Calculating 35mm focal length equivalent
- From: DigiSus <info digisus info>
- To: eog-list gnome org
- Subject: Calculating 35mm focal length equivalent
- Date: Mon, 21 Jul 2008 23:11:52 +0200
Thanks Felix for implementing variant B. :-)
As to calculation of the 35mm equivalent; it is not so bad/difficult. I
think the problem is rather to get the needed data (and it is not 14
Let me give a few points so you can think about what could make sense to
1) The "standard" format for images on a film role from the ancient
analog world is 24x36mm, having a diagonal of d_full=43.27mm.
2) Digital cameras have very differently sized CCD sensor chips, all of
them usually smaller than the full format.
3) To calculate the crop factor/focal length multiplierFLM (different
names, same thing), one needs the diagonal d_ccd of the actual CCD
4) Then, it is quite easy: FLM = d_full / d_ccd
5) With that the measured focal length (EXIF:FocalLength) times the MLF
gives the equivalent focal length in 35mm film camera.
I did not find the CCD size in the EXIF spec. Am I wrong?
If not, we simply take the info from the EXIF (if it is there),
calculate it and that's it.
If it is not there, we would need to look up the camera model/make
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