Max Apperture and Max. Shutter Speed Confusion-HELP

[bhaskar]

Hi,
Many zoom lenses have a specification like
f/2.8-4.0
What does the range mean ?
I know that one is max. aperture at wide angle end and
another at tele end. But why do zoom lenses have two diff
values ?
Also when you say max. aperture is say e.g. f/2.8
Does is mean that aperture can be opened max up to f/2.8
i.e. f/22 to f/2.8 or that it can be closed only up f/2.8
i.e f/2.0 to f/2.8 ?

Also when max. shutter speed for a perticular lens/apperture is 1/1000 of a sec .
Does it mean the shutter can't close any faster than 1/1000 of a sec or it
can't close any slower than 1/1000th of a sec ?

Many books are sometimes confusing on these terminologies, so i was hoping
some pro can clear this up for me.
thanks
bhaskar

[Godfrey DiGiorgi]

For focal plane shutter/interchangeable lens cameras, your statement is
nearly correct in all cases.

However, many cameras (film or digital) with leaf shutters site the
shutter in the lens coupled with or even implemented as a part of the
aperture mechanism. There are some limitations in some designs which
limit the available shutter speed range at particular apertures because
of this ... For instance, the top shutter speed may require an aperture
of f/5.6 or smaller in many cases.

Godfrey

In article <bf1m48$j2s$1@sparta.btinternet.com>, Martin Francis
<Mcsalty@btinternet.com> wrote:

> > Also when max. shutter speed for a perticular lens/apperture is 1/1000 of
> > a sec .
> > Does it mean the shutter can't close any faster than 1/1000 of a sec or it
> > can't close any slower than 1/1000th of a sec ?

>
> The shutter is in the body, not the lens. The body controls the shutter
> speeds.

[Matti Vuori]

Jim Townsend <not@real.address> wrote in
news:vh8pr02j4bu2df@news.supernews.com:

> If your'e wondering if you can you make a lens that varies the focal
> length *and* aperture at the same time to keep everything constant..
> (ie 28-125mm f/2.8).. Yes.. You can. There are such lenses, but
> they are EXPENSIVE.. So the common people have to put up with zoom
> lenses with varying 'f' ratings :-)

No, they don't. They can just buy an Olympus C-4000.

--
Matti Vuori, <http://sivut.koti.soon.fi/mvuori/index-e.htm>

[Werner Spreeuwenberg]

When the lens is zoomed in and the aperture is set to its maximum, the
camera lens will let through less light than when the lens is set to
wide-angle as the light will have to travel a longer distance from the
camera's lens to the film. As the aperture indicates the amount of light
that is passed to the lens it is also true that the value of the aperture
will differ when using different zoom values. The actual opening of the
aperture ring will stay the same, but the value differs.

The amount of light passed to the film affects the depth of the photo. To
get a larger range into focus you'll use a higher f-value while a lower
f-value will result in a smaller part of the picture (in front and behind of
your object) being in focus.

The shutter speed either freezes the object or let you add movement to your
photo by using a slower shutter speed.

How to use this:
1. Set the film's ISO value ( or ISO indicator when using a digital camera)
to the desired setting. ISO 100 for daylight conditions to ISO 1600 for near
pich dark conditions)
2. Leave the camera on auto and let the camera focus and decide the
approppriate apperture and shutter speed. Keep the zoom on the zoom you'll
want to use when making the photo.
3. Every f/stop indicates a doubling of the amount of light that is passed
through. If you want to double the shutter speed from lets say 1/250 to
1/500 you'll also have to double the amount of light, f/8 should then be set
to f/5.6

Also remember that a teleconverter will also convert the aperture because
the light will have to travel further. With a 2x converter a f/4 will result
in a f/8.

