Testing: Longitudinal Chromatic Aberration and focus shift
Lenses with focal ratios of f2.8 or larger are often prone to longitudinal color aberrations (loCA, a.k.a. “axial color” or “bokeh CA”). These show up as magenta coloration in the foreground and greenish hues in the background and are not easily corrected in post-processing. The new Nikon shows no loCA at all.
But there is quite some focus shift when you stop down: the background becomes sharper pretty fast while the foreground becomes less sharp. This can be quite annoying when you focus wide open and shoot stopped down – as you normally do. Dialing in some slight front-focus at f2.8 helps a bit. At 150mm focal length the focus shift is gone.
Its predecessor, the Nikon 70-200/2.8G VRii, shows no discernible focus shift at 200mm and also very little loCA:
Sharpness and contrast
Let’s have a look at the theoretical performance of the new lens (first pair of MTF-charts) at the wide and the long end first and compare it to the performance of its predecessor the Nikon 70-200/2.8G VRii (second pair of MTF-charts):
These charts show the lens-performance 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 (DX-corner), and 20 mm (FX-corner) on a D810 below.
From the charts, the new Nikon should be the better performer as its lines almost always stay above the respective curves from its predecessor. 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 DX-corner results and FX-corner results on a D810. Processing was done in Lightroom 6.6 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 of all crops match. So you will not see light fall-off in the corners. CA-removal is ON. In my comparative shots with the Sigma and the Tamron below I set sharpening to 70/0.5/36/10 to compensate for the slightly softening effect of the AA-filter of the D800 which was used for those shots.
The following are all 100% crops!
Let’s have a look at the performance at 70mm focal length first:
Following is a comparison with the competition at 70mm, f2.8:
The new Nikon tops the other lenses clearly. It’s super sharp in the DX image-circle and only a bit soft in the FX-corner.
Performance at 102mm:
Following is a comparison with the competition at 105mm, f2.8:
At 102mm focal length the FX-corner of the new Nikon becomes a bit softer but the DX image-circle stays on an excellent level. Its predecessor, the Nikon 70-200/2.8G VRii is becoming quite soft from aspherical aberrations although fine details still come through.
Performance at 150mm:
Following is a comparison with the competition at 150mm, f2.8:
At 150mm the FX-corner of the new Nikon comes back to good performance again. Only the Tamron can keep up at this focal length.
Performance at 200mm:
Following is a comparison with the competition at 200mm, f2.8:
At 200mm the new Nikon softens just a little in the center (shown at 4mm off axis here) and its predecessor is actually a bit sharper. But looking further away from the optical axis the new Nikon re-establishes its lead over all competitors. There’s also some focus-shift that can be observed in the center: stopping down from f2.8 to f5.6 gradually makes the center a little less sharp.
Overall Nikon’s new design proves to be very good within the DX image-circle even wide open. There is the expected roll-off in sharpness towards the edges of a full-frame sensor that is strongest at 105mm focal length and only marginal at 70mm and 150mm. At 200mm sharpness in the FX-corners is excellent. The new lens bests its competition including its predecessor at all focal lengths across the sensor were it not for the slight softness in the center at 200mm where it’s predecessor delivers a better performance. Still a very impressive feat!
Performance at long distances
The Siemens-star test-targets are shot at a distance of 40x focal length (i.e. at 8 m for 200 mm focal length). But performance of lenses also depends on the shooting distance. Therefore I present another series of test-shots of a city-scape around 2km away. Processing was done in Lightroom 6.6 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. I used AF in live view at the largest aperture and did not change focus 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 f2.8 to give you an impression of the angle of view and to judge vignetting. You can access the respective shots up to f16 via the links beneath the main image. All shots were made at ISO 64 and VR switched off. Following the main image are 100% crops from the center, the DX-corner and the FX-corner from the new Nikon and its predecessor at f2.8 to compare performance and then from the new lens at f4.0 down to f11. The shots with the 70-200/2.8G VRii are from another day but with similar atmospheric conditions
Let’s start with 70mm focal length:
The new lens bests its predecessor at the center and the FX-corner.
Results at 105mm:
Clear advantage for the new lens in the center.
