Ali Shah wrote:
> ........Sigma just
> announced new four-third mount lenses....god only
> knows when they will be released. Interesting to note
> that they each have an asterick saying that on a
> four-third mount camera - the focal length will
> double. The 24mm had me excited except when I read the
> * that says the lens will be a 48mm on Olympus bodies!
>
I think you are confusing two different things, focal length and field
of view.
Focal length is s simple characteristic of any lens, completely
unrelated to it's use. If you image a subject at infinity, it will be in
focus at a fixed distance from the nodal point in the lens (or rear
nodal, for complex lenses).
In an imaging system, the area of the subject captured depends on the
size of the sensor/film placed at the focal plane. Since the 4/3 sensor
is much smaller (about half the size) than a 35mm film frame, it doesn't
'see' as much of the subject as a larger sensor would with any
particular focal length lens.
So a 50 mm focal length is a mild tele on 4/3, normal on 35mm, wide
angle on 6x6 cm and ultra wide on 4x5' film.
When Sigma says they are selling a 24 mm lens, that's correct. Your
statement, "...that says the lens will be a 48mm on Olympus bodies!" is
not correct and probably not exactly what they said. A correct statement
would be "A 24 mm lens on 4/3 has a field or angle of view equivalent to
a 48 mm lens on 35 mm film."* People who have worked in multiple formats
have always been aware of these issues. Those who have always worked in
one format, often tend to equate fl with fov in their minds.
Still a bummer, I understand, but they can't advertise it as 48 mm for
the simple reason that it isn't.
Moose
* diagonal measure
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