Longitudinal Chromatic Aberration and focus shift
With lenses offering an aperture of f2.8 or larger I test for longitudinal CA (loCA, a.k.a. “axial color” or “bokeh CA”). The new Tamron shows only little magenta coloration in the foreground (left) and greenish hues in the background (right). By f5.6 the effect is gone. This is very good. The test also revealed very little focus shift.
Still, axial colors can show up in real-life shots as the following 100% crop reveals:
But it’s not as strong as in Tamron’s 45/1.8 VC or the 35/1.8 VC.
Sharpness and contrast
Let’s have a look at the theoretical performance of the new lens first compared to the Nikon 85mm f1.8G ED:
These charts show the lens-performance at the largest aperture. Higher values are better and the closer the dotted and the continuous lines of each color are together the less astigmatism (= resolution depends on the orientation of the test-pattern) the lens has. The x-axis displays the distance from the optical axis (=center of the sensor) in mm. I’ll show you the real-life performance at 4 mm (center), 13 mm (DX-corner), and 20 mm (FX-corner) on a D810.
From the charts, the new Tamron should perform better than the Nikon. Especially at 30 line-pairs/mm the Tamron (gray lines) shows a much higher contrast than the Nikons (petrol lines). But let’s see how this theoretical performance translates into real life results in the sharpness test based on Siemens-stars.
What follows are near-center results (first column) followed by APS-C/DX-corner results and FF/FX-corner results on a D810. Processing was done in Lightroom 6.4 from RAW at Camera Standard settings. Noise-reduction is set to 0, sharpening to 35/0.5/36/10, with no extra tone, color, or saturation-adjustment. White-balance was adjusted to a neutral white and I did some exposure compensation to make the brightness match. CA-removal is ON.
The following are all 100% crops!
These 100% crops directly from a 36MP D810 sensor show that this lens delivers a very good performance across a full-frame sensor right from the start. The FF/FX-corner is especially noteworthy with almost no coma to be seen. It looks even just a little better than the APS-C/DX-corner which needs stopping down to f2.8 to become excellent. There was almost no need to optimize focus for the different crops: proof that the lens has no field-curvature to speak of. With such a sharp lens you can see diffraction start taking off the “bite” of the lens already at f8.0 if you look carefully.
Following is the performance of the Tamron 85/1.8 VC (1st row) directly compared to the Zeiss 85/1.4 Otus (2nd row), Sigma 85/1.4 EX DG (3rd row) and the Nikon 85/1.8G (last row) at f2.0. Please note that the Zeiss, Sigma and Nikon were shot on a D800 which has a slightly softening AA-filter. I tried to compensate for this as I used a stronger sharpening of 70/0.5/36/10 on those shots:
This comparison is proof that the Tamron is indeed an excellent performer. Compared to the mighty Zeiss Otus the Tamron can keep up in center sharpness, is only a little behind at the APS-C/DX-corner, and performs even a tad better in the FF/FX-corner. The Sigma 85/1.4 EX DG only claims fourth place in this comparison suffering from lower overall contrast and strong spherical aberrations. It clearly shows its age here and Sigma should urgently be updating this design to match the performance of their “Art” series. The Nikon shows again that it’s a pretty good performer especially considering its low price.
Performance at long distances
The Siemens-star test-targets are shot at a distance of 40x focal length (i.e. at 1.8m for 85mm focal length). But performance of lenses also depends on the shooting distance. Therefore I present another series of test-shots of a landscape dubbed the “Unremarkables” where you can measure distances in km, not meter. Processing was done in Lightroom 6.4 from RAW at Adobe Standard settings. Noise-reduction is set to 0, sharpening to 35/0.5/36/10, with no extra tone, or saturation-adjustment. There’s no tinkering with vignette-control so you see it here as it is produced by the lens. Focus was acquired at the largest aperture manually and not changed for other apertures.
You can click on each image to access the large original. Please respect our copyright and only use those images for personal use.
