[LRflex] Re: aperture - zoom - puzzles me
- From: Bob Shaw <rsphotoimages@xxxxxxxxxxx>
- To: leicareflex@xxxxxxxxxxxxx
- Date: Mon, 6 Nov 2006 22:34:49 -0800
I can tell you that my R8 and 9 will display different apertures for
the R 28-90 as it goes from 28 (2.8) out to 90mm (4.0).
Same for the 70-180 APO except that it is capable of constant 2.8.
Hope this helps a little bit.
Bob in Seattle
On Nov 6, 2006, at 18:23, Douglas Herr wrote:
On Nov 6, 2006, at 12:37 PM, Philippe Amard wrote:
> Hi list,
>
> I never thought of this with the R3 and 4 as I knew they were more
> mechanics than elcectronics.
> BUT
> I recently bought an R8 and have kept wondering about the aprerture
> displays I get in the viewfinder.
> When I use one of my zoom lenses, the values are not altered in any way
> by the focal length I'm using - I mean, zooming in or out does not
> affect either the speed or the stops shown in the finder (provided that
> the background is uniformly lit of course).
Some zooms - formerly most zooms - are designed to compensate for the
changing focal length with a changing entrance pupil. Those known as
constant-aperture zooms are the same aperture at each marked setting
regardless of the focal length. When lens designers allowed the
freedom of a variable aperture vs. focal length, they can optimize for
other parameters, most notably size and weight. Among modern zoom
lenses you will see that pro-level zooms are more often than not a
constant-aperture design while consumer-grade zooms are almost always
variable-aperture designs. However one must not assume that a
constant-aperture zoom is nessesarily a pro-grade lens or that a
variable-aperture lens is consumer junk.
Doug Herr
Birdman of Sacramento
http://www.wildlightphoto.com
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