Canon EF-S 18-135mm IS Vignetting / Light fall-off
|To measure the Canon EF-S 18-135mm IS’s vignetting and light fall-off we photographed a white target with a highly diffused filter. The lens was manually focused to infinity and tested at its shortest and longest focal lengths with its aperture wide open. The images were shot in RAW mode to avoid any in-camera corrections, then analysed with Imatest and the full areas presented here at a reduced resolution. This time, bigger percentages are better. Results for other general-purpose lenses are shown at the bottom of this page; note the results for the EF-S 18-55mm here are for the older non-IS version.|
Zoomed-out to 18mm and with its aperture wide open, light falls-off in the corners of the frame to 53.2% of the centre measurement. This results in quite noticeable darkening in the corners of uncorrected images, although it’s by far not the worst of the Canon general-purpose zooms tested here.
The EF-S 15-85mm IS USM, despite its higher price and status suffers from noticeably worse darkening in its corners with a measurement of 42.1%. Perhaps less surprisingly the EF-S 18-200mm IS super-zoom does worst of all with a measurement of 37.7%. Interestingly the older EF-S 17-85mm IS USM performs better than its successor in this regard, and edges ahead of the EF-S 18-135mm IS, although again the best result comes from the EF-S 18-55mm kit lens. Yes it’s the cheapest, but by sporting a modest range, it manages to avoid many of the optical artefacts which plague longer zooms.
Luckily all the lenses greatly improve with their apertures closed to f8, and vignetting is also an effect which can be corrected fairly effectively in software with DPP, or in-camera on models which support Peripheral Illumination Correction. Indeed if you don’t adjust the settings on a new Canon DSLR, you may rarely notice much darkening in the corners with any of these lenses as Peripheral Illumination Correction is normally enabled by default. Disable it or use an older model though and the darkening will become apparent in the corners at large apertures.
Zoomed-into 135mm with its aperture wide open, light falls-off in the corners to 63.8%, which is worse than any of the other lenses tested here apart from the EF-S 18-200mm IS super-zoom. Again this is something you’d expect given their longer focal ranges, although it’s reassuring to find the EF-S 15-85mm IS USM performing more respectably when zoomed-in than the poor result measured when zoomed-out.
So once again you’ll notice some darkening in the corners of uncorrected images, when the aperture is wide-open, although again this can be greatly reduced by closing the aperture to f8, or applying correction, either in software or in-camera (where supported).
But like geometric distortion, vignetting is another optical issue which faces the EF-S 18-135mm IS. It’s one of the prices you pay for an affordable lens with a long focal range, although at least this time it’s fairly easy to correct.
That’s enough for our formal tests now, so let’s check out some more real-life sample images in our Canon EF-S 18-135mm IS Gallery.
Canon EF-S 18-135mm IS Vignetting / Light fall-off compared to other lenses