AF-S DX Zoom-Nikkor 18-70mm f/3.5-4.5G IF-ED lens review

Introduction This lens was introduced together with the Nikon D70 as its kit lens and sells separately for about USD300. It is a DX format lens which means that it is designed for digital SLR cameras with a 1.5X field of view crop and will not work on Nikon 35mm film cameras. It has no aperture ring (G-type), no constant maximum aperture (it changes from f/3.5 at the wide end to f/4.5 at the long end) and no depth-of-field scale. It, however, boasts an ample range of focal lengths (equivalent to the venerable 28-105mm range on 35mm film cameras), an inbuilt silent wave motor for faster focusing (AF-S), as well as three extra-low dispersion (ED) glass elements to produce better image quality. Visit here for links to other reviews of the lens. If necessary, you can find simple explanations of the terms below here.

Built quality and handling

The lens is very light (390g), quite small and handles perfectly on a Nikon D70s, which is not entirely unexpected as it was designed for the camera. Built quality is pretty much on par with that of the D70s, too. It is made of plastic and operation of the M-A/M button and zoom ring is rather stiff, especially if you compare it side-by-side with pro-level Nikkor zooms. Front barrel extends about an inch at 70mm; however, it does not rotate and thus will not pose any problems when using filters. Autofocus is silent and sufficiently fast.

Focusing and zoom rings are reversed in position, i.e. focusing ring is now closer to the camera. Although some photographers might find this confusing, I can comprehend why this design was adopted: this way zoom ring, which is normally used much more often than focusing ring, falls very naturally into you hand when you just grab your camera with the lens attached and do not think where what ring is. This puts focusing ring at a disadvantage - it feels too close to the camera, too thin and quite awkward in use. I personally do not think that this is a problem, though, as I generally find manual focus with 1.5X field of view crop viewfinders impractical anyway.

One minor inconvenience related to the reversed ring design is that the lens can not be used with the lens hood attached to the lens reversely for storage as in this position it covers zoom ring. This means that you have to either take the hood on and off all the time or carry it separately in your camera bag. The hood appears too shallow to provide effective protection against stray light anyway and I personally just leave it at home.

By and large, in spite of its plastic construction and somewhat stiff operation the lens does not feel cheaply made - it is built and handles more than adequately for its intended use and price.

Sharpness

Keeping in mind that this lens is intended to be used on a 6MP camera, it is very, very sharp. How sharp? I compared its performance against the venerable 17-35 zoom shooting with a Nikon D70s in RAW and then converting files to TIFF format and applying the same amount of sharpening. My results indicate that - get a load of this - on a 6MP camera and at equivalent focal length and aperture settings the lens, generally, is as sharp as the 17-35 zoom.

If one insists on being entirely neurotic, the 17-35 zoom is a tiny bit sharper at some settings (mostly wider apertures) and 100% magnification. That said, though, this extra sharpness is almost imperceptible and one has to look for it very thoroughly to actually see it. The difference is so insignificant that for all practical purposes I would consider it pretty much nonexistent when the lenses are mounted on a 6MP camera. In other words, the 17-35 zoom is sharper but it would take a camera of significantly higher resolution to accentuate the extra sharpness.

I also compared the lens' performance against the 70-200 zoom set at 70mm. I also compared the lens' performance against the 70-200 zoom set at 70mm. At 100% magnification the 70-200 zoom is visibly sharper at all aperture settings and the difference in sharpness is more pronounced than when the lens is compared against the 17-35 zoom.

Light fall-off

Even though this is a DX lens which needs to produce a smaller image circle, light fall-off is present throughout the whole range of focal lengths. It is not worse than in case of many D-series fixed focal length (prime) Nikkor lenses mounted on full-frame film cameras, though. Approximate apertures at different focal lengths at which light fall-off is gone are as follows (note that I am being quite picky here):

18mm (max aperture: f/3.5) - f/6.3
24mm (max aperture: f/3.8) - f/5.0
35mm (max aperture: f/4.2) - f/6.3
50mm (max aperture: f/4.5) - f/7.1
70mm (max aperture: f/4.5) - f/7.1

I should also note that between 24 and 50 mm light fall-off is much more gradual and thus less noticeable in real-life prints.

From a certain perspective one can say that in order to keep the lens light and small this part of its performance has been transferred to... post-processing software, which efficiently deals with the aberration. We should realize and accept that in digital photography post-processing is an inseparable part of an image and if post-processing software can effectively remove any remainders of an aberration than it can be neglected for practical purposes.

Distortion

As far as distortion is concerned this lens performs much, much better than one would expect from a USD300 zoom - in fact, this level of performance would be perfectly acceptable for a lens of a significantly higher cost. The test photos below are full-length images.

Distortion at 18mm

At the wide end distortion is a sort of a mixed bag. On the one hand, its signature is quite complex and in the shape of a stretched "w". On the other hand, it would have been more pronounced and noticeable had it been of a simple barrel kind. For most photographers who do not look for the aberration in their images on purpose this, of course, is excellent. For the most demanding photographers this might be a bit problematic, though, as the sophisticated distortion signature might prove difficult to effectively correct during post-processing. But then again, the most demanding photographers do not use lenses of this class.

Distortion at 24mm

Distortion at 35mm

Distortion at 50mm

Distortion at 70mm

From about 24mm the lens starts showing an almost indistinguishable pincushion distortion which remains very mild throughout the rest of the focal length range.

Other performance factors

In spite of the fact that I never use the lens hood I am yet to encounter any problems with flare and ghosting. Chromatic aberration is well controlled, too. Bokeh should not be a major concern with the lens considering its focal length range and relatively low speed.

Conclusions

This is the ideal lens for a 6MP camera (read Nikon D40, D50 or D70s); at USD300 it most certainly represents a superb value for the money. On my D70s I actually prefer it to the 17-35 zoom for its extended range of focal lengths, significantly lighter weight, smaller size and comparable image quality. As with any lens, learn how it behaves at different focal length and aperture settings to get the best image quality possible.