Since Adobe released the lens profiles for the Batis lenses, it's been possible to open and correct Batis RAW files in ACR. I decided to use one of the RAW files Guy was kind enough to supply here. (Thank you, Guy.) It is an interesting file, because it is blazingly sharp, even though it was shot wide open, at f1.8. It is full of fine detail. So, it presents us with a good way of seeing what happens to resolution when distortion is corrected.
Click on images if you like to see them larger. The differences are small.
First, from an uncorrected TIFF, using my typical initial settings, at 200 percent:
Next, with the distortion profile applied, same settings otherwise:
Then, no distortion correction, but a horizontal level correction:
Next, with both distortion and level correction:
Finally, with distortion and level correction, plus increased deconvolution sharpening:
I'm not sure if the differences will be visible to you in these jpegs, but they are definitely visible in the TIFFs. I would summarize them this way:
1. Applying distortion correction visibly decreases sharpness at 200 percent. (At 100 percent, it is hard to see, but slightly visible.)
2. Applying horizontal level correction decreases sharpness also, possibly a bit more than distortion correction.
3. Applying both horizontal level and distortion correction isn't noticeably worse than doing just one of those corrections. Resampling is resampling, for the most part.
4. Applying both corrections, then moderately increasing deconvolution sharpening, restores most of the sharpness.
I almost always do some kind of horizontal level correction. For the purpose of printing, I usually preview my files at 50% or 66%, not 200%. One other thing: the original file is full of moire. To knock that down, I might shoot at around f11, which would cause some diffraction. This could be partly reversed with good sharpening technique.
Others have predicted these results, and made similar tests. I wanted to check this lens in particular, and see how things might come out with my work flow.