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Canon 10D Learning Curve

 
 
Michalkun
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Posts: n/a
 
      08-01-2003
Todd Walker <(E-Mail Removed)> wrote in
news:(E-Mail Removed):

> Yes. And get your wallet ready. The widest EF zoom is the 16-35 f/2.8L
> and it's around $1400. The widest EF prime is the 14mm f/2.8L and it's
> $1800. If you are willing to sacrifice a little bit on the wide end,
>


I need to know one more thing. What do the numbers mean after f? Is that
aperture? Can't seem to find any sensible basic information about it.
 
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Todd Walker
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      08-01-2003
In article <Xns93CAA1C9B177Dmichalkunyahoocom@130.133.1.4>, buranko2000
@yahoo.com says...
> Todd Walker <(E-Mail Removed)> wrote in
> news:(E-Mail Removed):
>
> > Yes. And get your wallet ready. The widest EF zoom is the 16-35 f/2.8L
> > and it's around $1400. The widest EF prime is the 14mm f/2.8L and it's
> > $1800. If you are willing to sacrifice a little bit on the wide end,
> >

>
> I need to know one more thing. What do the numbers mean after f? Is that
> aperture? Can't seem to find any sensible basic information about it.
>


Yes, that's the aperture. The aperture number is an indication of the
size of the aperture opening as a reciprocal of the focal length. So, an
aperture of f/2.0 means that the aperture opening is 1/2 the size of the
focal length. If your focal length is 100mm, the aperture opening is
50mm. If the aperture is f/4.0 with the 100mm lens, the aperture is
25mm.

--
________________________________
Todd Walker
http://twalker.d2g.com
Canon 10D
My Digital Photography Weblog:
http://twalker.d2g.com/dpblog.htm
_________________________________
 
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David Grandy
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Posts: n/a
 
      08-01-2003
To clear up a couple of things: The mechanism inside the lens is a
diaphragm. The hole it creates is the aperture. F numbers (written with a
small or italic "f" refer to lens openings also known as lens apertures, or
f-stops.

They do appear at first to be completely non-sensible. The bigger the hole
(aperture) the smaller the number. But F-stops are really ratios and this
makes the big hole/large number make one heck of a lot more sense. For
example 2.8 is really 1:2.8; and 16 is really 1:16 and of course then 1:16
will have a smaller hole than 1:2.8. The only place you will see these
numbers written as ratios is on the front of your lens where it will say
something like "Nikkor 50mm 1:1.4". And he simple reason for that is that
there isn't room on the lens to write in the 1:whatever on the aperture ring
or on the LCD, and this is also true with the way the 1 is dropped off 1/250
of a second shutterspeed, and is just written 250.

The reason that these aperture numbers don't make much sense is that they
are not progressions like 125, 250, 500, 1000 as are shutterspeeds. F-stops
are more or less measuring area which doesn't correspond in the same way.
But you should treat these aperture numbers/f-stops as whole numbers. 1,
1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22 ... Do not round off 1.4, 2.8, 5.6.
They exist as whole numbers and real photographers will laugh at you if you
try to talk about f6 when you mean f5.6. After awhile apertures/f-stops will
be as common to you as the alphabet, except you will be able to go backwards
as well as forward with f-stops.

F or written as a small f, means - as far as I can tell - function. Not
film or anything like that but the math term function. And apertures are
mathematical relationships, not transmission characteristics. You take the
exit pupil size (more or less the lens without any diaphragm effect) and
let's say that number is 25 mm. You divide that number into the focal
length of the lens, say 50mm; and get an answer of 2. That is an f2 lens
wide open. It's also why if you add a two times converter you lose two
stops of light. See the exit pupil hasn't changed but the focal length has:
100 (new focal length) / 25 = 4 or f4.

Movie camera lenses where hundreds of thousands of dollars of film are shot
behind them, are NOT marked in f-stops (math) but in t-stops (for
transmission) and each one of those lenses are individually calibrated. For
regular still photography, f-stops will get you close enough!

When you look at ISO numbers or shutterspeeds there is a clear relationship
where the speeds double or half themselves depending on which way you
travel. Think of each jump as a unit, or in photo-speak a "stop". So ISO
100 is one "stop" more sensitive to light than ISO 50. 1/250 of a second
lets in one stop more light than 1/500. With the f-stops, which (once
again) we treat as whole numbers there is the same unit or stop difference
as we go from 2.8 to 4 or 11 to 16. The difference between each adjacent
f-stop, shutterspeed and ISO is ONE STOP. By looking at it this way we can
compare apples to oranges since if we let in one stop more light with our
shutter we can let in one stop less light with our aperture.

