About ISO 12233 Chart Data and Sample Images
What is an ISO 12233 Chart?
The ISO 12233 Chart is the I3A/ISO standard for measuring the resolution of electronic still imaging cameras.
The chart I am using is a very expensive, finely printed variation of the ISO 12233 standard
that extends resolution to 4,000 lines per picture height (l/ph) and features other benefits as well.
This chart serves as a good visual indicator of sharpness as well as CA (Chromatic Aberration) and distortion.
About the Test Shot Setup
If the test shots are not perfectly executed, the results are meaningless - or worse - deceptive.
I go to great pains to make sure the test images are accurate:
The camera is mounted on a very expensive (and very nice) Arca-Swiss C1 Cube geared head which is mounted on an 145 lb (65.8 kg) Bogen / Manfrotto 809 Salon 230 Camera Stand.
The camera stand is positioned on a custom designed, perfectly level, specially painted, 6" (152mm) thick concrete floor.
The camera/lens is multiple-laser-aligned to the target which is mounted on 60" (1524mm) square, 1/2" thick glass.
Focus assit lighting is from 2 Solux continuous lights.
Primary light is provided by 4 Canon 580ex II Speedlites.
I've tried many other lighting solutions, but this is the one that provides clearly the best results.
Tests are conducted using center-point-only autofocus and Live View manual focusing.
The best of the many re-focused shots (typically at least 10 sets - often 15-20) are used for the results for each camera/lens/focal length/aperture combination.
The proper lens hood is in place for all test shots, all filters are removed.
Image Stabilization, if available, is turned off.
About the Shot Settings
All test shots are taken in RAW format using Canon's Neutral picture style (all parameters = 0).
Using DPP (Canon's Digital Photo Pro), a sharpening setting of 1 is added.
The sharpness parameter makes a big difference in the results.
I chose a setting of 1 because it is the minimum setting I use in my real world shots.
It is, however, very weak sharpening.
Keep this in mind when viewing the results.
Contrast, saturation and all other parameters are left at flat 0 / neutral values.
Pictures are converted into 16-bit TIFF files for processing.
Why Were These Crop Sections Selected
The top 100% crop (1 on the chart above) shows a pattern that is slightly to the right of center - for evaluation of the center performance of the lens
(typically the sweet spot).
The middle 100% crop (2 above) is taken from the position that when shot on a full frame body represents a corner on a
1.6x FOVCF camera body.
The bottom 100% crop (3 above) is from an area near the top-right corner of the image - regardless of which FOVCF body took the shot.
Keep in mind that your subject will very frequently not be in the center of the frame (many use the rule of thirds for their composition).
Why Do the Pattern Sizes Vary
While I go to great lengths to get perfect test shots, there may be slight variations.
I do not think these variances are enough to sway the comparison - otherwise I reshoot the test.
Still, some graphics in the test crops still vary in size.
What you may be seeing is lens distortion.
Strong barrel distortion will typically make the pattern in the top crop appear larger - pincushion distortion will have the opposite effect.
Why Does The Bottom Crop Sample Vary in Brightness?
Variances of brightness in the bottom crop sample can be attributed to two things.
First, at wide apertures, the difference is usually light fall-off/vignetting.
This difference is very helpful to see and compare.
At narrow apertures, where light fall-off is no longer an issue, the power of my flashes must be turned up dramatically.
It is very hard to illuminate the chart perfectly evenly at this flash power level and the corners may be slightly brighter due to light fall-off across the chart from the flashes.
Also, even though the lights are close to the test target plane, reflections are still a problem when testing super-wide angle lenses.
I've implemented a newly-available larger test chart in 2008 to help with this issue.
Are The Crop Samples Accurate Image Quality Indicators?
For the most part, I find the results to be very indicative of the image quality of the lens being tested and the comparisons work very well - the results are even better than I had hoped for.
However, there are a few lens with results that I'm not totally satisfied with.
The Canon EF-S 17-55mm f/2.8 IS USM Lens and
Canon EF 24-105mm f/4 L IS USM Lens
do not seem to like the close subject distances - they under-performed in the comparison tool.
And the cheap Canon EF-S 18-55mm f/3.5-5.6 IS USM Lens
performed better the wider focal lengths at the relatively short distance than I would expect to see from this lens - it over-performed in the comparison tool.
How To Get the Most Out of the Comparison
Any lens/camera/focal length/aperture/extender 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 - then the compare-to test results appear.
Moving the mouse back and forth toggles the results - my favorite way to visually compare lens and camera test results.
You can even compare a lens to itself.
Lenses should be compared to each other only with test data from the same camera body as it is the combination that is tested.
Sample images taken with the Canon 40D,
Canon 30D and
Canon 400D/Rebel XTi
are framed very slightly wider than those from the Canon EOS 1Ds Mark II.
Since their viewfinders do not show 100% views (about 95%), the 40D, 30D and 400D/XTi cameras require the zoomed LCDs to be used for framing.
Since their LCDs show only about 98% of the shot, this is the final framing used for these sample shots.
The Canon EOS Rebel XSi/450D is slightly better, showing about 99%.
The Canon EOS 1D Mark III and
Canon EOS 1Ds Mark III
viewfinders are just-slightly less than 100% and the LCD shows about 99.6% of the final image during review.
Note: Zoomed LCD review is used for all final framing.
Remember, looking at 100% crops from these high resolution cameras is similar to viewing a huge enlargement from a close distance.
This chart is tough on a lens - You should expect real world images to look at least as good - and likely better.
Share the Comparisons
The comparison pages are coded to allow saving and sharing a link to a specific comparison.
This feature should be especially helpful to the many valuable forums discussing such information.
Some Final Words ...
Obviously, I have invested a huge amount of time and money in this project.
It is my hope that I can contribute to the photography community by making lens selection easier.
I always appreciate suggestions and comments.
