This comparison is to test a group of lenses I have for lateral chromatic aberrations or CAs, also called purple fringing, at 1X of life-size magnification. The reason that I spend the time to run a test like this is simply to find out how my lenses perform and to share the results since testing for this. There are thousands of CA tests online but they don't run their tests at close up distances so this is the only 1X CA test online as far as I know.
What are Chromatic aberrations (CAs)
Chromatic aberrations (CA) are one of several aberrations, or imperfections, that degrade image quality. These occur because glass bends different colors by different amounts. This phenomenon is called dispersion, and this is why you see some high performance lenses have labels such as, SD, UD, ED, SLD, ULD. These acronyms all refer to different types of low-dispersion glass types used in the lenses.
Lateral CAs appear in images as purple and green fringing, mostly seen on near-vertical hard edges on the left and right corners of the image. This results in softening of edges in the corners of an image. CAs occur because the different wavelengths of light are magnified by slightly different amounts by the lens.
Minimizing chromatic aberration is one of the most important goals of a lens manufacturer. Lens design correct for CAs by combining different lens elements with different dispersion properties, or different refractive indexes. But CAs remain a big problem for lens manufacturers in ultra-wide lenses, long telephoto lenses, and extreme zooms. Most manufacturers offer some level of correction, some can completely correct CAs, with in-camera correction. Over the last few years some manufacturers have become really sneaky with the use of Opcodes.
According to Adobe, companies like Sony, Olympus, Leica, and Panasonic tag RAW files with Opcodes to remove chromatic aberrations. The sneaky part is that Opcode force corrections in Lightroom and Adobe Camera Raw before you even even open the image. Opcodes cannot be disabled but you can delete the codes with certain apps. Opcodes also corrects for distortion (and vignetting) which means the image will be enlarged slightly then cropped to correct for distortion so there could be some effect on sharpness.
Lateral chromatic aberration is reduced by the lens design to a certain degree by combining different lens elements with different refractive indexes. There are lenses that use very complex designs using expensive low-dispersion glass to completely eliminate CAs. Examples of these types of lenses would be the Printing Nikkor, Scanner Nikkor and Schneider Macro Varon.
D810 camera was mounted on a Newport PRC-3 rail carrier and Arca Swiss style quick release clamp and moved back and forth to accommodate the different focal length lenses set at 1X. The Newport PRL dovetail rail system was bolted to a Thorlabs aluminum breadboard. The laser printed test target was taped to a Newport 460P XYX micrometer controlled setup. A single Nikon SB-R200 flash was used for lighting and has bolted to a articulating flash arm.
Why doesn't my lens show the same amount of CAs as your lens?
A test like this, with a high-contrast test target, will reveal chromatic aberration much more strongly than a real world in-the-field macro image. There are a few factors why you might not see the same CAs on your lens.
-You never tested for CAs.
-Your DSLR is removing CAs automatically in camera.
-Your RAW convertor is removing CAs before you even open the RAW file. Cameras from Sony, Olympus, and Panasonic use Opcodes to force CA removal automatically with Lightroom and ACR . See this link for more info.
-There are psychological factors, such as denial for some owners of expensive legendary APO lenses, like the APO-Lanthar, that is supposed to be CA free, only it's not.
This is the full frame un-cropped target showing the test crop area. Crops are all 200% actual pixel view in Photoshop.
Sigma 70mm F2-8 EX DG Macro
Rodenstock 75mm f4 APO-Rodagon D
Schneider Macro Varon CAS 85mm f/4.5
Nikon Scanner ED Nikkor ED 100mm
Nikon AF-S VR Micro-NIKKOR 105mm f/2.8G IF-ED
Sigma 105mm f2-8 EX OS Macro
Voigtlander 125mm f2-5 APO-Lanthar
Sigma 150mm f2-8 EX OS APO Macro
Sigma 180mm f2-8 APO EX OS Macro
Nikon AF Micro-NIKKOR 200mm f4D IF-ED
There is a hint of CAs wide open at f/2.8 but the Sigma 70 is very clean at f/5.6 and smaller.
The Rodenstock 74mm 1:1 crop is very clean and very sharp.
The Macro Varon and the Scanner Nikkor are totally CA free.
The Nikon 105 VR has the worst CAs in this test. The Sigma 105 even with CAs looks great next to the Nikon.
The APO-Lanthar obviously not an APO, but neither is the Sigma 150, although Sigma did a much better job elimiating lateral CAs with the 150.
The Sigma 180 CAs get worse as it is stopped down, no its not an error, I double checked the files.
The Nikon 200 is pretty clean at f/4 but the CAs, like the Sigma 180, increase at smaller apertures.