"ChrisCoaster" <ckozicki@[EMAIL PROTECTED]
> wrote in message
news:1d80c7c0-736a-4b58-a9db-82fe5e46e832@[EMAIL PROTECTED]
>A few months ago I wandered into this great forum and launched a
> discussion about the not-so-manual aspects of the "manual" mode on
> some compact(non-SLR) digital cameras.
>
> My chief complaint was that when zooming, the iris(f-stop value) was
> automatically decreased when zooming(increasing focal length).
>
> It was stated here that that is in fact what happens when you increase
> focal length - you reduce light intake. Fair enough.
>
Not _exactly_ true, there are other considerations that get very
technical.
The longer the focal length, the more difficult it is to make a 'bright'
lens. I've got a pair of older Canon lenses, both 200mm. One is a f/4.5,
the
other f/5.6. The brighter one is substanially bigger, heavier, and more
expensive. OTOH, the dimmer one is more comfortable to have hanging around
my neck!
> But how difficult, and for that matter how costly, would it be for
> manufacturers to allow a setting that "freezes" f-value at the
> operator's choice when zooming.
>
I can't speak about the costs of research & developement, or the cost of
adding a cam, ball bearing, or linkage arm to a lens... Let's just say
that
zoom lenses are tricky. There are lens elements moving to focus, and other
lens elements moving to zoom. Additionally, when you change zoom setting,
the focus may ****ft, so the movements of the zoom and focus elements have
to
be linked. In order to keep the cost down, something has to be cut, and
the
brightness of the lens is probably the best place to start, as that can be
made up with film speed or shutter speed.
> That is, keep f=2.0 or 3.0 or whatever while zooming out to, say, 4x
> or 6x optical, to really narrow the field of focus on the subject.
> That's what the really expensive manual SLRs allow one to do, right?
>
Of course you can have the features you want if you are willing to pay for
it. But your last sentence sums it up-- "really expensive". Actually, if
you
are looking at a 35mm SLR, there are a lot of them on the used market that
have fantastic features and a multitude of glass available at really
attractive prices. Because I use a 40 year old camera, I have a pile of
lenses to pick from, and a vast selection of camera bodies. The price that
I
paid over the years for this gear might, maybe, on a good day, get me a
top
of line dSLR with a standard lens. Of course, I'm not willing to drop down
from film quality to digital...
(BTW: the f/stop is a ratio, with "f" representing focal length. The
proper
way to write an f/stop is as a ratio, ie: "f / 22", the diagonal line
representing "divided by")
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