Longitudinal Chromatic Aberration and focus shift
With lenses offering a focal ratio of f2.8 or larger I test for longitudinal CA (loCA, a.k.a. “axial color” or “bokeh CA”). The new Tamron shows almost no coloration at f2.8 in the foreground (left) and in the background (right). But the lens produces some focus shift between f4.0 and f5.6: the foreground becomes less sharp when stopped down
The Sigma shows a little yellow cast in the background (right) at f4.0 but develops no focus shift:
Sharpness and contrast
Let’s have a look at the theoretical performance of the new Tamron first and compare it to the performance of the Sigma 24-70mm f2.8 OS Art:
These charts show the lens-performance of both lenses at f2.8 without influence of diffraction. To read these charts you need to know that higher values are better and the closer the line-pairs 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 (APS-C/DX-corner), and 20 mm (FF/FX-corner) on a 46MP Nikon D850 body.
From the charts, overall contrast (golden lines for the new Tamron, red lines for the Sigma) of both lenses should be quite similar and indeed very high in the APS-C/DX image circle. The grey/green 30 lp/mm line(s) also indicates a very good resolution of fine details of both lenses within the APS-C image-circle. But resolution drops pretty low in the FF-corner. Astigmatism seems to be moderate. 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 46MP D850. All shots were made at ISO 64 and image stabilization switched off. Processing was done in Lightroom 6.12 from RAW at Camera Standard settings. Noise-reduction is set to 0, sharpening to 50/0.5/36/10, with no extra tone, color, or saturation adjustment. In my comparative shots below the Sigma 24-70mm f2.8 OS Art and the Nikon 24-70mm f2.8E VR were shot on a 36MP D810 with sharpening set to 35/0.5/36/10.
White-balance was adjusted to a neutral white and I did some exposure compensation to make the brightness of all crops match. So you will not see light fall-off in the corners. Removal of lateral color aberrations is ON, longitudinal CA are not corrected.
The following are all 100% crops!
First up is an overview of the wide-open performance at different focal lengths. You can jump to the detailed results at different apertures and comparisons with other lenses by clicking on the crops of the respective focal length. Except for 29mm because the results were not so much different from 24mm or 35mm.
Tamron’s new lens is very sharp in the center throughout the zoom-range with 70mm a little softer than the rest. The APS-C-corner is also very good at the short end but softens at 50mm and 70mm focal length. And the FX-corner is mushy wide open at the short end and only a little better towards the longer end. There are also signs of a mustache-like barrel distortion at 24mm which evens out at 35mm and turns into a mild pincushion distortion towards 70mm. There are more examples to judge distortions at the end of the samples page.
If you want to see all the details and comparisons with the competition from Sigma and Nikon, read on. Or fast-forward to the performance at long distances.
Performance at 24mm:
Stopping down to f4.0 improves the DX-corner to excellent and the FX-corner becomes very good at f5.6. There is only a little field curvature.
Following is a comparison with the Sigma 24-70mm f2.8 OS Art, the Nikon 24-70mm f2.8E VR and the Tamron SP 24-70mm f2.8 VC (1st generation). The Sigma was shot on a D810 with an older, less contrasty print of the test-target and a little less sharpening of 35/0.5/36/10:
The Tamron performs clearly better at 24mm than the Sigma and is on a similar level as the Nikon. Both the Tamrons produce identical results as was to be expected from the identical optical formula.
Performance at 35mm:
At 35mm the FX-corner again profits clearly from stopping down to f5.6 although it does not come up to the same level of sharpness as at 24mm. Following is a comparison with the competition:
At 35mm focal length both Tamrons beat the Sigma and the Nikon in the DX image-circle while the FX-corner is won by the Nikon.
Performance at 50mm:
Stopping down to f4 visibly lifts the performance of the lens at 50mm focal length even in the center. Again the FX-corner needs stopping down to f5.6 to look good. Let’s see how the Tamron fares against the competition:
Performance at 70mm:
At 70mm the new Tamron profits greatly from stopping down to f4.0 as the performance at f2.8 is marred by spherical aberrations which make the light bleed into darker areas. As I found out in other test shots this can already be suppressed quite well by stopping down to f3.2 as you can see in the following 100% crops from a night-shot:
Following is a comparison with the Sigma 24-70mm f2.8 OS Art, the Nikon 24-70mm f2.8E VR and the Tamron SP 24-70mm f2.8 VC:
Comparing both the old and the new Tamron this is the first time to see some differences between both lenses: The old (A007) lens shows little spherical aberration in the center although it seems less sharp than the new G2 version. Outside the center both Tamrons show a similar amount of haloing. The Sigma and the Nikon both look better wide open with a slight advantage for the Sigma in the DX-corner and the best FX-corner coming again from the Nikon.
Overall Tamron shows in this test a very good performance in the DX image-circle if you stop down just a little at the long end. Only the FF-corners look soft wide open and need stopping down to f5.6 if you need a well-balanced sharpness across the sensor.