The main image shows the complete scene at f1.8 to give you an impression of the angle of view and to judge vignetting. This is followed by one row of 100% crops at different apertures each from near the middle, the DX/APS-C-corner, and the FX/FF-corner. You can access the respective shots up to f16 via the links beneath the main image.
Following is a comparison with the Zeiss 85/1.4 Otus shot only a few minutes later at f1.8:
Performance of the Tamron wide open in this long-distance shots looks again very impressive up into the FF/FX-corner which profits from the very low coma of this lens. Compared to the Zeiss Otus the Tamron looks a bit less sharp in the center, equal in the APS-C/DX-corner and sharper in the FF/FX-corner. So optically the new Tamron is a very good performer near and far even surpassing the Otus in the corners of a full-frame sensor – which is quite a remarkable result!
To make it easier to compare light fall-off in the corners of a full-frame sensor I’ve arranged a series of three shots each with the Tamron (1st row) and the Zeiss Otus (2nd row) at different apertures. From left to right: f1.8, f2.0, and f2.8:
As you can see, the differences under controlled conditions favor the Zeiss 85/1.4 Otus. But that was to be expected as it is already stopped down by 2/3 at f1.8.
Rendering of point-light sources at night-shots
Night-shots pose a different challenge for lenses as the contrast is even higher than under bright sun and point-light sources can reveal some weaknesses such as coma, haloing and color-aberrations that do not show up as prominently in other test-shots. The 100% crops below the main image show the effect of coma in the FF/FX corner of this lens at various apertures:
As demonstrated in the other tests above the lens has indeed a very good correction for coma. This is responsible for the excellent resolution in the FF/FX-corner.
Rendering of out-of-focus point-light sources
This test is for the rendering of point-light sources in an out-of-focus background. The circle of confusion that is produced by this test is pretty indicative of Bokeh performance (in the background) and light fall-off. Ideally the out-of-focus image of the point-light is evenly lit and perfectly circular, with no “onion-rings”, and without coloration. Large aperture lenses normally produce an effect known as “cat’s eye” the further away from the optical axis the point-light is projected. This is due to optical vignetting in the lens barrel when light enters the lens from an angle.
As the 50% crops above show: The Tamron 85/1.8 VC produces quite a nice circle of confusion. It exhibits no onion rings as befits a lens without aspheric elements. There’s only a weak, slightly green outline indicating the low longitudinal CA of this lens, and light-distribution across the circle outside the optical axis is pretty even. But there’s a clear cat’s-eye effect towards the borders/corners of the sensor and some clipping from the mirror-box.
Following is the same shot done at f1.4 with the Zeiss 85mm f1.4 Otus for comparison:
As you can see the 85mm f/1.4 lens produces a 20% larger circle of confusion near the center which stems from the larger aperture. The “Bokeh balls” of the Otus show some weak onion rings but even less of an outline than from the Tamron.
Now let’s see how this analysis of out-of-focus point-light sources translates into Bokeh-performance shooting a book-shelf.
Following is the same shot done with the Zeiss 85mm f1.4 Otus for comparison at f1.4:
While the Bokeh of the Tamron at f1.8 is actually quite nice and only a little nervous it cannot match the Otus at f1.4. But that’s what you get an f1.4 lens for, isn’t it? Using both lenses at f1.8 reduces the differences considerably although the Otus stays a bit creamier in the foreground and background but still shows a slightly stronger coloration in the middle-ground.
Catching a strong light-source shining directly into the lens is always a risky business. It could produce strange colorful ghosts-images or reduce contrast considerably through flare and glare. The appearance of flare and ghosting depends on factors like the aperture and the angle of the light hitting the lens. So to judge the proclivity of the Tamron for these artifacts I went through a series of well calculated shots against a strong light source to provoke glare and ghosting. The lens hood was attached in all of these tests.
The results are so-so. With the light inside or just at the corner of the image-frame the artifacts are pretty strong – although to be fair: the test-conditions are quite extreme. But when the light was clearly outside the frame (but still shining into the lens) there was only little flare, streaking or ghosting. Following are two of the more extreme effects: