Originally posted by shemazar Theoretically, there's a big difference in the FoV from 10mm and 12mm, but when looking at the specs between the two lenses, the Angle of View (not to be confused with FoV - field of view). The angle of view between them is only 3.4 degrees by spec sheets.
That's very odd. Theoretically (using trigonometry, not linear scaling), the difference in AOV should ~10 degrees.
The
102.4 - 63.8 specified for the Sigma 10-20mm F3.5 are very close to my theoretical values (~ 100.4 - 62).
However 12-24mm should result in ~90 - 53 degrees, not in the
122 - 84.1 degrees specified for the Sigma 12-24mm F4.5-5.6 or the
99 - 61 degrees for the Pentax DA 12-24mm F4.0.
The fact the the two 12-24 lenses are specified with rather different AOV is further evidence to something being a bit odd.
I would expect the Sigma's 10mm to give a considerably wider view then the Pentax' 12mm, not just a mere 3.4 degrees.
BTW, I calculated the angle being formed by the wide (horizontal) dimension of the image only (which is consistent with the wikipedia definition of AOV). Perhaps others use a different basis.