Simple enough, it's the physical and material limitations of practical
lens design. Although there is a reasonably close relationship between
the focal ratio (ratio of effective aperture to focal length) to the
ratio of front element size to focal length from about 40-50mm up, the
wider angle the lens, the less connection there is. With advances in
glass formulation and optical design, this has improved. For example, my
old late '70s Vivitar 28mm/2.5 has a 46mm dia. front element while a
later Tamron design has a 23mm FE, just half the size. The faster Zuiko
28/2 has a 32mm clear aperture FE. Oly settled on a few standard filter
sizes to make life easier and cheaper for us, so if a design couldn't be
squeezed into 49mm, it went to the next standard size, 55mm. Having as
many as lenses as possible use the 49mm filter size vs. the 52mm of
Nikon was a point of pride and a selling point that emphasized how
compact their lens line was. All their original prime lenses from 21/3.5
to 200/5 used that size. With the introduction of the F2.0 series, the
early zooms and the faster teles, they had to go to 55mm. The really big
lenses use 72 and 100mm. The odd lens out is the late design 35-80/2.8
at 62mm.
Moose
Pete Prunskunas wrote:
The 35mm f2.0, 24mm f2.0, and 21mm f2.0 lenses are all 55mm
in diameter, while the 28mm f2.0 is only 49mm in diameter. This
is inconsistent. You'd think Olympus would have made them all
the same diameter in f2.0. Does anyone know the story behind it?
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