Tamron 17-50mm Di II VC, part IV

I wrote how this lens is sharp and pretty good for its price.  Now, I know why professionals rely on the Nikkor 17-55mm f/2.8 instead.  I took this lens out for the wedding last night and was I disappointed.  Some shots were sharp but most where blurry because it could not focus properly in darker conditions.  It was not like it could not focus.  The camera sensed that the focus was on and allowed me to trigger the shutter.  The lens seemed to have mis-focused and was also hunting quite a bit before it locked on something.  I missed a number of shots and unfortunately those opportunities are forever gone.  As soon as I put the Nikkor 18-200mm lens back on, I was shooting like a pro--no missed shot, focus was spot on.  I only wished the Tamron was able to seek focus as accurately and as fast as the Nikkor but I would only be dreaming.  I think this Tamron is on its way out.  It looks like I will have to spend the extra dollars to get the quality and speed I want.