|Going Wildly Wide: AFS 12-24 mm f/4 G ED IF DX Nikkor Reviewed|
|by Bjørn Rørslett|
3. Optical Performance
Sharpness is traditionally one of the more important criteria for photographic lenses. We all want our lenses to be tack sharp, period end period. Yet sharpness by itself cannot guarantee anything, and I repeat any thing, in terms of the ensuing pictorial outcome. The world is flooded with sharp, dull, and uninspiring images, simply because the photographer believed his job only was to press the button and let the camera and lens do the rest. This is a paradox the handling of which each and every one of us has to balance in our own chosen manner.
I for one strive for visual impression - not visual accuracy - in my photography, so spend considerable time on assigment to circumvent restrictions imparted by a dull photographic life-likeness. I do care about lens sharpness by all means, but not as the panacea to solve all photographic problems. Commitment to the process of creating images will outperform any MTF plot any time. It's nice to have a sharp lens but better still to know to which ends it can best be used. Oh well, I continue to evaluate visual quality by shooting test pictures of brick walls outside my office, I always have and probably always shall do assessments this way. At least this procedure provides me with a guideline as to how the lens performs. I always cross reference my observations with original slides (or files) from similar lenses so to have a concistency on my rankings.
I made a number of my traditional brick-wall test shots with the AFS 12-24 DX, and augmented later on with a new test series aiming to show how the lens performed at closer range.
Subjective Evaluation of the AFS 12-24 mm f/4 DX Nikkor
(for test setup, and criteria, see here. Remember these values give qualitative - not quantitative - data, and thus averaging the values is meaningless)
|Performance at 12 mm|
Performance at 18 mm
|Performance at 24 mm|
|All tests obtained with Nikon D1X using NEF raw files processed in Bibble 3.1a. Lens mounted on a Sachtler ENG 2 CF carbon tripod with Burzynski head.|
Overall the AFS 12-24 DX lens delivers very good to excellent image quality across its entire focal range. As I found with other recent Nikkor zoom lenses, the 12-24 DX performs better at its long end. In fact, the performance at 24 mm is exemplary and is of a high professional class. I wouldn't hesitate to put the zoom control towards shorter focal lengths either.
Image contrast showed just a trace of internal flare at f/4 and improved at f/5.6-f/11. A slight softening of contrast occurred from f/16 and was quite visible at f/22. The decline in performance at smaller f-numbers is inherent in all lenses and is caused by diffraction. If anything, image quality of the 12-24 holds up much better than expected when the lens was stopped well down.
Geometric distortion is of the barrel type at 24 mm and is visible there, but not occurring to a detrimentral degree. As you zoom the lens to wider focal lengths, distortion is reduced and around 18-20 mm you have a lens suitable even for architecture work. Towards shorter settings, the geometric distortion, predictably, picks up and a barrel-type of distortion is plainy visible at 12 mm. There must be higher-order components in the geometrical rendition too, because the lines curve much more towards the extreme corners. You should not consider shooting architecture with this lens set at 12 mm.
Curvature of field was negligible at the long end of the zooming range and thus images were sharp corner to corner even at f/4. At 12 mm however, curvature might be a bigger problem and was readily apparent to give quite soft corners unless the aperture was moved beyond f/5.6. I expect the typical usage for a wide-angle zoom lens is for shooting at quite close range, rather than the infinity-focus type of tests I run initially. So, in a new test series, shots were made at a distance of 1 m, and although the field curvature still persisted for the wide (12 mm) setting, the curvature wasn't further aggravated. Although the lens clearly not is a flat-field "macro" design, you can get nice close-ups with it by keeping the aperture to f/8 or smaller and restrict zooming to the long end of the range.
The chromatic issue is addressed on the subsequent page, so get the salient details there. For now, suffices to say that Nikon has succeeded in keeping colour fringing at bay for a great deal of the focal range encompassed by the lens. Not unexpectedly, issues remain at the very widest settings. Seen as a whole, the lens design is first class indeed, taking into account the very wide angles of view covered by this zoom lens. The commendable lack of vignetting adds to the pleasing impression, too.
The DX concept is intimately linked with the current small-sized digital sensor of Nikon D1-series and D100 cameras. Of course, DX lenses apply to the Fuji S1 and S2 cameras as well. However, the 12-24 DX can be mounted on any camera with an "F" bayonet, and indeed will illuminate the entire frame of 24 x 36 mm of my F5 when the focusing control is set between 16 and 24 mm. Any wider than this with a full-frame camera and you'll get dark corners, very large and dark by 12 mm in fact. Normally the image circle of any lens increases when the lens is focused closer, so I thought initially that I could manage close-ups at 12 mm with the DX lens attached to my F5. I was proven wrong, however, because the expected behaviour simply doesn't manifest itself with this lens, on the contrary, the image circle stays the same or even slightly decreases towards the near-focus limit. I suspect this results because the light rays from the exit pupil of the DX lens are strongly collimated to exit nearly in parallell. Another indication that the optical design of the 12-24 DX is highly sophisticated, and a likely explanation as to why the DX gets away with so little light loss towards the image corners, even at the huge angle of view at 12 mm.