Results at 150mm:
150mm is the really weak spot of the older 70-200/2.8G VRii lens. It’s no match for the new design in this comparison.
Results at 200mm:
Similar performance of both lenses within the DX image-circle. But the improvement in FX-corner performance of the new lens is glaringly obvious.
The crops from the center of the new lens at f4.0, f5.6 and f8 are actually less sharp than the crop at f2.8. This matches the observation from the Siemens-star test-shots above.
In this long distance test the new lens again showed it’s merit with a much improved performance especially in the middle of the zoom range (105mm and 150mm) over its predecessor.
Long-distance performance with teleconverter
Let’s see how the lens performs with the Nikon TC1.4xIII teleconverter attached. These shots are from another day but with similar atmospheric conditions. Following is the performance at 200mm for comparison with the original performance without tele-converter and at 280mm. As usual you can click on each crop to access the large original.
Results at 200mm (with the lens itself set to 140mm):
With the tele-converter attached the new lens outperforms its predecessor by a huge margin at 200mm. But compared to the results without TC at 200mm the new lens stopped down to f4.0 actually is less sharp w/o tele-converter than with TC. A result of the slight softness in the center at 200mm and the focus-shift from stopping down to f4. The shot from the Nikon 70-200mm f/2.8G VRii with TC 1.4xIII at 200mm is also available at f5.6, f8.0, and f11.
Results at 280mm (with the lens itself set to 200mm):
Both lenses perform pretty similar with TC at 280mm with a slight advantage for the new 70-200/2.8E VR. The shot from the Nikon 70-200mm f/2.8G VRii with TC 1.4xIII at 280mm is also available at f5.6, f8.0, and f11.
Stopping down doesn’t improve performance of the new lens (except for light fall-off). Again probably a result of the focus-shift at the long end.
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 70-200/2.8E VR (1st row) and the old 70-200/2.8G VRii (2nd row) at different apertures and 200mm focal length. From left to right: f2.8, f4.0, and f5.6:
That’s interesting: at f2.8 the new lens has a higher vignetting than the old one but the situation is reversed when stopping down. At f5.6 the new lens is practically free of vignetting while the old still has visibly darker corners.
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 70mm focal length and various apertures:
The new lens delivers very little coma at f2.8 especially compared to its predecessor (see below). From f4.0 onwards coma is of little relevance.
Rendering of out-of-focus point-light sources and Bokeh
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 Nikon 70-200/2.8E VR produces pretty big Bokeh balls when used wide open. It exhibits no onion rings and the light-distribution across the circle is very even. Outlining is moderate and shows no green coloration from loCA. There’s an obvious cat’s eye effect which reduces the size of the Bokeh balls towards the corners and may generate some nervousness in out-of-focus areas there. The lens produced no clipping from the mirror-box at the top or bottom of the image. The predecessor does not show much of a difference:
Now let’s see how this analysis of out-of-focus point-light sources translates into Bokeh-performance shooting a bookshelf. I used the longest focal length that I could to produces a comparable shot to my other reviews which was in the case of the new Nikon 150mm:
Let’s see how the Nikon 70-200/2.8G VRii compares. To achieve the same magnification as before I had to zoom in 10% further than above to 165mm focal length. A consequence of the much discussed “shrinking” design of the old zoom:
Comparing both the new lens is a bit softer in the foreground but just a tad more nervous in the background. In the transition-zone just behind the plane of sharpest focus the new lens has the slight benefit of a somewhat softer transition with no coloration from loCA. But in practice I doubt that you will often see any relevant differences.
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 new lens is pretty prone to flare and glare. Especially on the long end having a strong light-source inside or even just outside the corner of the frame (see image on the right below) should be avoided as veiling glare and ghosting heavily reduces the contrast:
On the short end the lens behaves less critical and maintains overall contrast much better. Still it produces clearly visible flares and ghosts when the light is inside the frame. Following are two of the more extreme effects:
In most situations though the new lens is better behaved than its predecessor.
Support Cameralabs when you check prices at Amazon, B&H, Adorama, eBay or Wex. Alternatively get yourself a copy of my In Camera book or treat me to a coffee! Thanks!