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Before we start pointing out the pros and cons about this lens, we have to explain several facts that we have noticed. While measuring the horizontal and parallel MTF50 values in the center and at the ends of the frame we are able to test how the resolution, chromatic aberration and astigmatism are changing according to their location in the frame.

The results we achieved for the Nikkor 18-70 mm are very interesting. As far as 18 mm is concerned, nothing different is happening, but for the 50 mm we noticed strange behaviors. Let's look at the picture, which presents chromatic aberration on the right and left edge of the frame. You can see clearly that on the left side, while stopping down the lens, the chromatic aberration is decreasing and on the right side we have the opposite situation - it is increasing!

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Another interesting effect we noticed was the visible sharpness difference between the left and right side of the frame. The MTF50 values were higher on the right side, which is shown in the picture below.

To be precise we have to add that there is a visible astigmatism for the tested lens. Taking into consideration all the aforementioned effects, it is easy to figure out the reason for all this confusion. It is possible that in our tested lens there is a small, but measurable, inclination between its focal plane and the plane, in which the detector is situated. The effect of this situation cannot spoil the picture quality in the center of the frame, but it shows up at the edges of the frame with smaller MTF50 values, changeable chromatic aberration and a visible astigmatism.

At this point we can present the pros and cons of the tested lens.

Pros:

• very good picture quality in the center of the frame
• very well controlled chromatic aberration
• small coma
• very solid and compact build
• quiet and well functioning autofocus
• reasonable price, especially when buying together with the body

Cons:

• visible vignetting, especially at the ends of the focal lengths range
• high distortion at 18 mm
• visible astigmatism

What can we write in summary? We should congratulate users who have such a great lens, while others, for example, Canon users, are still waiting for an equivalent. When we compare the Nikkor 18-70 mm with the Canon 17-85 IS, the advantage goes to the former. Both of the lenses are sturdy, sharp and have a good autofocus. They both have visible vignetting. The Canon, however, has a bigger chromatic aberration and higher distortion; it is also much larger and more expensive. To look further we can compare the Nikkor with the Sigma 17-70 mm. Here the price is similar. The vignetting and the picture resolution are similar, but the chromatic aberration looks better in the Nikkor. The big advantage of Nikon over the Sigma is a reliable autofocus, and that would be the argument that would convince me to buy the Nikkor 18-70 mm.

Sample shots:

Camera: Nikon D200 Parameters: 70 mm, f/11.0, exp. 1/400 sec, ISO 250 File: JPG, 3872x2592 pix, 6.8 MB	Camera: Nikon D200 Parameters: 70 mm, f/4.5, exp. 1/640 sec, ISO 250 File: JPG, 3872x2592 pix, 3.8 MB	Camera: Nikon D200 Parameters: 18 mm, f/8.0, exp. 1/250 sec, ISO 250 File: JPG, 3872x2592 pix, 7.0 MB
Camera: Nikon D200 Parameters: 25 mm, f/3.8, exp. 1/320 sec, ISO 250 File: JPG, 3872x2592 pix, 3.1 MB	Camera: Nikon D200 Parameters: 52 mm, f/4.5, exp. 1/80 sec, ISO 800 File: JPG, 3872x2592 pix, 5.1 MB	Camera: Nikon D200 Parameters: 31 mm, f/4.0, exp. 1/60 sec, ISO 100 File: JPG, 3504x2336 pix, 3.7 MB