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http://bugs.kde.org/show_bug.cgi?id=151685
------- Additional Comments From bug christianmayer de 2007-12-01 16:36 -------
> > Absolutly, we need formulas + context to use + full descriptions to add on API doc... else nothing will be done (:=)))
Here are some collected formulas for part one (more might come later...)
The information of this post comes from
http://www.dslr-forum.de/showthread.php?t=21047 (for those that can
understand German...).
Some definitions:
f: the real focal length in mm (the number on the lens;
independent of the sensor size)
f_equiv: the felt focal length when used on a crop camera by comparing
the picture angle
Y: the crop factor (Canon DSLRs have e.g. mostly 1.6)
s_[o,p]: size of the object (the thing infront of the camera) or the
picture (i.e. 1/2 of the sensor chip) in mm
d_[o,p]: distance of the object or the picture (i.e. sensor) to the
principal plane of the lens in mm
S: the size of the sensor in mm (and thus S = 2*s_p) - depending
on the context it might be length, height or diameter
S = [36mm x 24mm] / Y
V: reproduction scale, the ratio between picture size and object
size V := s_o / s_p
a°: picture angle (the real one, not the simplified one with the
object at infinity; changes with focus setting)
a°_inf: picture angle when d_o = infinity (that's the one usually used
in advertising material of the manufacturer)
I'm assuming that the EXIF will tell me: f, d_o, S
to calculate the rest here are some formulas:
class optics (just for background; not needed):
1/f = 1/d_o + 1/d_p
s_o/d_o = s_p/d_p
interesting for the digiKam user (thus the results should be shown in
this whish):
Y = [36mm x 24mm] / S
V = f/(d_o-f)
a° = 2 * arctan( S*(d_o-f)/(2*f*d_o) )
a°_inf = 2 * arctan( S / (2*f) )
(note to the reader: this shows us that focal length at a croped camera
= crop_factor * real focal length is *only* correct when the lens is
focused at infinity! Thus:)
f_equiv = f*Y / (1 - f/d_o + f*Y/d_o)
V is important for macro photos (that have about a 1:1 ratio). It should
be displayed differently, depending on its value:
if( V < 1 )
printf( "%f : 1", 1/V );
else
printf( "1 : %f", V );
> > We working on more important parts currently (Database improvements + XMP support + KDE4 port). So all help is very usefull.
I know. :)
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