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What is the difference between "Aperture" and "F-Stop"

 
 
Jack M
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      05-09-2005

Always wondered the same thing...Thanks for the info

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Neil Ellwood
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      05-09-2005
Gary Edstrom wrote:

> Ok, I think I have found the answer to my own question:
>
> And it involves MATH!
>
> Take the square root of 2.
>
> Raise it to the power of the aperature.
>
> The result is the F-Stop.
>
> I have tried this on several of my pictures and it works very
> precicely.
>
> Example: Aperture=6.9189 F-Stop=11
>
> (Sqrt(2))^6.9189 = 11.00014
>
> I have tried it on other pictures and it seems to work.
>
> On Mon, 09 May 2005 02:59:22 GMT, Gary Edstrom
> <(E-Mail Removed)> wrote:

That is a little more complicated than what I had always understood.

That the f no. = the number of tomes that the diameter of the aperture
will divide into the focal length of the lens.
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neil
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Gary Edstrom
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      05-09-2005
Here is a conversion table to convert from Aperture to F-Stop. This
seems to match the EXIF data generated by my Canon EOS 20D. Fractional
apertures would of course fall somewhere between 2 F-Stops. The term
"Aperture" as used in the EXIF header seems to be a much different
aperture than we would normally think of. It is a logarithmic scale.
Each increase of 1 unit on the aperture scale results in a cutting in
half of the light to the CCD.

Gary

Aperture F-Stop

0 1
1 1.4
2 2
3 2.8
4 4
5 5.6
6 8
7 11
8 16
9 22
10 32
11 45
12 64

On Mon, 09 May 2005 15:47:41 GMT, Gary Edstrom <(E-Mail Removed)>
wrote:

>Ok, I think I have found the answer to my own question:
>
>And it involves MATH!
>
>Take the square root of 2.
>
>Raise it to the power of the aperature.
>
>The result is the F-Stop.
>
>I have tried this on several of my pictures and it works very precicely.
>
>Example: Aperture=6.9189 F-Stop=11
>
>(Sqrt(2))^6.9189 = 11.00014
>
>I have tried it on other pictures and it seems to work.
>
>On Mon, 09 May 2005 02:59:22 GMT, Gary Edstrom <(E-Mail Removed)>
>wrote:
>
>>In looking at the EXIF headers of my pictures, I notice separate entries
>>for "Aperture" and F-Stop". Sometimes these entries are the same, and
>>sometimes they are different. I have tried looking it up in several
>>glossaries, but haven't found anything that really explains the
>>difference.
>>
>>Thanks, Gary


 
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Nostrobino
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      05-12-2005

"Paul Furman" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Gary Edstrom wrote:
>
>> In looking at the EXIF headers of my pictures, I notice separate entries
>> for "Aperture" and F-Stop". Sometimes these entries are the same, and
>> sometimes they are different. I have tried looking it up in several
>> glossaries, but haven't found anything that really explains the
>> difference.

>
>
> Aperture is the diameter of the opening, f/stop is aperture divided by
> focal length.


Other way around. Focal length divided by size of aperture.

For example, f/8 says the aperture size is f (the focal length) divided by
8.

N.


 
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Nostrobino
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      05-12-2005

"Gary Edstrom" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Ok, I think I have found the answer to my own question:
>
> And it involves MATH!
>
> Take the square root of 2.
>
> Raise it to the power of the aperature.
>
> The result is the F-Stop.
>
> I have tried this on several of my pictures and it works very precicely.
>
> Example: Aperture=6.9189 F-Stop=11
>
> (Sqrt(2))^6.9189 = 11.00014
>
> I have tried it on other pictures and it seems to work.


I'm not sure what you're doing there, but the standard f-stop series is
based on multiples of the square root of 2, such that each higher number
represents half the *area* of the aperture opening and thus passes half as
much light in the same period of time. (If it were half the *diameter* it
would have only one-fourth the area and thus pass one-fourth the amount of
light.)

Starting with 1, the series is 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16 and so on.
Thus f/2.8 passes half as much light as f/2 but twice as much as f/4, four
times as much as f/8 and so on. There are in-between stops of course.

N.


 
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Paul Furman
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      05-12-2005
Nostrobino wrote:
> "Paul Furman" <(E-Mail Removed)> wrote in message
>>
>>Aperture is the diameter of the opening, f/stop is aperture divided by
>>focal length.

>
>
> Other way around. Focal length divided by size of aperture.
>
> For example, f/8 says the aperture size is f (the focal length) divided by
> 8.



Ah, thanks, that explains the fractional expression of f-stop. Isn't
that nice when things make sense.


--
Paul Furman
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JPS@no.komm
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      05-13-2005
In message <(E-Mail Removed)>,
Jim Townsend <(E-Mail Removed)> wrote:

>F stop and aperture are essentially the same thing.. The aperture is
>measured in stops.


Not exactly. When aperture is referred to by an f-stop, you have to
know the focal length to know what the aperture actually is. Aperture
is measured in millimeters' f-stop is a ratio of focal length to
aperture.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <(E-Mail Removed)>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><

 
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Nostrobino
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      05-13-2005

"Nostrobino" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
>
> "Gary Edstrom" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
>> Ok, I think I have found the answer to my own question:
>>
>> And it involves MATH!
>>
>> Take the square root of 2.
>>
>> Raise it to the power of the aperature.
>>
>> The result is the F-Stop.
>>
>> I have tried this on several of my pictures and it works very precicely.
>>
>> Example: Aperture=6.9189 F-Stop=11
>>
>> (Sqrt(2))^6.9189 = 11.00014
>>
>> I have tried it on other pictures and it seems to work.

>
> I'm not sure what you're doing there, but the standard f-stop series is
> based on multiples of the square root of 2, such that each higher number
> represents half the *area* of the aperture opening and thus passes half as
> much light in the same period of time. (If it were half the *diameter* it
> would have only one-fourth the area and thus pass one-fourth the amount of
> light.)
>
> Starting with 1, the series is 1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16 and so
> on. Thus f/2.8 passes half as much light as f/2 but twice as much as f/4,
> four times as much as f/8 and so on.


Oops. That should have read, ". . . four times as much as f/5.6, eight times
as much as f/8 and so on."

N.

There are in-between stops of course.
>
> N.
>
>



 
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Nostrobino
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      05-13-2005

"Paul Furman" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Nostrobino wrote:
>> "Paul Furman" <(E-Mail Removed)> wrote in message
>>>
>>>Aperture is the diameter of the opening, f/stop is aperture divided by
>>>focal length.

>>
>>
>> Other way around. Focal length divided by size of aperture.
>>
>> For example, f/8 says the aperture size is f (the focal length) divided
>> by 8.

>
>
> Ah, thanks, that explains the fractional expression of f-stop. Isn't that
> nice when things make sense.


You're welcome, and yes it is.

N.


 
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