Nikon Nikkor Z 28-75 mm f/2.8
6. Distortion and field of view
Field of view
A full frame rectilinear 28-75 mm lens should offer you a range of angles of view changing from 75.4 to 32.2 deg. Of course some exceptions are always possible – after all, as we are going to show in a moment, the lens doesn't correct distortion in a perfect way so is not rectilinear. What's more, its real focal length might be a tad different than the one officially declared. The producers always round such values to the whole numbers so 2-3% of difference is not anything strange. The producers themselves provide a bit different data in their declaration because according to the official specifications the offered angles range from exactly 75 degrees to 32.2 deg.Fortunately, when it comes to fields of view of the tested Nikkor, we don't have to guess. We measured them precisely as it should be done, for rays of light coming from infinity. Our measurements were based on photos of starry sky; then we transformed the pixel layout (X,Y) from the photo into the equatorial coordinate system (right ascension and declination), which locates a star on a celestial sphere.
In case of the 28 mm focal length we used exactly 200 stars positioned evenly across the frame. The transformation error amounted a tad over one minute of arc. The field, measured this way, amounted to 76.1 deg with measurement error not exceeding 0.2 of a degree. There is a piece of good news – the lens provides a tad larger field than declared, with a slight reserve for distortion correction.
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In case of the 75 mm focal length the accordance with official declarations is practically perfect. The transformation based on 100 stars allowed to measure the field and it amounted to 32.3 degrees, with the measurement error of less than 0.1 of a degree.
Distortion
When you employ the smaller APS-C/DX sensor distortion won't be especially bothersome. In fact you can spot it only at the shortest focal length in a form of barrel deformations amounting to -1.73%. After passing to the 35 mm focal length it decreases to a not especially bothersome level of -0.65%. Then it changes the sign and at the 50 mm focal length you deal with negligible pincushion variant of +0.35%. At the maximum focal length it increases to +0.57%.
| Nikon Z7, APS-C, JPEG, 28 mm | |||
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| Nikon Z7, APS-C, JPEG, 35 mm | |||
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| Nikon Z7, APS-C, JPEG, 50 mm | |||
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| Nikon Z7, APS-C, JPEG, 75 mm | |||
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There are more problems on full frame but still, the tested lens deals with this aberration pretty well, taking its parameters into account. Once again most of the problems you can encounter at the 28 mm focal length, where barrel deformations amount to -3.02%. With the increase of the focal length this level decreases very swiftly and at 35 mm it amounts to -0.98%, then the aberration changes the sign and at 50 mm you already observe pincushion deformations of +0.98%. At 75 mm they increase to +1.40%.
You can compare this performance with that of the Tamron 28-75 mm f/2.8 Di III RXD, a lens with the same parameters. It fared very similarly but at 28 mm it showed a lower level of barrel distortion and at 75 mm its pincushion deformations were more pronounced.
| Nikon Z7, FF, JPEG, 28 mm | |||
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| Nikon Z7, FF, JPEG, 35 mm | |||
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| Nikon Z7, FF, JPEG, 50 mm | |||
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| Nikon Z7, FF, JPEG, 75 mm | |||
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