The mechanical performance of a lens is just as important as the optical performance. If the lens feels bad in the hand, or loose & rickety, it will not inspire confidence. If the focus is slack or too slow, shots will be out of focus, or missed altogether. Here, the Tamron 180mm macro is both exceptionally good, and also about average.
Tamron SP AF 180mm F/3.5 XR Di LD [IF] Macro 1:1 Lens on a Nikon D100
The manual focus on this lens is a delight! It is beautifully smooth and well damped, and the very large focus ring makes handling a pleasure. The focusing ring has a sliding clutch to enable almost instant change from manual to autofocus, just by sliding the ring up or down the lens barrel by a couple of millimeters. There is a firm click stop on the clutch so you won't find yourself accidentally changing modes.
I've had some discussions about the autofocus with the dealer who lent me the review sample, and he obtained a response, direct from Tamron. Tamron comments were basically that researched the product requirements with professional photographers prior to design. The feedback they had from serious photographers was that AF is rarely used in very close-up photography as time is generally spent focusing manually quite exactly, considering depth of field requirements, hyperfocal distance, etc. They therefore concentrated on optical and build quality and were able to produce an excellent lens at an affordable price. Tamron just received a 4 star rating from German Photo magazine for this product.
This is a specialized lens and not really designed for general purpose fast point and shoot work, fast AF is not important for this type of user. There are many other Tamron lenses designed for this other purpose.
The focus throw on this lens is very long, 270 degrees from 1:1 to infinity. The majority of this is within the close-up range, allowing very precise focusing close-up. A further effect is that the autofocus is extremely accurate and locks on well, provided the light is adequate. I would like to see a focus range limit switch on the lens, so that if it fails to lock AF focus and starts hunting, the wait is minimized.