My Canon EF mount Tamron 20-40 always reports 21-39 in the EXIF. I have
no idea how that info is generated by the lens. I've always wondered if
Tamron simply fudged a little on the advertising or whether it's minor
inaccuracy in the mechanism. Doesn't matter. It's a great lens except
for it's susceptibility to flare if the sun is near the edge of the frame.
Chuck Norcutt
On 2/25/2016 3:58 PM, Moose wrote:
Back when Modern and Pop photo did lens testing, they checked actual FLs
for their samples. Modern's criterion for meeting spec. was ±5%. Their
lab measurements for the samples of two OM Zuikos they tested were:
Spec FL Var. AOV
Zuiko 18/3.5 18.76 4.2% 98.1
Zuiko 21/2 20.15 -4.0% 94.1
Anyone with those particular two lenses would have, in effect, faster
and slower versions of the same AOV. Someone else, who hit the other
ends of the range, might have 17 and 22 mm lenses.
--
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