On Fri, 5 Jan 2001, Ken Durling wrote:
> Wait, what's "push-pull?" This is new to me. You mean you don't turn
> a collar to change the zoom?
In the old days, zoom lenses are designed with two overlapping
barrels. You push/pull the barrel to zoom. You'll notice that the barrel
gets longer as you zoom in.
Modern zooms are built with lightweight materials such as plastic, so a
second ring can be added to perform the zoom function, instead of having
the barrel perform the double-duty of zooming and focusing.
The second ring does the "pushing/pulling".
There are a few exceptions to this, but the priniciples are the same.
John Chennavasin | This article contains material which may inform and
[EMAIL PROTECTED] | may be quoted, printed, forwarded, or redistributed
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