Using simple trig to calculate the angle of view half way between 100mm
and 200mm gives 133.2mm
Starting with the 50mm lens, halving and doubling its 42.2 deg angle of
view, then inserting angles of view half way between them gives the
following result. The first column is the calculated angle of view. The
second is the calculated focal length. the third is the focal lengths of
the original series of Zuikos, before the super teles.
Angle Focal Len.
Deg. Calc. Act.
168.8 18 18
126.6 20 21
24
84.4 27 28
63.3 34 35
42.2 50 50
31.7 66 85
21.1 98 100
15.8 131 135
10.6 196 200
7.9 261 300
5.3 391 400
4.0 521 600
2.6 782 1000
Remarkable agreement over the range of 18-200mm except for the insertion
of the 24mm and the slightly long 85mm. Halfway between 126.6 and 84.4
deg. is 105.5 deg, or a 23mm lens. I would guess the move up from
theoretical 66mm to 85mm is for the very non-mathematical purpose of
portraits of people.
My conclusion? 135mm isn't oddball at all, but part of a mathematical
sequence of angles of view!
Moose
AG Schnozz wrote:
I think this is a "modern math" thing. If multiplications are
supposed to be rough multiples of focal length then why is 135mm
the oddball? Hmm????
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