Sorry Martin, but you'll have to read more up to date books before awaiting
a fee. There is ample digital camera's on the market with more modes than P
(even SLR digital camera's are out).
Wide angle lenses does not neccesarily mean a faster lens. The maximum
aperture (value determined by the parts used inside the lens) determines the
speed of the lens. A 18mm f/2 is faster than a 18mm f/4.0.
It is also not cheaper to make a lens with a 'fixed maximum aperture' as the
opening of the aperture will allways stay the same, the amount of light and
thus also the value of the aperture differs with different zoom values.

Werner Spreeuwenberg

"Martin Francis" <Mcsalty@btinternet.com> schreef in bericht
news:bf1m48$j2s$1@sparta.btinternet.com...

> "bhaskar" <vkbhaskar@yahoo.com> wrote in message
> news:a9a6db62.0307151132.2e21998c@posting.google.c om...

> > Hi,
> > Many zoom lenses have a specification like
> > f/2.8-4.0
> > What does the range mean ?
> > I know that one is max. aperture at wide angle end and
> > another at tele end. But why do zoom lenses have two diff
> > values ?
> > Also when you say max. aperture is say e.g. f/2.8
> > Does is mean that aperture can be opened max up to f/2.8
> > i.e. f/22 to f/2.8 or that it can be closed only up f/2.8
> > i.e f/2.0 to f/2.8 ?

>
> Zoom lenses change aperture as you zoom for optical reasons; I could

explain

> further, only it's probably unneccessary (and i'd doubtless get it wrong
> anyway). From my own understanding, it is cheaper to make a lens with an
> inconsistent max aperture than one which maintains a constant max

aperture.

> The resulting non-constant-max-aperture lens is also smaller and lighter.
>
> The aperture scale goes in stops: f1.4, f2.0, 2.8, 4, 5.6, 8, 11, 16, 22,
> 32. Anything between these numbers is a fractional stop. A stop is the

mark

> at which the amount of light reaching the film/sensor is halved from the
> previous stop, or double the next stop. so f2.0 allows twice the light as
> f2.8. The more light allowed onto the film/sensor, the faster shutter

speed

> can be used. This is why wide aperture lenses are called "fast" lenses.
>

> > Also when max. shutter speed for a perticular lens/apperture is 1/1000

of

> a sec .

> > Does it mean the shutter can't close any faster than 1/1000 of a sec or

it

> > can't close any slower than 1/1000th of a sec ?

>
> The shutter is in the body, not the lens. The body controls the shutter
> speeds. When in M mode, you change aperture and shutter speed controls

until

> the meter needle is roughly centred (in high contrast and backlit

situations

> it gets more complicated). In Av or A mode, the aperture is user-selected
> and the shutter speed is camera-selected in the same way you would select

it

> by hand, only it does it faster (and with modern cameras to a tighter
> tolerance, i.e. 1/3rd stops) than you could. Same goes for Tv or S mode,
> only vice versa. Set the aperture to a narrower value, and your shutter

will

> need to be open for longer (ie a longer shutter speed). For example, if a
> given scene is 1/125th at f8, at 1/250th the aperture will have to be set

at

> f5.6, else the scene will be a stop darker.
>
> I've never used P mode- no camera i've ever owned even had one- so I

haven't

> a clue about the specifics, except it chooses aperture and shutter speed

for

> you.

> >
> > Many books are sometimes confusing on these terminologies

>
> I think you're reading the wrong books...
>

> > so i was hoping
> > some pro can clear this up for me.

>
> ... and I think you give pros too much credit :-)
>
> All the above information can be gleaned from a Michael Langford or John
> Hedgecoe book about 35mm photography, and can mostly be applied to digital
> photography. The only exceptions are digital cameras that have only P

modes,

> and the fact that if an exposure is bad, it can be deleted and re-shot on

a

> digital camera (thus avoiding bracketing; whereby the same scene is shot
> several times at slightly different exposures)
>
> Hope to help. I await my fee (I accept cheques).
>
> --
> Martin
> [url]http://www.btinternet.com/~mcsalty[/url]
>
>

[Martin Francis]

> Sorry Martin, but you'll have to read more up to date books before
awaiting

> a fee. There is ample digital camera's on the market with more modes than

P

> (even SLR digital camera's are out).

