I use Imatest to undertake all lens evaluations.
My approach is to perform the test (sharpness and CA only), publish the data and leave readers to draw their own conclusions. Readers can add comments to aid discussion, feel free to post your comments!
Method
Wherever practical, tests are undertaken by photographing an ISO 12233 target with a Canon EOS 20D at ISO 100 set on RAW mode. For wider angle lenses a combination of targets are used.
No in-camera processing is performed. The camera is placed on a tripod, mirror lock up is set and a remote release is used for capture.The resultant RAW images are then converted to 16bit TIFFs using RSP 2006 set at -15 sharpness bias with checkbox unchecked, this approximates to using CS RAW importer with sharpness 25 and Capture One with sharpness settings (soft look 20).
All tests are performed and compiled by EOS-Images within the same environment.
Information is provided as-is and no guarantee or claim is made as to its accuracy, however all data is copyright EOS-Images.com.
Interpretation of results
Sharpness
The graph depicts two or three bars per aperture. Each bar represents a region of interest (ROI) taken from the target frame e.g. Centre, Edge and Extreme Edge. The value unit is line width per picture horizontal. i.e. the higher the value, the more lines recorded per horizontal frame, hence the sharper the lens. In general, values >1800 lw/ph are excellent and values <1000 lw/ph are poor.
Chromatic Aberration
The graph depicts one or two bars per aperture. Each bar represents a region of interest (ROI) taken from the target frame e.g. Edge and Extreme Edge. The value unit is area width in pixels i.e. the lower the value the less area width of pixels visible, hence lower chromatic aberration.
In general, values >2 pixels are poor.
Try not to read too much from the actual numbers when comparing data with other sites. Environment, exposure, lighting and post processing all play a significant role in lens evaluation. I therefore recommend that readers looks at the profile of the curve. That way you will get a more objective view of its performance.
Notes:
- Centre has ROI within ~10% of centre of frame.
- Edge has ROI ~60% left or right of centre of frame.
- Extreme Edge has ROI ~85% right of centre of frame.
- CA has ROI ~60% left or right of centre of frame.
- The EOS20D resolves to a maximum of ~2050 lw/ph
Finally, if you have a lens that you wish to loan for an afternoon then drop me an email, I’d love the opportunity to add it to the list!
