AF–S DX Zoom–Nikkor 18–70mm f/3.5–4.5G IF–ED lens review
This lens was introduced together with the Nikon D70 camera 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 or FX 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 cameras), inbuilt silent wave motor for faster focusing (AF–S), as well as three extra–low dispersion (ED) glass elements to produce better image quality.
Build quality and handling
The lens is very light (390g), quite small and handles perfectly on the Nikon D70s, which is not entirely unexpected as it was designed to be used with the camera. Build 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 ring are reversed in position, i.e. focusing ring is positioned closer to the camera. Although some photographers might find this confusing, I can comprehend why this design was adopted: this way the zoom ring, which is normally used more often than the focusing ring, falls very naturally into you hand when you handle the camera without thinking 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 focusing 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 it covers the 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.
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 with the venerable 17–35mm f/2.8 zoom on the Nikon D70s and the results indicate that—get a load of this—at equivalent focal length and aperture settings the lens, for the most part, is as sharp as the 17–35 zoom.
If one insists on being picky, the 17–35 zoom is a bit sharper at larger apertures and 100% magnification, which is not unexpected as it is a faster optic. This being said, this extra sharpness is almost imperceptible and one has to look very closely to actually see it. The difference is so insignificant that to all intents and 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 a higher resolution to accentuate the extra sharpness.
I also compared the lens' performance with the 70–200mm f/2.8 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 with the 17–35 zoom.
Even though this is a DX lens that, as such, needs to produce a smaller image circle, light fall–off is present throughout the entire 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 cameras, though. Light fall–off is virtually gone at the following apertures (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 24mm and 50mm 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 aspect of its performance has been transferred to... post–processing software, which efficiently deals with the aberration. We should realise and accept that with the advent of digital photography post–processing is an inseparable part of an image and if post–processing software can effectively remove any remainders of an aberration then the aberration can be neglected for practical purposes.
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 mixed bag. On the one hand, its signature is quite complex as it has the shape of a stretched "w". On the other hand, it would have been more 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, however, this might be a bit problematic as the complex distortion signature might prove difficult to completely remove in 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 almost indistinguishable pincushion distortion that remains very mild throughout the rest of the range of focal lengths.
Other performance factors
In spite of the fact that I never use the lens hood I am yet to encounter any problems with flare. Chromatic aberrations are very well controlled, too. Bokeh should not be a major concern with the lens considering its range of focal lengths and relatively low speed.
This is the ideal lens for a 6MP digital camera (e.g., Nikon D40, D50 or D70s); at USD300 it most certainly represents a great 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 overall comparable image quality. As with any lens, learn how it performs at different focal length and aperture settings to get the best image quality possible.