Velocity Reviews > What is the difference between "Aperture" and "F-Stop"

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

Jack M
Guest
Posts: n/a

 05-09-2005

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

--
Jack
-----------------------------------------------------------------------
Jack M's Profile: http://thephotostation.net/forums/member.php?userid=209
View this thread: http://thephotostation.net/forums/showthread.php?t=1269

Neil Ellwood
Guest
Posts: n/a

 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.
--
neil
delete delete to reply

Gary Edstrom
Guest
Posts: n/a

 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

Nostrobino
Guest
Posts: n/a

 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.

Nostrobino
Guest
Posts: n/a

 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.

Paul Furman
Guest
Posts: n/a

 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
http://www.edgehill.net/1
san francisco native plants

JPS@no.komm
Guest
Posts: n/a

 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)>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><

Nostrobino
Guest
Posts: n/a

 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.
>
>

Nostrobino
Guest
Posts: n/a

 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.

 Thread Tools

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are Off Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post PerlFAQ Server Perl Misc 0 04-15-2011 04:00 AM PerlFAQ Server Perl Misc 0 01-06-2011 05:00 PM arnuld C++ 33 03-05-2007 03:11 PM jakk ASP .Net 4 03-22-2005 09:23 PM Santa C Programming 1 07-17-2003 02:10 PM

Advertisments