In a message dated 12/5/01 8:53:28 AM Eastern Standard Time, 
[EMAIL PROTECTED] writes:

> Subj:Re: Variable aperture zoom question
>  
> (Hi,
> 
> Fred wrote:
> > 
> > Mike:
> > 
> > > Suppose I have a variable aperture zoom lens, say 28-80mm
> > > f3.5-f5.6 If I set the zoom at 28mm, and set the aperture wide
> > > open, it should be f3.5. If I then zoom to 80mm, the effective
> > > aperture goes down to f5.6, right? And if I zoom to 50mm, the
> > > aperture will be somewhere in between, say f4 maybe.
> > 
> > Right.
> 
> Right.
> 
> > > Now suppose I set my zoom to 50mm @ f8.
> 
> That's not an easy task.  The aperture markings usually correspond to
> the widest aperture.  So, if you set the focal length to 50 and the
> perture ring to where "8" is marked, you will have f/8 @ 28 and
> something like f/13.5 @ 80 mm.
> 
> > > If I zoom out to 28mm, will the effective aperture stay at f8?
> > > If I zoom in to 80mm, will the effective aperture stay at f8?
> 
> > Nope, in both cases (although my understanding is that the relative 
> differences in aperture at different focal lengths diminish as one moves 
> away from "wide open").
> 
> If you did manage to set exactly f/8 @ 50 mm, the answer is no to both
> questions.
> 
> > In any event, if you're using TTL metering (which most of us use most of 
> the time), then the exposure recommendation should automatically compensate 
> for the variable aperture problem.
> 
> This is, fo course, correct and the most important thing.  The trouble
> with the variable apertures comes in play when you use manual flash,
> studio flash, etc.)
> 
> Cheers,
> Boz
_____________________________________________________
Pardon me if I misunderstand the gist of you response:
the operative question asked by Mike was : "if I set"...

Are you (anyone) now suggesting that setting the aperture manually, somehow 
changes the aperture as you zoom? 
How?
***Taking the aperture ring off "A" makes it a ~manual~ lens, or are you 
(anyone) saying that somehow, the camera/lens changes what is a (preset) 
aperture anyway? 
How?
 
Mafud
[EMAIL PROTECTED]
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