Quote: bob 00: So if the problem is caused by misalignment, does that mean there was a simply a bad time/batch of lenses produced, or is it simply luck of the draw... if most of the problems were noted 2008/2009, would tamron have rectified the problem by now? or is the rate of problematic copies so low that it is a matter of the vocal minority getting more attention in the reviews???
I have been skimming the internet for reviews, which seem to be resoundingly good for the 28-75, and it seems thaAm I wrong in that?
Bob, neither Tamron nor other lens manufacturers, are going to release failure statisitics for their lenses. You make a good point, and ask good questions, but I do not think it is possible to know, beyond a doubt, if the ff/bf issues are better in 2011 than they were in 2008. There is no solid data to back any valid conclusions. However, you could call Tamron and ask them--they have always been helpful to me, though I never sought this kind of informtation from them. If you do call, please release anything you learn, here, at the forum.
I do think we can safely assume more 28-75s, & lenses in general, focus accurately on more DSLR bodies since Micro--AF adjusment has been implemented. Of course, this says nothing about whether or not actual lenses are controlled to higher standards of bf/ff. In fact, lens makers may actually spend less time with control of ff/bf since they know micro-af adjustment is becoming the norm. Sadly, & this is not just in photography, quality control is no longer a department in a company; rather, quality control has been passed on to the buyer.
I can't agree with this statement of yours:
"the problems are heavily weighted towards the Pentax mount.... " If you look here,
FM Reviews - Tamron AF 28-75mm f2.8 XR Di Zoom you will see 175 owner reviews, with an average score of 8.6 for C & N owners of the 28-75. If you check Pentax Forums here,
Tamron Macro SP AF28-75mm F/2.8 XR Di LD Lens Reviews - Zoom Lenses - Pentax Third-Party Lens Review Database you'll see 35 reviews with an average score of 8.6 for Pentax owners of the 28-75. There is nothing statistically relevant which can be gleaned from crunching these numbers.
Anyway, all this philosophizing over the issue is better left by the wayside. If you really want a good 28-75 f 2.8 it is an easy thing to get. We are not searching for a rare coin here. You simply need buy from a dealer or seller who guarantees your satisfaction. Sure, you might get a bad copy, or 2, but you are sure to get a good copy if you pursue the issue. Important to keep in mind: 1 copy may focus fine on 1 DSLR body, but not on another body---the quality control is not just a factor in lenses.
Best of luck to you,
JT