Here's the next step. Pretend that you pick up your camera and the aperture
is at f5.6 and the shutterspeed is 1/250 and you are using an ISO 400 film
(or digital ISO). As if by magic this happens to be the correct exposure,
or at least the meter in your camera tells you that it is. Now if you go
from 1/250 to 1/125 you've let in ONE STOP more light and you've
over-exposed. But if you change the aperture to f8 you've let in ONE STOP
less light and the exposure remains correct. The point is that as you let
in more or less light with the shutter you can compensate with the aperture
(or vice versa) because you are speaking in the same "stops".

Obviously this example of 1/250 @ f5.6 with ISO 400 is only correct if
that's the light situation you actually have and you almost always have to
change exposures to take into account the real light situation. If you
change ISO's you will have to make adjustments as well since 1/250 @ f5.6
may be right for ISO 400, but if you used ISO 200 film/capture then you've
underexposed by a stop.

So for what reasons do you make specific aperture/shutterspeed/ISO choices?
Well the higher the ISO the greater the sensitivity of the film or capture,
but the grainier or "noisier" the results. With shutterspeeds the higher
(faster) the shutterspeed the more "freezing" of action takes place, so you
might want to use fast shutterspeeds to photograph sports.

Then there's the aperture. Not only does it let more or less light into the
camera but it also has an effect on the image. When you look at something
with your eyes- say 10 feet away - it's in focus. Behind this focus point
and in front of it, everything is out of focus. But if you glance at
something closer, your eyes (really your brain) refocuses so fast that you
never noticed that it was out of focus to begin with. Lenses are too slow
and stupid for that. When you focus a lens, there is a plane - parallel
with the back of the camera (and large format photographers forgive me for
putting it this way) - that is in focus. This plane has a depth. If you
use a large lens opening (say f2) then this plane is very shallow. If you
use a small lens opening (f16) this plane may be very deep. This plane of
"in focus" is called the depth of field.

As a photographer you have to decide on what you need. If I'm shooting
sports I shoot at fast shutterspeeds so I can freeze the action, and I'm not
all that concerned about depth of field. However if I'm shooting a group,
with three rows of subjects, then I have to be concerned about the depth. I
mean I NEED all three rows to be sharp and I'll use a smaller (f8- f16)
aperture to assure that, even if it means a slower shutterspeed. I can also
choose a faster (more light sensitive) film to hep me get a higher
shutterspeed or smaller aperture, although I pay a price for the higher
grain.

Once you know this aperture/shutterspeed/ISO stuff and how it affects your
images then you are to paraphrase Winston Churchill " ... not at the
beginning of the end, but the end of the beginning." of your photographic
journey.


 
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Johnny B Good
Guest
Posts: n/a
 
      08-02-2003
The message <W2DWa.51388$(E-Mail Removed)>
from "David Grandy" <(E-Mail Removed)> contains these words:

> To clear up a couple of things: The mechanism inside the lens is a
> diaphragm. The hole it creates is the aperture. F numbers (written with a
> small or italic "f" refer to lens openings also known as lens apertures, or
> f-stops.


> They do appear at first to be completely non-sensible. The bigger the hole
> (aperture) the smaller the number. But F-stops are really ratios and this
> makes the big hole/large number make one heck of a lot more sense. For
> example 2.8 is really 1:2.8; and 16 is really 1:16 and of course then 1:16
> will have a smaller hole than 1:2.8. The only place you will see these
> numbers written as ratios is on the front of your lens where it will say
> something like "Nikkor 50mm 1:1.4". And he simple reason for that is that
> there isn't room on the lens to write in the 1:whatever on the aperture ring
> or on the LCD, and this is also true with the way the 1 is dropped off 1/250
> of a second shutterspeed, and is just written 250.


