Today's smaller, less expensive lenses rely a lot on digital corrections which, in the film and early digital days, were accomplished with the optical design of the lens. Smaller and less expensive being good things, my two current zoom lenses rely on digital corrections to varying extents.
The RF 16-28mm f/2.8 IS STM lens, at its widest end, relies massively on digital corrections. Here is what an uncorrected file looks like when you have software that lets you see it. In camera, and using Canon's Digital Photo Professional (DPP) software the corrections are forced and you never see this. Vignetting (peripheral illumination), distortion and cropping need to be applied
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| no vignetting, distortion or cropping corrections applied |
Here is a partially corrected file using DxO PhotoLab 8. Vignetting, distortion and cropping has been applied. The uncorrected file is around a 14mm field of view. This file is cropped manually to something a bit wider than 16mm.
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| vignetting, distortion and cropping corrections applied |
Before we get to the Canon DPP processed file, here is a PhotoLab finished file of the image above. Some vignetting in the lower corners remains, possibly because the crop is wider than 16mm and the sky is brighter than the water reflection. It's also possible that the wider cropping includes some shading from the lens hood.
And here is how Canon's DPP software automatically corrects the vignetting, distortion and cropping. It is reportedly a 16mm field of view which you'll notice is tighter than the image above.
The DPP software is not as flexible as the DxO software when it comes to lighting adjustments. DPP only has adjustments for shadows and highlights, for instance, while DxO has separate adjustments for blacks, shadows, midtones and highlights.
Finally, here is how I finished off the file yesterday in a 16:9 aspect ratio. This eliminates most of the lower vignetting but loses the moon reflection.
