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 Sigma 105mm f2.8 DG DN Macro Art is practically free of loCA even when shot closer than my usual test distance. And there’s also no focus shift.
The following real life shot shows that the Sigma 105mm f2.8 DG DN Macro Art produces no purple fringing around high-contrast edges in the focal plane or green outlining around background subjects:
And there’s also no coloration around specular highlights as the image of the crumpled aluminum foil on the samples page shows.
Sharpness and contrast
Let’s have a look at the theoretical performance of the Sigma 105mm f2.8 DG DN Macro Art first and compare it to the Sony FE 90mm f2.8 G OSS Macro and Sigma 105mm f2.8 EX DG OS HSM Macro:
The MTF chart of the new Sigma Art looks promising, certainly better than from the Sony and Sigma HSM. [+]
These MTF charts show the computed lens-performance of lenses wide open without influence of diffraction at 10 line-pairs/mm (red) and 30 lp/mm (green). Higher values are better (more contrast) 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-corner), and 20 mm (FF-corner) on a on a 42MP Sony A7R II camera.
From the charts the new optical construction has lifted resolution and contrast of the Sigma 105mm f2.8 DG DN Macro Art compared to its DSLR sibling. It also should be sharper than the Sony wide open (green lines).
Let’s see how this theoretical performance translates into real life results in the sharpness test based on Siemens-stars. Processing was done in Lightroom 10.0/CRAW 13.0 from RAW to Adobe Color profile with the built-in lens profile for Vignette Control and CA compensation applied. Noise-reduction is set to 0, sharpening to 50/0.5/36/10, 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.
Performance of Sigma’s 105mm f2.8 DG DN Macro Art in the APS-C image-circle is already excellent at f2.8. Just the FF-corner is a little bit softer. The lens is so sharp indeed that you can see a very slight softening from diffraction already at f8.0. The test also showed very little field-curvature.
Performance at long distances
The Siemens-star test-targets are shot at a distance of 45x focal length (i.e. at around 4m). 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 10.0/CRAW 13.0 from RAW to Adobe Color profile with the built-in lens profile compensating vignetting and CA. Noise-reduction is set to 0, sharpening to 50/0.5/36/10, with no extra tone, color, or saturation adjustment. I used manual focus at the largest aperture and did not change focus for other apertures. All shots were made at ISO 100 and image stabilization switched off.
The following image shows the complete scene wide open to give you an impression of the angle of view. Following the main image are 100% crops from the center, APS-C-corner, and FF-corner from the new Sigma 105mm f2.8 DG DN Macro Art. As usual I have selected the diagonal that provided the better corner results as almost any lens is a bit decentered.
You can access the large originals but please respect our copyright and only use those images for personal use.
The overall contrast of the images is not very high but that is not the fault of the lens: the weather was overcast and humidity relatively high. Looking at the 100% crops though reveals an excellent level of fine detail even wide open. Stopping down to f4.0 of f5.6 just improves the FF-corner a tiny bit. Very good!
Vignetting and distortions
To make it easier to see light fall-off in the corners of a full-frame sensor I’ve arranged a series of shots with the Sigma 105mm f2.8 DG DN Macro Art at different apertures. All images were developed to the same brightness in the center.
The sample images above show that with the lens profile applied vignetting of the new Sigma relatively mild. Automatic shading compensation lifts the extreme corners about 0.5 EV at f2.8. Adobe’s RAW converter automatically applies shading compensation as it was set in camera – but you cannot alter the setting in postprocessing.
Distortions are of a very mild pin-cushion type at 2m distance. The setting for distortion compensation in camera is currently ignored by Adobe’s RAW converter and treated as OFF and there is also no lens profile for the new Sigma in Lightroom 10.0 / CRAW 13.0. This hopefully gets remedied in a later version. To get rid of the distortions you have to manually dial in a compensation of -2 in Lightroom. When shooting JPGs the camera at least does a pretty good job with Sigma’s lens profile to correct for distortions:
Distortions: Sigma 105mm f2.8 DG DN Macro Art, as is (top) / with lens-profile (bottom)
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 colour-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-corner of the new Sigma 105mm f2.8 DG DN Macro Art at different apertures compared to other lenses:
The Sigma 105mm f2.8 DG DN Macro Art produces very little coma even wide open.
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 crops below the main image are from the center, APS-C-corner, and FF-corner resized to make them comparable across all my reviews.
The diameter of the Bokeh balls in the center is determined by the entrance pupil of the lens. So the new Sigma should produce slightly bigger Bokeh balls than the Sony FE 90mm f2.8 G OSS Macro. Compression of the circle towards the corners looks relatively mild at f2.8 and is gone at the APS-C-corner at f5.6. But at that aperture the circle of confusion is no longer perfectly round in the center. The inside of the Bokeh balls is pretty smooth but there is some outlining. And again there’s no green coloration from longitudinal CA.
Now let’s see how this analysis of out-of-focus point-light sources translates into Bokeh-performance shooting a book-shelf. Crops are from the foreground, middle-ground, and background resized to make them comparable across all my reviews.
The Sigma 105mm f2.8 DG DN Macro Art produces a slightly nervous Bokeh in the foreground and background with some double-contours. Still the transition zone in the middle-ground is relatively soft and not at all marred by coloration from loCA.
The new Sigma Macro Art goes down to 1:1 magnification. The first set of images was shot at 1:3.4 magnification where the area of sharp focus is just 82 x 122mm. The crops shown below are from 4mm, 13mm, and 20mm off the center of the sensor respectively. For the following crops I focused once on the center at f2.8 and did not change focus:
The Sigma 24-70mm f2.8 DG DN Art produces very sharp results right across the sensor even at f2.8. Stopping down to f11 robs a bit of acuity due to diffraction.
The next set of images was shot from low ISO b&w film negativ at 1:1 magnification. So the “noise” that you see in the crops is actually the film grain. The crops shown below are from 3mm, 11mm, and 19mm off the center of the sensor respectively.
The new Sigma clearly out-resolves the target in this case even in the FF-corner at f2.8
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 aperture and the angle of the light hitting the lens. So to judge the proclivity of the new Sigma 105mm f2.8 DG DN Macro Art 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 mounted in all shots. Following are two of the more extreme example results. The little bright square inset in the upper left shows the respective area with an exposure compensation of +3 EV to make it easier to see which levels of black the lens renders at that point:
The Sigma 105mm f2.8 DG DN Macro Art produces some ghosting artifacts and overall contrast is reduced through veiling glare. To produce well defined sunstars the lens needs to be stopped down to f8.0 or below:
Next check out my sample images!Check prices on the Sigma 105mm f2.8 DG DN Macro Art at B&H, WEX, or Calumet.de! Alternatively get yourself a copy of my In Camera book or treat me to a coffee! Thanks!