Why are they called f/stops?

[embdude]

We know what they are, how to use em', even how to calculate em', and even that they originally were not standard #'s among makers, but how the heck did they get that moniker?

???????????????????????????????

Why represented by a small f? Harkens back to some type of optical engineering term?

Did Waterhouse stops have a similar ratio? So if they came first why don't we have "W" stops...?

"Focal" seems the obvious term, since they relate to the focal legnth... However early photography was done in Europe, does "Focal Legnth" still translate with an F... but then why not a capitol letter....

Who made the first lenses with an adjustable iris? Or put f/ whatever on the barrell?????????

Anyone want to give it a shot?

[rent]

f for fraction of the focal length. -alex

[pierrot]

You are right, the small f does actually represent the focal length of the optical system (lens). It obviously became the symbol for the lens aperture by some aberration (and not a chromatic one!) in terminology.

Actually, the letter should be an N (for aperture Number) defined as N=f/O
where f is the focal length and O is the aperture diaphragm i.e. the diameter of the iris diaphragm.

For some reason, instead of using the N, the choice was made for the f and the / division sign... which makes in fact perfect sense as for the typo of the moniker, since the N number is resulting from a division.

The stops are set in a geometric progression because the amount of light passing through the lens is proportional to the square of the diaphragm diameter: a diameter twice larger gives an aperture area 4 times bigger thus allowing 4 times more light to pass through the lens/enter the camera. That is the reason why the stop are set in a progression based on a x1.4 factor (square root of 2).
Should be 1.4142135623730950488016887242097 actually, but this is a bit too long to be engraved on a lens barrel. ;)

As for the 1st manufacturer to have used the f/ symbol on their lenses, I must apologize for my ignorance...

[lancea]

The Life book "The Camera" reckons that Johann Zahn had an adjustable aperture on his portable camera around the end of the 17th century. In which case, it actually pre-dates photography as we know it because it was a camera obscura (people traced the images). As to who first manufactured a camera with an "f" I know not, but I guess a popular answer would be Canon ;)

[andygrif]

I thought the 'f' stood for 'fernetre' the French for Window.

[ron chappel]

Should be 1.4142135623730950488016887242097 actually, but this is a bit too long to be engraved on a lens barrel. ;)

I dunno-some of these manufacturers manage to fit a shed load of letters on there!

[Curtis N]

From the book Digital Cinematography & Directing by Dan Ablan:
"The origin of the lower case "f" in f-stop goes back to 1932 and renowned photographer Ansel Adams. He and a few others, Willard Van Dyke, Imogen Cunningham, Edward Weston, Hentry Swift, Sonya Noskowiak, and John Paul Edwards, formed a group called f.64. This group was dedicated to pure photography, including portraits and landscapes. Van Dyke originally proposed the name US256, but Adams thought it sounded like a highway. He simply wrote an "f" and then put a dot similar to the old aperture settings. They soon updated this to an f with a slash mark to read Group f/64."

[schmoelzel]

And here I thought the f stood for 'friggin expensive'..........:D

[embdude]

I'm rather happy with this explanation as to the origins...

In search of the origin of the f-stop (http://webphotoresource.blogspot.com/)
"For some time I have wondered how it is that we have come to call the aperture of a lens the f-stop. I have run into a myriad of various explanations but none have been completely satisfying or seemed entirely plausible.

I had assumed that it came from a scientific or mathematical expression, and indeed I believe I have found that formula.

f/# = N = f/D

Where f is the focal length, and D is the diameter of the entrance pupil. By convention, "f/#" is treated as a single symbol, and specific values of f/# are written by replacing the number sign with the value."

I still wonder about who was the first to put it on the lens barrel?


I suppose sense the Camera Obscura had models with stoppable lens apertures it might in fact be the first and then merely adopted into the world of photography.

[wimg]

BTW, the word "stop" in the term f/stop is derived from the fact that with older manual lenses, you have to set the aperture number, and it actually clicks in, stops IOW, at that number, and closes the diaphragm to that particular f/stop.

And yes, f/stops were already marked on lenses early on in photography, not on all early lenses, though, especially as some didn't even have diaphragms.

Kind regards, Wim

[DaveG]

STOP comes from the pre-diaphragm aperture control, which were plates or disks with a drilled hole in the centre, and were called Waterhouse Stops. These came in sets with each one having a different size "hole" or aperture. These plates allowed light to pass through them, but they also "stopped" a certain amount of light too, hence the name. I have no idea as to whether they went in front of or behind the lens, or even inside where modern diaphragms are located, but as far as I know that's where Stops came from.

[wimg]

STOP comes from the pre-diaphragm aperture control, which were plates or disks with a drilled hole in the centre, and were called Waterhouse Stops. These came in sets with each one having a different size "hole" or aperture. These plates allowed light to pass through them, but they also "stopped" a certain amount of light too, hence the name. I have no idea as to whether they went in front of or behind the lens, or even inside where modern diaphragms are located, but as far as I know that's where Stops came from.
Hi Dave,

Interesting, thanks for sharing. I didn't know that. Got a book on optics in my native tongue where they say it was from the diaphragm click stops.

Kind regards, Wim

[WMS]

For anyone interested this link is to the wikipedia page on f-numbers

http://en.wikipedia.org/wiki/F_stop

WMS

[embdude]

For anyone interested this link is to the wikipedia page on f-numbers

http://en.wikipedia.org/wiki/F_stop

WMS

Thanks! :D:D

What a mess it was back then...
Here is the situation as seen in 1899:
http://upload.wikimedia.org/wikipedia/en/5/52/DiaphragmNumbers.gif (http://en.wikipedia.org/wiki/Image:DiaphragmNumbers.gif)

[embdude]

The photo industry really benefited so much from organizations like the ASA (now ISO) and JCII.....

[thekid24]

Theyre called f/ stops because alot of newbies would say "Fu(n)k I forgot to stop it down",lol.

I could be wrong though:|:p

[joruiz]

Theyre called f/ stops because alot of newbies would say "Fu(n)k I forgot to stop it down",lol.

I could be wrong though:|:p

yeah, I say that a lot, si that must be it... :P