Why doesn’t UFRaw automatically match a lensfun profile for my Canon EF-S 18-135mm lens?
Asked 6/22/2018
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2 answers
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In UFRaw, some RAW files from my Canon EOS 600D correctly auto-detect the lens profile from lensfun, but others do not.
For example, my EF-S 17-85mm is matched automatically because the EXIF lens name corresponds to a lensfun entry.
But with my Canon EF-S 18-135mm f/3.5-5.6 IS USM, the EXIF shows:
- Lens Model: EF-S18-135mm f/3.5-5.6 IS USM
- Lens Type: (36912)
And lensfun has a matching model entry:
- Canon EF-S 18-135mm f/3.5-5.6 IS USM
Why would UFRaw fail to auto-detect this lens even though a lensfun profile exists? Is it related to EXIF lens-name mapping, lensfun’s database rules, or the camera/lens crop-factor differences?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
8y ago
2 Answers
2
The lens type in Exif may not be mapped to a usable lens name by the software you're using. In the case of darktable, this depends on exiv2, which may not have this lens mapping if it's an older version of exiv2. To compound the problem, exiv2 may not continue to provide this functionality in the future, so even recent versions may exhibit this problem for recent lenses. The suggested solution is for users to provide their own mappings for the lenses they use.
Not a factor in this case, but as general information: Lensfun normally won't use a profile created using a camera with a smaller sensor for an image created using a camera with a larger sensor. This is because, while an adjustment in the opposite direction can be accurately calculated, this case would require assumptions about what the lens does in the areas near the edges that weren't part of the original profile.
Originally by user37649. Source · Licensed CC BY-SA 4.0
user37649
8y ago
0
Generated from our catalog & community — verify before relying on it.
Most likely the problem is not the lensfun profile itself, but the EXIF-to-lens-name mapping used before lensfun can match it.
For some lenses, the software can translate the EXIF lens data into a usable lens name; for others, it may only see a numeric lens type code like “36912.” If that code is not mapped by the metadata library your software relies on, automatic matching fails even though lensfun already contains the correct lens profile.
This can depend on the version and capabilities of the EXIF library used by the RAW converter. Older versions may not know newer lens IDs, and in some software stacks this mapping is incomplete.
The crop-factor differences you listed are probably not the cause here. A general lensfun limitation is that it normally won’t apply a profile made on a smaller sensor to images from a larger sensor, but that is a separate issue and not the likely reason in this case.
In short: UFRaw probably isn’t converting that lens’s EXIF data into the exact lens name lensfun needs. A manual mapping or updated metadata support is the usual fix.
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AI8y ago
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