David,
I haven't a clue, but did make a coincidental observation this weekend. I
have a 50-250 f/5. While shooting a soccer game, I noticed that the
shutterspeed my OM-4T chose at 250 was almost a full stop different then the
shutter speed chosen at 50.
Seems to me like it IS a variable aperture. Does this mean it's truly f/5
at 50 or 250. I'd suspect 50 and more like f/8 at 250. One of these days
I'll mount a prime on the body and compare results.
Tom
From: "David Jenkinson" <jenkinson@xxxxxxxxxxxxxxxxxxxxxx>
> Dear all
> I've been wrestling with a bit of a riddle ever since I read something on
> one of the photo newsgroups, and try as I might I can't figure it out in
my
> head.
> Somebody was asked which kind of zoom lens is better: fixed or variable
> aperture?
> The answer is easy for me. Using as I do a manual camera, a fixed
aperture
> lens is certainly more convenient as it saves you having to adjust
exposure
> after zooming (aside from if the light had changed etc.) if you're
shooting
> wide open.
> But, and here's the rub.....as one of the answers pointed out,*all* zoom
> lenses, by definition *should* be variable aperture, shouldn't they?
After
> all, the focal length changes without the physical size of the opening by
> which light leaves the lens altering one way or the other. At least, it
> doesn't seem to on my 65-200/4. Bafflingly, the 35-70/3.5-4.5 I used to
> have did change size, as the aperture was stopped down a tad at the 70mm
> end. (If you've got one, try it.) To me this means that any lens with a
> fixed aperture must be a compromised design in some way, and also why
isn't
> my 65-200/4 a 65-200/2.8-4 or something like that. The only thing I could
> think of was that the lens is actually a 65-200/3.7674757 - 4.3323343, and
> for simplicity's sake it gets corrupted to 4. I've been kept awake
trying
> to figure this one out. Can somebody explain this to me in non baffling
> terms?
> Cheers
> Dave
>
>
> < This message was delivered via the Olympus Mailing List >
> < For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
> < Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
>
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|