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From: seifert@hammer.UUCP (Snoopy)
Newsgroups: net.rec.photo
Subject: Re: Zoom lens comparisons
Message-ID: <1713@hammer.UUCP>
Date: Thu, 19-Dec-85 12:27:05 EST
Article-I.D.: hammer.1713
Posted: Thu Dec 19 12:27:05 1985
Date-Received: Sat, 21-Dec-85 05:28:07 EST
References: <632@wjvax.wjvax.UUCP> <11900005@uicsl>
Reply-To: tekecs!doghouse.TEK!snoopy
Organization: The Daisy Hill Puppy Farm
Lines: 17
Summary: 

In article <11900005@uicsl> mather@uicsl.UUCP writes:

>I bought the Vivitar Series I 28-90 f2.8-3.5  and the lens does NOT stay
>in focus as you zoom. This is typical of fast zooms, but I find it a pain
>compared to my Vivitar Series I 70-210 f2.8-4.0 which I can focus at the
>farthest focal length (210) and then zoom back for optical framing.

Sounds like the 28-90 is NOT a zoom lens.  A zoom lens does stay in
focus throughout the focal length range.  This is essential for
motion picture cameras, and for some still applications.  Not everyone
requires a true zoom, so they make non-zoom variable focal length lenses,
which can then be lighter, smaller or cheaper, since they have one
less design constraint.   I think there's a special term like
"veri-focal" for them.

Snoopy
tektronix!tekecs!doghouse.TEK!snoopy