> The reason that these aperture numbers don't make much sense is that they
> are not progressions like 125, 250, 500, 1000 as are shutterspeeds. F-stops
> are more or less measuring area which doesn't correspond in the same way.
> But you should treat these aperture numbers/f-stops as whole numbers. 1,
> 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22 ... Do not round off 1.4, 2.8, 5.6.
> They exist as whole numbers and real photographers will laugh at you if you
> try to talk about f6 when you mean f5.6. After awhile apertures/f-stops will
> be as common to you as the alphabet, except you will be able to go backwards
> as well as forward with f-stops.


> F or written as a small f, means - as far as I can tell - function. Not
> film or anything like that but the math term function. And apertures are
> mathematical relationships, not transmission characteristics. You take the
> exit pupil size (more or less the lens without any diaphragm effect) and
> let's say that number is 25 mm. You divide that number into the focal
> length of the lens, say 50mm; and get an answer of 2. That is an f2 lens
> wide open. It's also why if you add a two times converter you lose two
> stops of light. See the exit pupil hasn't changed but the focal length has:
> 100 (new focal length) / 25 = 4 or f4.


> Movie camera lenses where hundreds of thousands of dollars of film are shot
> behind them, are NOT marked in f-stops (math) but in t-stops (for
> transmission) and each one of those lenses are individually calibrated. For
> regular still photography, f-stops will get you close enough!


> When you look at ISO numbers or shutterspeeds there is a clear relationship
> where the speeds double or half themselves depending on which way you
> travel. Think of each jump as a unit, or in photo-speak a "stop". So ISO
> 100 is one "stop" more sensitive to light than ISO 50. 1/250 of a second
> lets in one stop more light than 1/500. With the f-stops, which (once
> again) we treat as whole numbers there is the same unit or stop difference
> as we go from 2.8 to 4 or 11 to 16. The difference between each adjacent
> f-stop, shutterspeed and ISO is ONE STOP. By looking at it this way we can
> compare apples to oranges since if we let in one stop more light with our
> shutter we can let in one stop less light with our aperture.


> Here's the next step. Pretend that you pick up your camera and the aperture
> is at f5.6 and the shutterspeed is 1/250 and you are using an ISO 400 film
> (or digital ISO). As if by magic this happens to be the correct exposure,
> or at least the meter in your camera tells you that it is. Now if you go
> from 1/250 to 1/125 you've let in ONE STOP more light and you've
> over-exposed. But if you change the aperture to f8 you've let in ONE STOP
> less light and the exposure remains correct. The point is that as you let
> in more or less light with the shutter you can compensate with the aperture
> (or vice versa) because you are speaking in the same "stops".


> Obviously this example of 1/250 @ f5.6 with ISO 400 is only correct if
> that's the light situation you actually have and you almost always have to
> change exposures to take into account the real light situation. If you
> change ISO's you will have to make adjustments as well since 1/250 @ f5.6
> may be right for ISO 400, but if you used ISO 200 film/capture then you've
> underexposed by a stop.


> So for what reasons do you make specific aperture/shutterspeed/ISO choices?
> Well the higher the ISO the greater the sensitivity of the film or capture,
> but the grainier or "noisier" the results. With shutterspeeds the higher
> (faster) the shutterspeed the more "freezing" of action takes place, so you
> might want to use fast shutterspeeds to photograph sports.


> Then there's the aperture. Not only does it let more or less light into the
> camera but it also has an effect on the image. When you look at something
> with your eyes- say 10 feet away - it's in focus. Behind this focus point
> and in front of it, everything is out of focus. But if you glance at
> something closer, your eyes (really your brain) refocuses so fast that you
> never noticed that it was out of focus to begin with. Lenses are too slow
> and stupid for that. When you focus a lens, there is a plane - parallel
> with the back of the camera (and large format photographers forgive me for
> putting it this way) - that is in focus. This plane has a depth. If you
> use a large lens opening (say f2) then this plane is very shallow. If you
> use a small lens opening (f16) this plane may be very deep. This plane of
> "in focus" is called the depth of field.


> As a photographer you have to decide on what you need. If I'm shooting
> sports I shoot at fast shutterspeeds so I can freeze the action, and I'm not
> all that concerned about depth of field. However if I'm shooting a group,
> with three rows of subjects, then I have to be concerned about the depth. I
> mean I NEED all three rows to be sharp and I'll use a smaller (f8- f16)
> aperture to assure that, even if it means a slower shutterspeed. I can also
> choose a faster (more light sensitive) film to hep me get a higher
> shutterspeed or smaller aperture, although I pay a price for the higher
> grain.


