Op Tue, 20 Dec 2005 14:29:43 +0100 schreef Don Sanderson
<[EMAIL PROTECTED]>:
Maybe someone can enlighten me.
Some zoom lenses are physically longest at
their longest focal length, such as the FA24-90.
Others, like the FA28-70/4 AL are physically
shortest at their longest FL.
Hi Don,
My FA 28-70 is shortest at 50mm. It extends a tiny bit towards 70mm. How
does the FA 24-90 change exactly?
Does anyone know why this is, and what
advantage or disadvantage each design has?
I would guess short zooms generally use a design that goes from long to
short to long angain (usually longest at shortest focal length), and
telezooms just extend out (get longer as they get longer, if you know what
I mean). As telelenses tend to be less complex anyway, I would guess that
this is simply the easiest way to do a zoom if you can get away with it.
Wikipedia has a nice article <http://en.wikipedia.org/wiki/Zoom_lens> on
zoom lenses. It does not explain the observed length changes, so there is
obviously more involved. I could not find better articles on the matter.
If someone has links, I;d be interested.
--
Regards, Lucas
