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. 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. Lenses such as Canon EF-S Lenses only fill this inner frame with sample image. Nikon’s APS-C sensors have a 1.5x FOVCF, so the APS-C frame is slightly tight for the full frame Nikon lenses. Imatest 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. Back to the Lens Comparisons.
