Ken Hart wrote:
> "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?
It's not the camera but the lens design. Fixed (wide) aperture zoom
lenses for SLRs that don't get darker on the long end are probably not
available with more than 3x of range like a 70-200 f/2.8 or f/4 at 2.8x
or 17-35/2.8 at 2x. Some of the bulkier point & shoot cameras do alright
considering their large zoom range but smaller models are too size
conscious to maintain aperture at longer focal lengths.
> 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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