Calculating 35mm focal length equivalent

[DigiSus <info digisus info>]

Hello

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 
parameters).

Let me give a few points so you can think about what could make sense to 
implement.

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 
sensor chip.

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.


Problems/Solutions:
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 
somewhere...


Regards,
Marcus