Why do some RAW files show black corners at the wide end on compact zoom cameras?
Asked 9/14/2017
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I opened a sample RAW from a Sony RX10 IV in RawTherapee, and at the widest focal length the image shows solid black corners. This is more than normal vignetting, and it does not appear at longer focal lengths. If I manually apply lens distortion correction, the problem goes away.
What causes these black corners in RAW files? Does the lens fail to fully cover the sensor at the wide end, or is this related to automatic in-camera lens correction that would normally be applied to JPEGs? Is this common on compact cameras with built-in zoom lenses?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
8y ago
2 Answers
5
Yes, most likely the lens doesn't cover the whole sensor at the wide end - but correcting for barrel distortion (which happens automatically when shooting JPEG) moves the vignetted corners outside the corrected image area. It's a trick employed to shave just a tiny bit more off the size of the lens.
Originally by user14547. Source · Licensed CC BY-SA 4.0
user14547
8y ago
0
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The black corners are most likely from the lens at the wide end not quite covering the full corrected image area. On many compact zoom cameras, the lens has noticeable barrel distortion at the widest setting, and the camera normally fixes this automatically for JPEGs.
When that distortion correction is applied, the image is stretched/remapped, which pushes the dark vignetted corners outside the final frame. If your RAW software doesn’t yet know the camera’s lens profile, it shows the uncorrected RAW data instead, including those black corners.
So this is not the same as simply mounting the wrong lens on a camera body. It’s more a result of lens design plus digital correction. Manufacturers sometimes allow this because it helps keep the lens smaller and more compact.
Yes, this can be normal on compact cameras with built-in zooms, especially at the widest focal length.
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