sharpness. So it's not a big surprise for me that the f/5.6 image is not that sharp. The image @ f/8.0, OTOH, looks great to me.

Best regards,
Andy

Thanks guys, that's what I thought. Just wanted to make sure I wasn't too ignorant to spot an actual problem while the lens would still be easy to replace. I'm pretty happy with it stopped down though, so it's all good!