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 Samyang shows some mild loCA wide open but by f5.6 it is gone. The test also revealed that there is no relevant focus shift.
The Zeiss is a bit less well corrected especially at f2.8 in the magenta foreground:
Shooting at closer distances (around 1m) normally aggravates any loCA problems. See the Samyang in the following 50% crop on top and the Zeiss at the bottom – both lenses shot at f2.0:
Both the Samyang and the Zeiss behave well for such a close distance.
Sharpness and contrast
Let’s have a look at the theoretical performance of the Samyang first compared to the performance of the Samyang 135mm f2.0 ED UMC:
These charts show the lens-performance of both lenses at their largest aperture f2.0. But while most manufacturers like Samyang (on the left) display the contrast-curves at 10 lp/mm and 30 lp/mm Zeiss displays the contrast-curves at 10, 20 and 40 lp/mm (from top to bottom), which is a bit unusual. To read these charts you need to know that higher values are better and the closer the line-pairs (dotted and continuous for Zeiss, dark and light color for Samyang) 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 D810.
From the charts, the Samyang should outperform the Zeiss: The 10 lp/mm contrast of the Samyang is above the Zeiss and the 30 lp/mm contrast of the Samyang is even higher than the less demanding 20 lp/mm contrast of the Zeiss. Both lenses show very little decline in sharpness towards the corners of the sensor and little sign of astigmatism – at least on paper. You should be aware that manufacturers produce MTF charts in different ways: Some measure the MTF on a real lens (like Zeiss does) some use calculated MTF values that come out of the lens design software. So it’s crucially important to 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 6.6 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.
The following are all 100% crops!
These 100% crops directly from a 36MP D800 sensor shows an excellent performance of this lens right from f2.0 and all across the full-frame sensor. This is very impressive indeed! With such a sharp lens you can see signs of diffraction setting in ever so slightly at f8.0 and clearly at f11. Distortions are very low.
Following is a direct comparison of the Samyang (1st row) to the Zeiss (2nd row):
The Samyang and the Zeiss perform pretty similar at a very high level with the Samyang showing a little less spherical aberrations in the center. At the APS-C/DX-corner the Zeiss is in the lead. And at the FF-/FX-corner both lenses are hard to distinguish: both produce stunning results at the outer area of the sensor. Regarding field curvature at this distance: The crops of the Zeiss were all taken from the same shot while the Samyang needed a bit of focus optimization indicating a slightly curved field.
Performance at large distances
The Siemens-star test-targets are shot at a distance of 40x focal length, which is in this case 5.4m. But performance of lenses also depends on the shooting distance. Therefore I do another series of test-shots of a landscape dubbed the “Unremarkables” where you can measure distances in km, not meter. I use this scene to show you how the lenses perform when almost everything is at infinity. I set White Balance to a standard daylight value to make them comparable across lenses shot at the same day and also try to make exposure comparable. There’s no tinkering with vignette-control so you see it here as it is produced by the lens. Focus was manually acquired at the largest aperture in live-view and not changed for other apertures.
You can click on the 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 maximum aperture to give you an impression of the angle of view and to judge vignetting. This is followed by one row of 100% crops from f2.0 to f11 each from the middle, the APS-C/DX-corner and the right FF/FX-corner.
You can access the respective shots up to f22 via the links beneath the main image.
Performance at long distances confirms the tests at 5m: This lens is very good even wide open in the APS-C/DX image-circle and astonishingly good in the FF/FX-corner. Only the amount of vignetting is a bit of a let-down. Stop down to f4.0 to get superb clarity across the sensor and very low light fall-off. I shot the same scene within minutes with the Zeiss 135/2.0 Apo Sonnar for comparison:
In the center and the APS-C/DX-corner both lenses perform almost identical. Only in the FF/FX-corner the Zeiss has a small lead. Maybe the lower field curvature of the Zeiss pays off here.
Want to see how much clearer the image of the fixed focal lens is (be it Zeiss or Samyang) compared to a professional-grade zoom lens like the Nikon AF-S 70-200/2.8G VR II? Head over to my Zeiss 135mm f2.0 Apo Sonnar review. Even with the zoom at f8 does it not completely reach the contrast and resolution of the fixed focal at f2.8.
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 Samyang (1st row) and the Zeiss (2nd row) at different apertures. From left to right: f2.0, f2.8, and f4.0:
As you can see, the differences under controlled conditions are negligible wide open. At f2.8 the Zeiss is a bit darker in the extreme corners while at f4.0 the Zeiss pulls ahead with very little light fall-off.
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 Samyang at various apertures:
Both the Samyang and the Zeiss (following crops) show a near identical performance with almost no coma. Very good!
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.
The Samyang produces nice smooth Bokeh balls with little outlining but it exhibits a clear cat’s eye effect towards the corners. There is only slight clipping from the mirror-box at the extreme bottom of the image. Let’s see how the Zeiss compares:
The Bokeh balls in the center of the Samyang are a bit smaller than from the Zeiss but the cat’s eye effect towards the corners is less pronounced. So in the FF/FX-corner the Samyang effectively has the larger Bokeh balls than the Zeiss. Inside the circles of confusion the Samyang also has a smoother appearance than the Zeiss. The Zeiss shows the same slight clipping as the Samyang. This shot is also available at f2.8, f4.0, f5.6, 8.0.
Now let’s see how this analysis of out-of-focus point-light sources translates into Bokeh-performance shooting a book-shelf.
The (less important) foreground has a busy Bokeh. But the middle ground shows a smooth out-of-focus transition and stays clean of color artifact often seen with other large aperture lenses. And the background Bokeh is pretty creamy. Let’s see how the Zeiss compares:
The Zeiss renders the foreground softer than the Samyang. But in the middle-ground and the background the Zeiss cannot match the creamy blur of the Samyang. This shot is also available at f2.8, f4.0, f5.6, f8.0.
BTW.: If you want to know how the Nikon AF DC 135/2.0D compares with respect to sharpness, loCA, and Bokeh head over to the results section of my Zeiss 135mm f2.0 Apo Sonnar review.
A strong light-source shining directly into the lens 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 Samyang for these artifacts I went through a series of well calculated shots against a strong light source to provoke flare, glare, and ghosting.
At f2.0 I found a little glare, but nothing too worrying. Closed to f8 the lens produced some flare when the light was inside the image circle (see left image below) and some glare, with the light some degrees outside the image circle (right image below). These results are pretty good and better than from the Zeiss 135/2.0.