Canon 15- 85 Vignetting

Started Aug 27, 2010 | Discussions thread
Paul De Bra
Paul De Bra Forum Pro • Posts: 12,499
Canon is "cutting corners" here (really).

My 17-85IS was the same and even the expensive 17-55 occasionally shows a bit of this.

What is most likely going on is that the IS is moving the image circle slightly off-center. And because Canon has been cutting corners (matter of speech) on the glass, making the image circle too small to allow for the IS to go off-center, Canon is now cutting corners literally.

The vignetting correction in DPP will not fix this problem as it only fixes the designed light fall-off when the lens is centered, not when IS is moving it off-center.

If you experience the same asymmetrical vignetting when IS is turned off then it may be a problem with your copy of the lens. If it's only with IS on then it is just the result of the image circle being too small. My 17-85IS lens (sold years ago) showed similar asymmetric vignetting mostly around 26mm. The 15-85IS is designed differently, so the point where the image circle is cutting corners the most may be different as you seem to experience.

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