History Lesson

Richard · Sep 12, 2007

Okay so a student in my class asked our teacher why are they called f/stops? My teacher said he really didn't know but his guess was, back in the day when cameras where huge, the photographer most likely had an assistant to help adjust the lens in the front while the photographer would look through the lens. While telling his assistant to keeping turning he would then yell out "stop, right there!" So maybe that is where "stop" was introduced to photography lingo instead of f/step or f/position which I guess seem to make more sense. Anyone have a different theory or agree with my teacher?

Big Mike · Sep 12, 2007

The F number is a ratio between the aperture size and the focal length. It's sometimes called the Focal ratio...I'd guess that's where the F comes from.

Mike_E · Sep 12, 2007

A bit of Googleing...

Q3. What is meant by f-stop?
A. The focal length of the lens divided by the diameter of the aperture (as seen from the front). It is also called an f-number, and is written like f/8, which means the aperture diameter is 1/8th the focal length.
The term is used both in regard to the maximum aperture of a lens and in regard to the aperture selected in a specific situation.
The brightness of the image on the film is inversely proportional to the f-number squared. The depth of field increases but diffraction is worsened when using a large f-number. The effective f-number for all 3 effects changes if the lens is focused extremely close. See Q7.
The term "stops" purportedly comes from old technology in which the aperture was selected by turning a wheel with various sized holes in it, each one of which let in twice the light of the preceding one. Thus the phrase "open up a N stops" means to change to an aperture allowing in 2^N times as much light, and conversely with "stop down N stops".

Borrowed from photo.net

JC1220 · Sep 12, 2007

Sure hope he was not a photography teacher.:raisedbrow:

table1349 · Sep 12, 2007

Mike_E said:
A bit of Googleing...

Q3. What is meant by f-stop?
A. The focal length of the lens divided by the diameter of the aperture (as seen from the front). It is also called an f-number, and is written like f/8, which means the aperture diameter is 1/8th the focal length.
The term is used both in regard to the maximum aperture of a lens and in regard to the aperture selected in a specific situation.
The brightness of the image on the film is inversely proportional to the f-number squared. The depth of field increases but diffraction is worsened when using a large f-number. The effective f-number for all 3 effects changes if the lens is focused extremely close. See Q7.
The term "stops" purportedly comes from old technology in which the aperture was selected by turning a wheel with various sized holes in it, each one of which let in twice the light of the preceding one. Thus the phrase "open up a N stops" means to change to an aperture allowing in 2^N times as much light, and conversely with "stop down N stops".

Borrowed from photo.net

Give this man a CIGAR!!!

And a hearty congratulations. You just passed the test for this thread.
http://www.thephotoforum.com/forum/showthread.php?t=93489

Well done indeed Mike_E, Well Done.:thumbup:

Don Simon · Sep 12, 2007

Richard said:
My teacher said he really didn't know but his guess was, back in the day when cameras where huge, the photographer most likely had an assistant to help adjust the lens in the front while the photographer would look through the lens. While telling his assistant to keeping turning he would then yell out "stop, right there!"

... And when the assistant didn't listen, the photographer would shout "I said f****** stop!"... hence "f/ stops". :lmao: :lmao:

I much prefer this explanation to the real one.

JHF Photography · Sep 12, 2007

gryphonslair99 said:
Give this man a CIGAR!!! And a hearty congratulations. You just passed the test for this thread.
http://www.thephotoforum.com/forum/showthread.php?t=93489

Well done indeed Mike_E, Well Done.:thumbup:

ROFL :lmao::lmao::lmao::lmao::lmao:

Sweetsomedays · Sep 12, 2007

ZaphodB said:
... And when the assistant didn't listen, the photographer would shout "I said f****** stop!"... hence "f/ stops". :lmao: :lmao:

I much prefer this explanation to the real one.

WOOH!

Richard · Sep 12, 2007

Whoops... I wasn't clear about my question... but I'm glad I wasn't because I wouldn't have laughed like I did.

Anyway my teacher knows what the "f" in f/stop means, but could not give a 100% answer on why the word "stop" was used. Why not f/step or f/position. The google search by Mike_E I guess confirms what my teacher thinks. Which is while the assitant is turning the wheel the photographer at some point would say "stop" to the assitant which later on became as "go 2 stops up". Unless there is another theory? The search by Mike_E tells us what "stop" means now in f/stop but not why it is called a "stop".

But like I said I am really glad I wasn't clear on my question because that was funny.

abraxas · Sep 12, 2007

I think the 'f' is a mathematical symbol.

EOS_JD · Sep 13, 2007

Wikipedia is your friend......

The f-number [FONT=Georgia,serif]f/[/FONT]#, often notated as N, is given by

where f is the focal length, and D is the diameter of the entrance pupil. By convention, "[FONT=Georgia,serif]f/[/FONT]#" is treated as a single symbol, and specific values of [FONT=Georgia,serif]f/[/FONT]# are written by replacing the number sign with the value. For example, if the focal length is 16 times the pupil diameter, the f-number is [FONT=Georgia,serif]f/[/FONT]16, or N = 16. The greater the f-number, the less light per unit area reaches the image plane of the system.

Richard · Sep 13, 2007

EOS_JD,

I'm not sure if you read my second post in this thread, but I'm not asking what does "f/stop" means? I'm not asking what the "f" in "f/stop" means? I am wondering if anyone has a different theory about why the word "stop" was chosen instead of the word "step" or "position". Ok maybe this is how I should word it... Where did the word "stop" come from in "f/stop"?

For example if I were to ask where the phrase "sleep tight" came from, I don't want the answer "It means rest well"... I'm looking for

"This is a very well-used phrase in many parts of the English-speaking world. It's been common at bedtime for many years in the form of "good night, sleep tight, don't let the bedbugs bite", or similar.
There are several theories going the rounds as to the origin. One is that bedclothes were tied tightly to stop bedbugs biting. That's pure speculation and there seems to be no evidence whatsoever to support it."

Well unless there is a techincal reason then the answer would be different.

I just find it interesting to hear similar stories of the origin of phrases or lingo that is used so commonly now. And because my teacher could not come up with a technical reason why the word "stop" is used instead of "step" or "position" makes me think maybe he is right about his theory.

I know some people would say "who cares" but I thought I would post something that wasn't necessarily a technical question.

This is probably my fault sometimes I don't use the right words, but I hope this is clearer.

Richard · Sep 13, 2007

Wait a second wouldn't "stop" be used because it stops the amount of light hitting the film plane. Man that seems like an easy question now, but I am starting to question what kind of grades my teacher received in photography...:raisedbrow:

Don't I feel sheepish...:blushing:

abraxas · Sep 13, 2007

Oops...

elsaspet · Sep 13, 2007

Cool history lesson. I know what it means now, but have no idea on what the origin might mean. Hertz is a Photography Professor in the UK. Maybe he knows. Hertz?
Great question though.