The Tokina AT-X Pro lenses use a "Focus Clutch Mechanism" to switch between manual and auto focus. I have found this feature easier to operate than searching for a small button on the lens; which is used by some other manufacturers. To operate the focus clutch mechanism, slide the focusing ring forward (towards the end of the lens) engaging auto focus. To engage manual focus, slide the focusing ring back, and manual focus is engaged, disengaging the auto focus gears.
With the 270AF Pro lens auto focus can be engaged at any location on the distance scale; however, manual focus must be engaged at the same location on the distance scale, where auto focus was engaged. So to engage manual focus, rotate the focusing ring while applying slight pressure until the same location auto focus was engaged is located, and the ring slides back, engaging manual focus.
The 280AF Pro lens has the same focus clutch mechanism that operates similar to the 270 AF, except manual focus can be engaged at any location.
From photos taken with both lenses, in my opinion the optical quality is excellent. Both lenses use high-quality, multicoated optical glass, the 270AF Pro II lens uses high-refraction low dispersion (HDL) glass; the 280AF Pro lens uses two aspherical lens elements: one element is molded, the other is a hybrid, and one super-low dispersion (SD) element.
This use of HDL or aspherical and SD elements helps produce extremely sharp photos with great contrast, especially in the F5.6 to F16 range, and F22 is darn good too. Flaring has not been a problem with either lens, primarily due to the multicoating, I believe. Primarily, I use Fuji Velvia and Provia, Kodak E100VS, and Agfa RSX-II 200, and have had many photos enlarged via Ilfochrome process to 8 x 12 and a few to 16 x 20. The slides and photos display excellent sharpness and contrast. Since I primarily take only landscape photos, if there is any pincushion or barrel distortion I would not notice it, since Mother Nature has no straight lines.
Here is where I judge that Tokina AT-X Pro lenses excel over all other non-OEM lens manufacturers. Other manufacturers may have great optical quality; however, I have never seen any other non-OEM lens manufacturers to have build quality as excellent as Tokina AT-X Pro series lenses. Tokina AT-X Pro Series lenses are manufactured with aluminum barrels with chrome-plated brass lens mount. A black rough (crinkle) type finish is applied to the lens and rubberized coatings are applied to the focus and zoom rings. The pattern on the two rings is different, and I guess in some situations this can help a person identify the different rings by feel. However, the older you get, the more callused your fingers are, so this difference in coating patterns on the rings does nothing for me. Besides, it is easy to figure out that the ring closest to the camera body is the zoom ring, while the one towards the forward end of the lens is for focusing.
Another nice feature about Tokina AT-X Pro lenses is the focusing ring is dampened when manual focus is engaged. This allows for a "better feel" when manually rotating the focusing ring. Similar to what a true manual focus lens feels like. The zoom ring is smooth to operate and gives just enough resistance to make it operate smoothly when rotating.
I will never say either of these lenses is as good as a comparable Nikkor, since I do not have the comparable Nikkor lens to test against. One good feature of this lens over a comparable Nikkor lens is the price. The comparable Nikkor will be more than double in cost, and in my opinion, under most circumstances you or anyone else will never be able to notice a difference; especially if you are taking landscape photos.
The following specifications for the AT-X 270AF Pro II lens and 280AF Pro lens are taken from Tokina Advertising Brochures; however, I did some revisions to commonize the specifications such as the order of the specification in the list, metric first, etc., but no actual specification has been changed.
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