Performance at long distances
The Siemens-star test-targets are shot at a distance of 50x focal length (i.e. at 2.5 m for 50 mm focal length). But performance of lenses also depends on the shooting distance. Therefore I present another series of test-shots of a city around 1 km away. Processing was done in Lightroom 6.12 from RAW at Adobe Standard settings. Noise-reduction is set to 0, sharpening to 50/0.5/36/10, 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. I used AF in live view at the largest aperture and did not change focus for other apertures.
First up is an overview of the wide-open performance at different focal lengths. You can jump to the detailed results at different apertures and comparisons with other lenses by clicking on the crops of the respective focal length. As usual I have selected the diagonal that provided the better corner results as almost any lens is a bit decentered.
In this long-distance test the new Sigma performs similar to the first test at closer distances: Very sharp in the DX image-circle with clearly softer FX-corners and a bit of haloing at the long end. If you want to see all the details and comparisons with the competition from Nikon, read on. Or fast-forward to the next chapter on vignetting.
The main image shows the complete scene wide open to give you an impression of the angle of view and to judge vignetting. All shots were made at ISO 64 and image stabilization switched off. Following the main image are 100% crops from the center, the APS-C/DX-corner and the FF/FX-corner at f2.8 from the new Tamron shot on a D850 and the Sigma 24-70mm f2.8 OS Art at f2.8 shot on a D810 at another day to compare performance and then from the new lens at f4.0 down to f11. Shooting the Sigma on a D810 makes the 100% crops a little less magnified. Still you can compare both lenses pretty good. As usual I have selected the diagonal that provided the better corner results as almost any lens is a bit decentered.
You can access all the large original images up to f11 via the links beneath the main image or by clicking on the respective crops. Please respect our copyright and only use those images for personal use.
Results at 24mm focal length:
Both lenses are very sharp at the center but the Tamron has a clear advantage in the DX- and FX-corner at 24mm.
Again, the Tamron is sharper in the DX- and FX-corner at 35mm.
The Sigma is now very close to the Tamron in the APS-C/DX image circle at 50mm. But the FF/FX-corner of the Tamron is still better.
Now the Sigma produces the punchier image in the DX image-circle while the Tamron looks a bit fuzzy due to haloing at f2.8. But it still has a slight lead in the FX-corner at 70mm.
In this long distance test the new Tamron repeats its very good performance in the DX image-circle from the first test. Just stop down a little at the long end for improved overall contrast. But if you need “sharp” in the outer reaches of a full-frame sensor you need to stop further down to f5.6 or even f8.0.
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 new Tamron and the Sigma at different apertures. All images were developed to the same brightness in the center. From left to right: f2.8, f4.0, and f5.6:
At 24mm the Tamron has slightly less vignetting than the Sigma especially when stopped down. At 70mm focal length both lenses look very similar with the Tamron retaining just a tad more vignetting at f5.6 than the Sigma.
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 the new Tamron, the Sigma, and the Nikon (shot at different nights) at various apertures:
The new Tamron produces quite a “spikey” coma in the FX-corner while coma of the Sigma is masked by the softness of the lens in the FX-corner. The Nikon in comparison is sharp and shows the typical signature of coma, albeit a very small one.
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.
And compared to the Sigma and Nikon:
The crops above show: The Tamron 24-70mm f2.8 VC G2 produces the softest Bokeh balls with only a weak outline. But there are some onion rings from its aspherical elements. The compression of the Bokeh balls towards the borders is similar to the Sigma and not as strong as with the Nikon. There is no clipping from the mirror-box.
Now let’s see how this analysis of out-of-focus point-light sources translates into Bokeh-performance shooting a book-shelf.
In this comparison the Tamron shows a harsher foreground and background than the Sigma. But the middle-ground of the Tamron shows a pretty smooth transition without coloration.
Flare, ghosting, and sun-stars
Catching a strong light-source shining directly into the lens is always a risky business. It could produce strange colorful ghost-images or reduce contrast considerably through flare and glare. The appearance of flare and ghosting depends on factors like the focal length, the aperture, and the angle of the light hitting the lens. So to judge the proclivity of the new Sigma 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 new Tamron does produce flare and ghosting when the light source is inside the frame (or just outside the FX-corner, see right image below) with the strongest effects occurring at the long end. You can also see that the sun-stars are not very well defined at f8 and 70mm focal length:
On the short end the lens behaves less critical and produces much nicer sun-stars (which improve further by stopping down). Still it shows some flares and ghosts when the light is inside the frame:
By comparison the Sigma shows slightly stronger artifacts and a prominent halo around dead-center lights but produces less glare, when the light source is just outside the FX-corner.
Next check out my sample images!Check prices on the Tamron 24-70mm f2.8 G2 at Amazon, B&H, Adorama, or Wex. Alternatively get yourself a copy of my In Camera book or treat me to a coffee! Thanks!