Digital Dave's Ruminations

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...where Digital Dave occasionally shares his thoughts on China, Photography, and other various and random subject-matter.

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Friday, February 13, 2009

Nikon's new AF-S Nikkor 50mm f/1.4G vs. AF-Nikkor f/1.4 D


       Nikkor 50mm f/1.4  AF-S                Nikkor 50mm f/1.4  AF-D

I've had the new AF-S Nikkor 50mm f/1.4G since it was released last December and I've been using it consistently on my D700 and D3.  In fact, it's been the most commonly mounted lens on my full-frame cameras this winter because I've mostly been photographing Oliver, whom I don't usually have until his mom goes to work at 6:00 PM when it's already dark. So I'm primarily shooting indoors in dimly-lit rooms and occasionally outdoors under street lighting.

Of course, the high-ISO capabilities of the D3/700 combined with the wide, f/1.4 maximum aperture of the 50mm, make it possible to routinely shoot in those conditions without the use of flash (a real paradigm shift for most photographers) but it generally necessitates that the lens be shot wide-open at f/1.4, which is not typically the sweet-spot at which a lens attains its maximum performance. So while most of my shooting with this lens has been  under less-than-optimal conditions, it's been useful to see what the lens can do wide-open. After all, we buy a super-fast lens to actually use it at its maximum aperture.

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50mm f/1.4 AF-S @ f/2.0. Not the world's prettiest bokeh, but an improvement over the AF-D.

Physically, the new lens is somewhat bulkier than the AF-D, though not perceptibly heavier. It takes a 58mm filter instead of the 52mm that was standard on Nikon's 50mm lenses for decades. Also changed from the AF-D, the front element of the new lens does not extend forward past the front edge of the lens body when focusing. And like all of Nikon's newer AF-S lenses with a "G" designation, the new 50mm does not have an aperture ring.

In terms of optical performance vs. the older AF-D version, there's no question that the new AF-S  model is a step up in quality. It is noticeably sharper at wider apertures, particularly at f/1.4, than the older lens and it has a more pleasing bokeh (background blur) as well. This is most likely due to the newer lens's nine rounded aperture blades (as opposed to the AF-D's seven non-rounded blades). Vignetting seems to be very well controlled, even at wide apertures, and corner-to-corner sharpness is quite reasonable, especially when stopped-down.

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50mm f/1.4 AF-S @ f/5.6.

Chromatic aberration is also very well controlled, with one major caveat. While the new lens does a very good job with lateral CA (which, when present, is very easily fixed in most advanced photo-editing software), it introduces a quirk not found on the older AF-D lens: longitudinal chromatic aberration. In certain situations, mostly involving very high-contrast specular highlights, color fringing that almost completely encircles the highlight can occur and, unfortunately, it is difficult, if not impossible, to fix in software. On the bright side, it seems thus far to be a fairly rare phenomenon (I've encountered it in less than ten images out of literally thousands I've taken with this lens).

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50mm f/1.4 AF-S wide-open @ f/1.4. Excellent sharpness for such a wide aperture.

Another unpleasant surprise is the presence of slight, but nevertheless visible, barrel-distortion, something not really expected on a 50mm lens. This is, of course, very easily remedied in software, but it's a shame it even has to be an issue. There was certainly no detectable amount of barrel-distortion on the older AF-D lens.

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50mm f/1.4 AF-S @ f/8.0. Stopped-down, this lens is tack-sharp.

Other than the optical performance characteristics discussed above, the primary difference between the AF-S and AF-D lenses (and presumably the reason that you'd upgrade from the AF-D to the AF-S) is, of course, the auto-focus functionality. The new AF-S uses Nikon's latest, super-fast, built-into-the-lens, silent-wave motor technology to acquire and track focus, whereas the older AF-D is screw-driven by the camera body. The expectation in this regard is a much faster-focusing lens than the AF-D. The reality is somewhat more complex than that.

If you're expecting the type of almost instantaneous, snap-to-focus performance that you are used to with most of Nikon's AF-S lenses, you will likely be disappointed, at least at first. The Screw-driven AF-D is actually faster at acquiring focus than the AF-S, and by a fairly noticeable degree. However, once focus has been acquired, the AF-S truly shines. It tracks focus far more quickly and accurately than the AF-D, especially when the subject is moving in quick, jerky motions (think kids and pets). In this regard, the new lens leaves the older one in the dust.

It's just when the AF-S has to move its focus-elements a significant distance in order to acquire initial focus that it is very noticeably sluggish as compared with the AF-D. When shooting in continuous focus mode, I've gotten in the habit of waiting an extra fraction of a second before firing-off my first shot, and that has largely remedied the problem.

(I've tested the new AF-S on both the D3 and the D700, as well as the D300, and have found it's auto-focus characteristics to be the same on all three cameras. So I'm confident that this aspect of the auto-focus performance is a function of the lens, not a particular camera body.)

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50mm f/1.4 AF-S @ f/2.0.

Bottom line? If you already have the older AF-D, the new lens is a worthwhile upgrade, even in spite of its substantially higher price, provided you are aware of, and adjust for, its particular quirks. If you have never owned one of Nikon's fast 50mm lenses, this is a great, lightweight, walkaround lens that opens up low-light environments to your photography. And if you are the owner of one of the Nikon camera bodies that only accept AF-S lenses (D40, D60), you can now have a fast, normal-focal-length, prime lens that actually auto-focuses on your camera!