Tamron 18-400 mm f/3.5-6.3 Di II VC HLD
5. Chromatic and spherical aberration
Chromatic aberration
The Tamron 18–400 mm f/3.5–6.3 Di II VC HLD doesn’t have any serious problems with the longitudinal chromatic aberration even though you can notice slight colouring of out-of-focus images. What’s interesting, the intensity of that colouring seems to increase very slightly on stopping down the aperture and is a tad lower at the maximum relative aperture. |
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You see at once there are a lot of problems. The weakest performance can be noticed at the maximum focal length, in an area close to the maximum relative aperture where the aberration level reaches a high value of over 0.2%. Significant results can be also observed at 50 mm. The 18 and 100 mm focal lengths are borderlines between a medium and high level; only the 200 mm focal length allows you to get rid of chromatic aberration problems.
The Tamron performance compares unfavourably with that of the rivals. The Sigma 18-300 mm never exceeded a level of 0.13% and the Nikkor 18-300 mm had weak results only at longer focal lengths and near the maximum relative aperture.
| Nikon D7000, RAW, 200 mm, f/8.0 | Nikon D7000, RAW, 400 mm, f/6.3 |
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Spherical aberration
It would be difficult to notice any “focus shift” effect in first photos of this chapter. Still the photos of out-of-focus circles do feature some differences. Images before the focus have a darker centre and a noticeable rim; after the focus you get a lighter central area and a bit less pronounced rim. These aren’t big effects so it seems the Tamron 18-400 mm doesn’t have any serious problems with spherical aberration.
| Nikon D7000, 200 mm, f/6.0, in front of | Nikon D7000, 200 mm, f/6.0, behind |
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| Nikon D7000, 400 mm, f/6.3, in front of | Nikon D7000, 400 mm, f/6.3, behind |
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