Dear users of Tamron lenses for Canon EOS cameras.
Thank you for using our Tamron lenses.
When using a Tamron lens in combination with a Canon EOS 77D, 800D, 1D X Mark II or 5D Mark IV camera, we recommend that you switch the camera menu function "Lens Abstraction Correction" OFF in the camera menu before taking pictures. This prevents strange and unnatural-looking over-corrections resulting in purple/green color borders and artificial gray markings on the corners.
However, you can only disable the function permanently in the "manual" modes:
Program mode, shutter speed priority, aperture priority, and full manual mode.
If one of the scene modes, such as portrait, landscape, sports, etc., is selected, the "Lens Abstraction Correction" will always be set to ON, causing strange discoloration in the picture.
This is NOT a malfunction of the Tamron lens, but an incorrect and excessive operation of the correction function in the Canon cameras. This effect may even occur with some canon lenses or other brands.
For correction of the "natural" and minimal aberration of a Tamron lens:
Tamron has made profiles available for Adobe Photoshop and Lightroom lens correction and anyone who photographs in raw can enable this lens correction and automatically correct not only aberration, but also vignetting and distortion. DXO Optics Pro and DXO Photolab software have also built in this lens correction for hundreds of camera+ lens combinations.
Every megazoom, regardless of brand, suffers slightly more from chromatic aberration than a short zoom with the same wide-angle position. The best solution to reduce aberration and vignetting is to use an aperture. The best result with a megazoom is achieved with an aperture of F8-F11.