RE: Variable zoom question - FA28-70/4

[Kent Gittings]

That is why constant aperture zooms generally cost more than variable ones.
Kent Gittings

-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]]On Behalf Of Christopher Lillja
Sent: Thursday, December 06, 2001 2:52 PM
To: [EMAIL PROTECTED]
Subject: RE: Variable zoom question - FA28-70/4


This whole thing seems to hinge on using the term aperture and F
interchangeably. I don't believe they are. F is commonly used to denote
relative aperture. And some folks seem to be using aperture to refer to
absolute aperture. What a huge urination contest over some sloppy
language

Not to pick on Kent but, incidentally, in regards to his comment:

First off what you say could be done however making the
diaphragm change with focal length is the hard way to do it. In fact I don't
know of a single lens designer who could make that work very well because
most zooms don't have much in the way of zoom/aperture direct interaction.


My FA 28-70/4 does exactly that and it does it very, very well. Great little
lens. Since the lens mechanically varies the absolute aperture in proportion
to focal length setting, relative aperture F is maintained - even when it
is used on my K1000, ME, or MZ5. On my other zooms, the mechanical F
scale/setting only indicates the correct relative aperture at the widest
setting.

Chris Lillja
School Publications Guy
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RE: Variable zoom question - FA28-70/4

[Christopher Lillja]

This whole thing seems to hinge on using the term aperture and F interchangeably. I 
don't believe they are. F is commonly used to denote relative aperture. And some 
folks seem to be using aperture to refer to absolute aperture. What a huge urination 
contest over some sloppy language

Not to pick on Kent but, incidentally, in regards to his comment:

First off what you say could be done however making the
diaphragm change with focal length is the hard way to do it. In fact I don't
know of a single lens designer who could make that work very well because
most zooms don't have much in the way of zoom/aperture direct interaction.


My FA 28-70/4 does exactly that and it does it very, very well. Great little lens. 
Since the lens mechanically varies the absolute aperture in proportion to focal length 
setting, relative aperture F is maintained - even when it is used on my K1000, ME, 
or MZ5. On my other zooms, the mechanical F scale/setting only indicates the correct 
relative aperture at the widest setting.

Chris Lillja
School Publications Guy
-
This message is from the Pentax-Discuss Mail List.  To unsubscribe,
go to http://www.pdml.net and follow the directions. Don't forget to
visit the Pentax Users' Gallery at http://pug.komkon.org .