I’ve been puzzling over this for a while but now I think I know the answer. This is how Capture One (and DxO too, by the way), can appear to ‘see’ a wider angle of view than the camera can. It’s a particular characteristic of wide-angle lens corrections that looks like it shouldn’t even be possible but has a rational and extremely interesting explanation.
This particular photo was taken with a Canon RF 15-30mm F4.5-6.3 IS STM ultra-wide zoom, set to its minimum 15mm focal length. Like just about all modern mirrorless lenses, this one uses a hefty dose of digital correction to eliminate barrel distortion. In the old days, lens makers would do this optically because digital corrections didn’t exist, but today lens makers get an easy ride – or at least they can stop trying to correct distortion optically and concentrate on other aspects of image quality.
Read more
- Lens aberrations and what you can do about them
- More articles about lens corrections
- More articles about Capture One
So what happens is that if you shoot JPEGs with the camera the distortion correction is applied automatically and baked into the processed JPEG. If you shoot RAW, however, you have to rely on your RAW software having a correction profile for this lens (unlike other makers, Canon does not embed manufacturer lens correction profiles in its RAW files.)
Now if you open an ultra wide shot like this in Lightroom, Lightroom automatically applies a matching lens correction profile and the distortion is removed. But what the camera and Lightroom are doing is not quite the whole picture – very literally.
If you examine the same RAW file in Capture One you will very quickly notice a difference. Capture One has honoured the original camera crop with its own crop setting, but outside of this is a larger scene with a wider angle of view than the camera shows.
How is this even possible? It’s all because of the way barrel distortion is corrected…
Barrel distortion is fixed essentially by pushing the corners of the image outwards. Normally, in the camera (and Lightroom), these areas pushed outside the original crop are simply lost. But that’s not what Capture One does.
Instead, Capture One retains this extra image area and makes it available to you if you want to extend the original crop area. Sometimes the extra image detail at the edges is perfectly good and usable, sometimes it’s a little soft or may have excessive shading right in the corners. It depends on the lens.
Let’s see how this works.
Step 01: Check to see that Capture One has found a matching lens profile
Take a look in the Shape panel. If you see the lens name here, that means Capture One has a correction profile for this lens. Sure enough, it’s corrected the barrel distortion in this shot and the image crop matches what the camera shows after correction. But there’s something else. You’ll see in the Viewer that the cropped image doesn’t quite fill the window. There’s more outside the current crop area.
Step 02: Use the Crop tool
You can use the Crop tool’s drop-down aspect ratio menu to choose Original if you want to preserve the original aspect ratio (3:2 in this case) but I’m choosing Unconstrained because the correction process sometimes pushes the image width a little further than the height and I want to recover as much as possible.
Step 03: Expand the crop
The Canon RF 15-30mm is an especially interesting lens because the extra image area that can be recovered and used is substantial. It’s as if it’s going from a 15mm angle of view to 13-14mm. Look how much ‘wider’ this image is that before. Better still, the quality at the edges stays pretty good and is quite usable.
Step 04: Check the before-and-after versions
This comparison shows just how much more of the image area has been recovered in the expanded crop (below) compared to the original crop (top).
You get the same results with other digitally-corrected wide-angle lenses. The Canon RF 16mm F2.8 yields a similarly substantial increase in image area in Capture One. Not all lenses respond well, though. The remarkable Canon RF 10-20mm F4L IS STM can go even wider after correction in Capture One, but the extreme corners go dark, so there’s a limit to how far you can extend the crop.
DxO PhotoLab and PureRAW offer the same capability. They too retain the full image area after distortion correction and can offer a wider angle of view than that captured by the camera. Just to re-iterate, the camera is doing the same kind of correction but is not retaining the expanded image area outside the original crop.
If you use DxO PureRAW to batch process your RAW files into part-processed Linear DNGs, you’ll see that among the processing options there is one for cropping, and the key setting here is Maximum Rectangle. If you select his, PureRAW will crop to the maximum possible image area, which is typically wider than the camera’s native crop.
There is something extra special in discovering that your favourite wide-angle lens is even wider than you thought in Capture One. It’s not ‘seeing’ a wider angle of view through the same lens, of course, because that would be impossible, but what it is doing is preserving a larger image area after correction that other programs (and the camera) will discard.