> Once you know this aperture/shutterspeed/ISO stuff and how it affects your
> images then you are to paraphrase Winston Churchill " ... not at the
> beginning of the end, but the end of the beginning." of your photographic
> journey.


Aha! *Now* I understand the saying "Teaching Granny to Suck Eggs"

--
Regards, John.

To reply directly, please remove "buttplug" .Mail via the
"Reply Direct" button and Spam-bots will be rejected.

 
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Todd Walker
Guest
Posts: n/a
 
      08-02-2003
In article <(E-Mail Removed)>,
http://www.velocityreviews.com/forums/(E-Mail Removed) says...
> Aha! *Now* I understand the saying "Teaching Granny to Suck Eggs"
>


John,

You are probably new to Usenet and don't know the etiquette -- please
don't quote a 113 line message to add one line of your own...

Just trying to help!

Todd

--
________________________________
Todd Walker
http://twalker.d2g.com
Canon 10D
My Digital Photography Weblog:
http://twalker.d2g.com/dpblog.htm
_________________________________
 
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Bryan Olson
Guest
Posts: n/a
 
      08-02-2003
David Grandy wrote:

> F-stops are really ratios and this
> makes the big hole/large number make one heck of a lot more sense. For
> example 2.8 is really 1:2.8; and 16 is really 1:16 and of course then

1:16
> will have a smaller hole than 1:2.8. The only place you will see these
> numbers written as ratios is on the front of your lens where it will say
> something like "Nikkor 50mm 1:1.4".


They actually get written as ratios very frequently, and it's definitely
the correct way to write them; "f/2.8" is much better than "f2.8".

[...]
> F or written as a small f, means - as far as I can tell - function. Not
> film or anything like that but the math term function.


No, the 'f' means focal-length. The aperture f/2.8 literally
means that the aperture (diameter of the objective pupil) is
equal to the focal-length divided by 2.8.

> And apertures are
> mathematical relationships, not transmission characteristics. You

take the
> exit pupil size (more or less the lens without any diaphragm effect) and
> let's say that number is 25 mm. You divide that number into the focal
> length of the lens, say 50mm; and get an answer of 2. That is an f2 lens
> wide open. It's also why if you add a two times converter you lose two
> stops of light. See the exit pupil hasn't changed but the focal

length has:
> 100 (new focal length) / 25 = 4 or f4.


Right idea, but let's sweat the details. First, an aperture is
a diameter, a linear distance measurable in mm or inches or
furlongs. It's the diameter of entry pupil, not the exit pupil;
for a lens with a diaphragm, it's the diameter of the image of
the diaphragm opening viewed through the objective.

So if our aperture is f/4, and our focal length is 100mm, then
our aperture is 25mm. Since 'f' means focal-length, we
substitute the actual focal-length 100mm into 'f/4' to get

100mm / 4 = 25mm.

Both the number and the units work.

So why do we say the aperture is f/4 rather than saying it's
25mm? What we're usually trying to compute is the intensity of
light delivered to the film (or detector chip). For a given
subject and illumination, the amount of light on a particular
area of film is proportional to the square of the aperture, and
inversely proportional to the square of the focal length. The
ratio captures both in one number.


On final question: why do we express the ratio as focal-length
over aperture, and not aperture over focal-length. Wouldn't
the latter make more sense, since larger values of the ratio
mean more light on the film? Well, I believe this is merely an
accident of history. Aperture/focal_length would have been more
convenient for photographers, but it's too late to change now.


--
--Bryan

 
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Todd Walker
Guest
Posts: n/a
 
      08-02-2003
In article <JjOWa.51535$(E-Mail Removed)>,
(E-Mail Removed) says...
> >They actually get written as ratios very frequently, ...<

>
> Not on the lens or camera they don't.


Wrong. Look at this picture:

http://twalker.d2g.com/canon10d/me_and_10d.jpg

Notice on the lens at about the 2:00 position, it says "1:3.5-4.5 IS."
Look at the markings on just about any lens in existence and you will
see the same thing.

--
________________________________
Todd Walker
http://twalker.d2g.com
Canon 10D
My Digital Photography Weblog:
http://twalker.d2g.com/dpblog.htm
_________________________________
 
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Michalkun
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Posts: n/a
 
      08-05-2003
That was a great explanation!
Thanks a lot. I really appreciate it.

 
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