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Canon EF-S 15-85mm f3.5-5.6 IS USM Gordon Laing, February 2010
 

Canon EF-S 15-85mm IS USM results : Sharpness 15mm / Sharpness 50mm / Sharpness 85mm / Geometry / Vignetting


Canon EF-S 15-85mm IS USM Vignetting / Light fall-off

To measure the Canon EF-S 15-85mm IS USM'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.


Canon EF-S 15-85mm IS USM vignetting zoomed-out
 
Canon EF-S 15-85mm IS USM vignetting zoomed-in
EF-S 15-85mm IS USM at 15mm f3.5
Mean corner fall-off: 42.1%
EF-S 15-85mm IS USM at 85mm f5.6
Mean corner fall-off: 69.8%


Zoomed-out to 15mm and with its aperture wide open, light falls-off in the corners of the frame to 42.1% of the centre measurement. Measurably worse than most of the Canon general-purpose zooms, vignetting at wide-angle is the Achilles' heel of the EF-S 15-85mm IS USM. Disappointingly it's both measurably and visibly worse than its predecessor, the EF-S 17-85mm IS USM, itself no angel in this regard. It's even a little worse than the 46.8% measured for the EF-S 17-55mm IS USM when zoomed-out, despite its brighter f2.8 aperture, and comfortably worse than the 53.2% measured for the low-priced EF-S 18-135mm IS.

In its defence though, the wide-angle vignetting of the EF-S 15-85mm IS USM is not the worst of the Canon general-purpose lenses. The EF-S 18-200mm IS super-zoom really suffers with a mean corner fall-off of 37.7%. It's also important to note the EF-S 15-85mm IS USM boasts comfortably wider coverage than any of the other lenses here, and with Peripheral Illumination Correction enabled (in-camera or through DPP), the figure became a much more respectable 79.9%.

The bottom line though is darkening in the corners can be quite apparent on uncorrected images with the EF-S 15-85mm IS USM when zoomed-out, and you'll even see it in the viewfinder when composing a shot which contains flat areas of colour like a blue sky. You'll also notice it darkening the corner crops on our uncorrected real-life results pages, albeit becoming much reduced as the aperture is closed to f8.

Zoomed-into 85mm with its aperture wide open, light falls-off in the corners to 69.8%, and while this is worse than the 77.5% measured for the older EF-S 17-85mm IS USM, it's not as big a problem as when zoomed-out. It's also slightly better than the 63.8% figure measured for the EF-S 18-135mm IS when zoomed-in, and all the lenses here do considerably better than the poor 41% score of the EF-S 18-200mm IS when zoomed-in. But once again, darkening in the corners of the EF-S 15-85mm IS USM when zoomed-in can be apparent on uncorrected images, and also through the viewfinder when composing images with areas of flat colour. Vignetting is the biggest optical issue facing the EF-S 15-85mm IS USM, although again it reduces greatly by f8 and can also be corrected effectively in software.

Before wrapping-up here, how does the EF-S 15-85mm IS USM compare to equivalent models for rival systems? When zoomed-in out and in, the Nikkor DX 16-85mm VR scored 59% and 78.2%, the Sony DT 16-80mm scored 53.4% and 71.8%, while the Olympus ZD 12-60mm scored 85.4% and 95.7%. So in terms of vignetting, the Canon performs the worst of this particular group.

That's enough for our formal tests now, so let's check out some more real-life sample images in our Canon EF-S 15-85mm IS USM Gallery.

Canon EF-S 15-85mm IS USM Vignetting / Light fall-off compared to other lenses

Canon EF-S 18-55mm f/3.5-5.6 vignetting wide / tele
 
Canon EF-S 17-85mm f/4-5.6 IS vignetting wide / tele
 
 
 
EF-S 18-55mm at 18mm f3.5
Mean corner fall-off: 68.8%
 
EF-S 18-55mm at 55mm f5.6
Mean corner fall-off: 83.8%
 
EF-S 17-85mm IS at 17mm f4
Mean corner fall-off: 57.8%
 
EF-S 17-85mm IS at 85mm f5.6
Mean corner fall-off: 77.5%


Canon EF-S 18-135mm f/3.5-5.6 IS vignetting wide / tele
 
Canon EF-S 18-200mm f/3.5-5.6 IS vignetting wide / tele
 
 
 
EF-S 18-135mm IS at 18mm f3.5
Mean corner fall-off: 53.2%
 
EF-S 18-135mm IS at 135mm f5.6
Mean corner fall-off: 63.8%
 
EF-S 18-200mm IS at 18mm f3.5
Mean corner fall-off: 37.7%
 
EF-S 18-200mm IS at 200mm f5.6
Mean corner fall-off: 41%


Canon EF-S 15-85mm IS USM results : Sharpness 15mm / Sharpness 50mm / Sharpness 85mm / Geometry / Vignetting


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