As we have seen in the Part I, when we shoot at F8 and position the main subject in the centre, most lenses perform quite well.
In this installment, we’ll look at the left and right edges, exposed at F8.
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The first set shows 100% crops of the left edge.
1. Nikkor 18-55/3.5-5.6 – ISO 320, F8, 1/1250s
2. Nikkor 18-70/3.5-4.5 – ISO 320, F8, 1/1000s
3a. Nikkor 50mm/1.8 – ISO 320, F8, 1/1600s
3b. Nikkor 50mm/1.8 – ISO 320, F8, 1/1600s
Exposure adjusted (lightened) to match with the Sigma exposure (1/1000s)
4. Sigma 50mm/1.4 – ISO 320, F8, 1/1000s
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The second set shows 100% crops of the right edge.
1. Nikkor 18-55/3.5-5.6 – ISO 320, F8, 1/1250s
2. Nikkor 18-70/3.5-4.5 – ISO 320, F8, 1/1000s
3a. Nikkor 50mm/1.8 – ISO 320, F8, 1/1600s
3b. Nikkor 50mm/1.8 – ISO 320, F8, 1/1600s
Exposure adjusted (lightened) to match with the Sigma exposure (1/1000s)
4. Sigma 50mm/1.4 – ISO 320, F8, 1/1000s
The two zooms performed again very similarly, and show significant detail deterioration even at F8 aperture. The inexpensive 18-55mm kit lens was perhaps slightly better than the 18-70mm lens. The tested kit lens was newer than the tested 18-70mm zoom which may explain the difference in image quality.
The 50mm/1.8 Nikkor was visibly sharper than both zooms, and the contrast seems also better.
Sigma 50mm/1.4 renders the shadow details even better. Too bad, the camera metered 1/1600s for Nikon 50/1.8 lens and 1/1000s for Sigma 50/1.4, because that makes the 3a picture darker, so I tried to compensate for it by adjusting the curves and lightening the Nikon 50/1.8 shot (picture 3b).
Interestingly, Sigma lens exhibited some light pink patches on the white ship.
CONCLUSION:
The two primes demonstrate clearly their higher quality on the outside edges.
If you use the 18-55mm kit lens or the 18-70mm Nikon lens, position your main subject in the middle, and the background is not too important or in the far distance, you won’t notice any problems. However, if you are shooting a landcape scene and want it to be sharp from edge to edge, when using the above zoom lenses you’ll incurr significant penalty on the outside perimeter of the image. In that scenario, the prime lenses will do a much better job.
In the Part III, we’ll look how these lenses perform at the wider apertures.
advantica 
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