Do You Know What We're Looking At?
If you are not familiar with vignetting, please read the Canon Lens Vignetting (Light Fall-off, Peripheral Shading) page to gain understanding of what attributes I am reviewing.
Using the F-stop Contour Plot Vignetting Test Results Tool
Any lens/camera/focal length/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 image – then the compare-to test results appear. Moving the mouse back and forth toggles the results – my favorite way to visually compare lens test results. You can even compare a lens to itself at different settings.
Test Shots "With UV/CP Filter"
The test images for a lens wider than 40mm often include set captured with a normal thickness B+W brand UV/clear and circular polarizer filter in place. The with-filter test results are captured at a lens' widest focal length and presented last in the focal length list. Compare these results with the results from the same focal length/aperture without the filter attached to look for mechanical vignetting caused by these normal-thickness filters. A slim version of the filter is required if the corner shading increases more than you are comfortable with.
What Is The Small Gray Frame In The Vignetting Sample Pictures?
The small gray frame seen in full frame lens results represents the APS-C/1.6x Field of View Crop Factor (FOVCF) found in many of Canon's Digital SLR Cameras. Nikon's APS-C sensors have a 1.5x FOVCF, so the APS-C frame is shown slightly tight for the full frame Nikon lenses. If you are using one of these camera bodies (and don't plan to move to a full frame body in the near future), you can disregard the vignetting results outside of the gray frame – where it is strongest.
Norman Koren's Imatest is used to plot the f-stop contours on the contour results. Pay attention to the f-stop numbers more than where lines are present on these images. The numbers are what matter as some plots include more/fewer lines which appear at different frequencies.
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