08-14-2011, 06:04 PM
[quote name='dave9t5' timestamp='1312736815' post='10456']
The physical spec of this lens must be wider than 12mm. Ergo, the focal length (12mm) is not the focal length (<<12mm).
[/quote]
A strictly rectilinear corrected lens would have to be a bit wider than 12mm to
fulfill the observed behaviour (angle of view in the corrected image matches 12mm exactly).
But imagine, this lens is not a strictly corrected rectilinear lens ... this way, it can as well
have a focal length of 12mm and be a bit wider than a rectilinear 12mm lens is.
Like the Samyang 8mm (stereografic fisheye) has the same field of view than a 10mm
(equisolid) fisheye (both on crop-1.5/1.6).
Just a thought ... Rainer
The physical spec of this lens must be wider than 12mm. Ergo, the focal length (12mm) is not the focal length (<<12mm).
[/quote]
A strictly rectilinear corrected lens would have to be a bit wider than 12mm to
fulfill the observed behaviour (angle of view in the corrected image matches 12mm exactly).
But imagine, this lens is not a strictly corrected rectilinear lens ... this way, it can as well
have a focal length of 12mm and be a bit wider than a rectilinear 12mm lens is.
Like the Samyang 8mm (stereografic fisheye) has the same field of view than a 10mm
(equisolid) fisheye (both on crop-1.5/1.6).
Just a thought ... Rainer