Thanks for the heads up, but I sold a Fuji S2 on Saturday; doesn't mean the
OP has one. In fact, the OP really didn't state much about his/her own
camera, or even if he/she had one. There are still a number or low-end
compacts that don't have an option to go into full-manual exposure control.
Big sellers like the Optio S, Ixus II and Dimage XT all lack A and S modes,
and I applaud Canon for releasing budget compacts that have this option
clearly advertised on a top dial. It's a big selling point with the 10D
buyers who realise they can't carry their LUSMIS everywhere, but still want
to buy Canon.

--
Martin
[url]http://www.btinternet.com/~mcsalty[/url]

[STIG]

> Also remember that a teleconverter will also convert the aperture because

> the light will have to travel further. With a 2x converter a f/4 will

result

> in a f/8.

This is true for film converters but is it true for converters designed for
digital cameras? On my Nikon c4500 with the 2x teleconverter installed I
notice no loss in light.

Rob.

[MarkH]

"STIG" <mancity@shaw.ca> wrote in
news:x20Ra.466934$Vi5.12110554@news1.calgary.shaw. ca:

> Shouldn't that be f2.0 allows twice as much light as f4 ?

No, you need to square the number for it to make sense:
F1 -> 1
F1.4 -> 2
F2 -> 4
F2.8 -> 8
F4 -> 16
F5.6 -> 32
F8 -> 64
etc

Each step represents 1 stop, halving the light as the number gets smaller.



--
Mark Heyes (New Zealand)
See my pics at [url]http://homepages.ihug.co.nz/~markh/[/url]
"There are 10 types of people, those that
understand binary and those that don't"

[STIG]

"MarkH" <markat@atdot.dot.dot> wrote in message
news:bf23hb$6ki$1@lust.ihug.co.nz...

> "STIG" <mancity@shaw.ca> wrote in
> news:x20Ra.466934$Vi5.12110554@news1.calgary.shaw. ca:
>

> > Shouldn't that be f2.0 allows twice as much light as f4 ?

>
> No, you need to square the number for it to make sense:
> F1 -> 1
> F1.4 -> 2
> F2 -> 4
> F2.8 -> 8
> F4 -> 16
> F5.6 -> 32
> F8 -> 64
> etc
>
> Each step represents 1 stop, halving the light as the number gets smaller.
>

Yes, you're right, don't know what I was thinking :0(

Rob.

[Don Stauffer]

Zoom lenses have a relative aperture that varies with focal length,
because some element of glass has a diameter that fixes the maximum
aperture diameter. However, the focal length varies depending on the
relative axial spacing of the elements. Since the f/# is the ratio of
focal length to aperture, the result is that it varies with focal
length. While may be possible to make a zoom lens that has a fixed
aperture stop, most do not.

bhaskar wrote:

>
> Hi,
> Many zoom lenses have a specification like
> f/2.8-4.0
> What does the range mean ?
> I know that one is max. aperture at wide angle end and
> another at tele end. But why do zoom lenses have two diff
> values ?
> Also when you say max. aperture is say e.g. f/2.8
> Does is mean that aperture can be opened max up to f/2.8
> i.e. f/22 to f/2.8 or that it can be closed only up f/2.8
> i.e f/2.0 to f/2.8 ?
>
> Also when max. shutter speed for a perticular lens/apperture is 1/1000 of a sec .
> Does it mean the shutter can't close any faster than 1/1000 of a sec or it
> can't close any slower than 1/1000th of a sec ?
>
> Many books are sometimes confusing on these terminologies, so i was hoping
> some pro can clear this up for me.
> thanks
> bhaskar

--
Don Stauffer in Minnesota
[email]stauffer@usfamily.net[/email]
webpage- [url]http://www.usfamily.net/web/stauffer[/url]