About ISO 12233 Resolution Chart Image Quality Testing
What is an ISO 12233 Chart?
The ISO 12233 Chart is the I3A/ISO standard for measuring the resolution of electronic still imaging cameras. This site's tests utilize a large, costly, finely printed enhanced ISO 12233 variation, extending resolution to 4,000 lines per picture height (l/ph), along with other features.
To ensure that the chart remains perfectly flat, it is mounted on 1/2"-thick glass. To ensure that the chart does not fade, it is stored in a dark environment.
The test results of this chart serve as a great visual indicator of image sharpness (a combination of resolution and contrast), as well as lateral chromatic aberration (color separation in the periphery), and geometric distortion (influences the size of chart details).
About the Test Setup
If the test shots are not perfectly executed, the results are meaningless – or worse – deceptive. Thus, great pains are taken to ensure that the results are optimal.
To begin, the camera is mounted on a large, solid Manfrotto 400 Deluxe Geared Head mounted on a 158 lb (71.67 kg) Foba DSS-Gamma Studio Camera Stand. The camera stand is positioned on a custom liquid-leveled level, specially painted, 6" (152mm) thick concrete floor. Accurate camera and lens alignment on the test chart is critical, and multiple lasers are utilized for that task.
Lighting
To ensure accurate colors, the chart is lit by studio flashes. Another advantage of flash lighting is the short duration of the light — there is never a motion-blurred image.
Focusing
Accurate focusing is critical to achieving optimal results. Multiple focus strategies are utilized for each lens, including externally enlarged live view manual focusing. Each lens is tested many times (10+ to 15 or 20), and consistent results verify that optimal results have been captured.
Image Stabilization, if available, is turned off.
If the results are not as expected or show anomalies, other resources are contacted (including Roger Cicala at Lensrentals) and another copy of the lens is often tested.
Test Image Lens Settings
Image quality usually varies over the focal length of a zoom lens. So, 4 or 5 focal lengths are usually tested for each zoom lens. Selected focal lengths always include the widest and longest, along with a logical selection of marked lengths between.
If the lens is compatible with extenders/teleconverters, results with those mounted are included. Extenders are only desired to create longer focal lengths than a lens natively has, and thus, only the longest focal length on a zoom lens is tested with extenders. Extenders' additional lens elements and magnification always degrade image quality. This tool aids in decision-making in this regard.
Image quality changes with aperture, thus a range of apertures are tested for each focal length. Wide-open aperture image quality varies greatly, and most lenses produce their sharpest results at 1- or 2-stops narrower than their max opening. When the aperture becomes narrow, the effects of diffraction begin to soften the results. The site's testing standard is to test the widest aperture available at the focal length being tested, 1/3-stop narrower, and then all full-stop aperture settings through f/16. The f/16 results from all current and recent cameras show strong effects of diffraction, and the performance of most lenses begins to appear similar at this setting.
About the Test Image Processing
All test images are captured in RAW format. All aberration corrections are disabled in camera and during processing (review text will describe known forced adjustments).
The sharpness parameter makes a big difference in the results. Images from most cameras require some level of sharpening, but too-high sharpness settings (typically, manufacturer defaults), are destructive to image details and hide the deficiencies of a lens. The image quality results are lightly sharpened, and the site's standard sharpness settings somewhat align the results between manufacturers.
Canon images are processed in Canon's Digital Photo Professional (DPP) using the Neutral Picture Style, with sharpness set to 1 on a 0-10 scale.
Sony images are processed in Capture One using the Natural Clarity method, with the sharpening amount set to only "30" on a 0-1000 scale.
Nikon images are processed in Nikon ViewNX, with a sharpness setting of 0.
Contrast, saturation, and all other parameters are left at flat, low values. Images are converted into 16-bit TIFF files, and crops are created in Photoshop. The 100% resolution JPG format crops shown in the tool are created using PS's Save for Web processing. A JPG quality setting of 70 keeps the files reasonably small for fast web page loading but with no compression artifacts showing.
Why Were These Crop Sections Selected?
The "Center" crop (1 on the chart above) shows a pattern that is slightly to the right of the chart's center. Most lenses are sharpest in the center of the frame.
The "Mid-Frame" crop (2) from a full-frame camera represents a near-corner on an APS-C (1.5x or 1.6x field of view crop factor) camera body.
The "Periphery" crop (3) is from an area near the top-right corner of the image. Light rays are refracted to a stronger angle in the periphery of the image circle, and image quality tends to degrade toward the periphery. The flat test chart will also show highlight field curvature, the optimal focus distance changing throughout the image, an aspect that I never want.
The "Corner" crop (not available for all lenses) usually shows the absolute worst performance of the lens.
When ultra-high-resolution cameras were introduced, interesting details were cropped from the results. Thus, a second set of "Center", "Mid-Frame", and "Periphery" crops were added below the original set.
Remember that your subject will often be positioned away from the center of the frame. View the test results while considering your needs.
Use the Comparisons
Any lens, camera, focal length (including with extenders), and aperture combination tested can be compared to any other. Select the first test on the left and the comparison test on the right.
You will see the test results selected on the left until you hover your mouse over the result images (or the arrow). Moving the mouse back and forth toggles the results. This is my favorite way to visually compare lens and camera test results. You can even compare a lens to itself to learn more about its performance.
Additionally, the arrow buttons between the lens models can be clicked to lock the displayed results (ideal for mobile device users).
Remember, looking at 100% crops from high resolution cameras is like viewing a huge enlargement from a close distance. This chart, the low amount of sharpening, and the low contrast processing is unforgiving to a lens. You should expect real world images to look at least as good – often better.
This Tool Needs Your Support
Obviously, I have invested a huge amount of time and money in this project, and I hope to contribute to the photography community by making camera and lens selection easier.
That said, I need your support.
Sharing the site is one form of helpful support. The comparison pages are coded to allow sharing a link to a specific comparison (share the link as the social sharing buttons tend to miss the settings).
I always appreciate suggestions and comments.
Go to the Lens Comparisons.
