Originally posted by wlachan The internal movement came from the rear (3rd) lens group. The impact won't be as critical as the 1st group and there are many AF lenses with wobbly inner groups (not just Pentax). The one I have is firm but I also came across some really loose ones. Ideally the whole lens should be firm but if I was forced to compromise, I would rather have a wobbly rear group instead of the front. You can also tell how wobbly the rear group is by pushing it with your finger or lenspen with it pointing down. The shop owner might think you are nut though. However, so long as it doesn't sound loose when shaking slightly, I would be happy (but I reckon this is rather subjective and takes experience). I would not shake the lens violently myself for this test.
So the take-away is, from manufacturing variations/defects with the most impact on IQ to the least impact, factory misalignment >>> wobbliness in lens hood (1st group) > wobbliness in internal lens barrel (3rd group)
Let me know if that's correct.