08-07-2011, 07:45 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]
No, it does not have to be SHORTER than 12mm.
It is not much corrected, and as is well known, uncorrected lenses are "wider" than corrected lenses.
Example.
Canon EF 15mm f2.8 fisheye (uncorrected lens). Angle of view (horizontal): 141°54'.
Canon EF 14mm f2.8 L USM (corrected lens). Angle of view (horizontal): 104°.
Ergo, of course it is wider when not corrected. Just the rules of the optical game. 12mm is 12mm, but field of view depends on level of correction.
The physical spec of this lens must be wider than 12mm. Ergo, the focal length (12mm) is not the focal length (<<12mm).
[/quote]
No, it does not have to be SHORTER than 12mm.
It is not much corrected, and as is well known, uncorrected lenses are "wider" than corrected lenses.
Example.
Canon EF 15mm f2.8 fisheye (uncorrected lens). Angle of view (horizontal): 141°54'.
Canon EF 14mm f2.8 L USM (corrected lens). Angle of view (horizontal): 104°.
Ergo, of course it is wider when not corrected. Just the rules of the optical game. 12mm is 12mm, but field of view depends on level of correction.