Hi,

I was just fiddling with lens correction on an image taken with my 
Pentax K5II and a Samyang 14mm/2.8 lens.

In the lens correction module it comes up with "Pentax K-5 II" for the 
camera, and "A Series Lens" for the lens, and applies no noticeable 
distortion corrections.

If I change the camera to another Pentax APS-C camera (or a Generic 
1.5x camera), suddenly it applies a pretty good pincushion correction.

How can this be, when darktable has apparently not identified my lens?

This lens does not communicate electronically with the camera. I told 
the camera the focal length was 15mm (as it has no 14mm option) and this 
is reflected in the exif data. Has darktable somehow just made a 
reasonable guess at how much pincushion a 15mm lens on APS-C will have 
??

I will make the effort to calibrate the lens and submit it to LensFun 
but I am just curious what's going on here and where darktable is 
getting its correction parameters from in this instance. I am using 
darktable 1.1+1175~g2434bf0.

Secondly it won't let me choose any other lens unless I select a camera 
other than the automatic "Pentax K-5 II".

Thanks in advance

Russell


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