Created attachment 100831 [details]
Screenshot digikam with selected image from my panasonic camera showing the 35mm focal length info

Hi,

i'm using a self written tool to analyze my pictures based on the info in the digikam4.db file to 
get the most used aperture, focal lengths, day with the most pictures taken etc.

In mid 2014 i changed my main camera from a Panasonic G5 to a Olympus OM-D E-M10.
The new Olympus camera don't fill the the exif field "FocalLengthIn35mmFilm" like my Panasonic camera before.

Example:
jhead -v benjamin-_2016.08.18_20-03-58_2490.JPG | grep 'Focal\|model\|make' 
        FocalLength = 20/1
Camera make  : OLYMPUS IMAGING CORP.  
Camera model : E-M10           
Focal length : 20.0mm

jhead -v mulata_2014.07.06_14-27-02_0807.JPG | grep 'Focal\|model\|make'
        FocalLength = 450/10
        FocalLengthIn35mmFilm = 93
Camera make  : Panasonic
Camera model : DMC-G5
Focal length : 45.0mm  (35mm equivalent: 93mm)

After importing the pictures, the field "focalLength35" in the digikam database has no value for the pictures from the olympus camera.

I  noticed, that the 35mm info is also missing in the exif info tab. See screenshots.

it's hard to compare images from cameras with different seized sensors without the 35mm focal length as common base.

The tool "exiftool" calculates the missing info  (i think throug other information stored in the exifs like e.g. sensor dimension in mm):

exiftool *2490* | grep 'Focal\|Make\|Model'
Make                            : OLYMPUS IMAGING CORP.
Camera Model Name               : E-M10
Focal Length                    : 20.0 mm
Focal Plane Diagonal            : 21.6 mm
Focal Length                    : 20.0 mm (35 mm equivalent: 40.1 mm)

I think digikam should also calculate the missing focal length, if possible, on import.
It is not possible to calculate it only with the informations stored in the database.