# super noob question. is f2.8 = f/2.8??

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#### deepblue2

##### New Member
hi guys, and pardon if this question has been asked before. i tried searching clubsnap as well as google but it just keeps getting me more frustrated.

i'm trying to learn up on aperture and shutter settings. but different sites give different notations. some give f2.8, others give f/2.8. are they the same? if yes then y the difference in notation?

i'm aware that a larger aperture results in a shallower depth-of-field. but the f/2.8 (f * 1/2.8??) thing really confuses me.

West_ray said:
yeah same ~~~

thanks so much.

sama-sama dude

#### tingchiyen

##### New Member
It's the same thing. f2 = f/2, it's just a matter of notation.
The f/x system is actually a ratio figure, not an absolute measurement, that's why an f/2 setting on a 50mm lens and an f/2 setting on a 100mm lens admits exactly the same amount of light. That's why it's sometimes noted as a fraction and other times as an f-stop number just for convenience.

#### deepblue2

##### New Member
tingchiyen said:
It's the same thing. f2 = f/2, it's just a matter of notation.
The f/x system is actually a ratio figure, not an absolute measurement, that's why an f/2 setting on a 50mm lens and an f/2 setting on a 100mm lens admits exactly the same amount of light. That's why it's sometimes noted as a fraction and other times as an f-stop number just for convenience.
ahh.. ok.. need to go read up more on that. thanks

jbma: nice quote.. trying to do that. but it seems life itself doesn't want to let me do it..

#### Astin

##### Senior Member
Actually it is 1/the square root of 1,2,4,8,16,32,etc. Its in most Physics textbook.

#### RemAcuTetigisti

##### New Member
Bingo. F-Stops are fractions and fyi, vary in square roots of 2. As Astin puts it, any decent Physics text book (if you are intimidated, any good intro to photography book) will speak volumes about this subject. It is correct to use f/2.8 but photographers implicitly inderstand when one says 2.8 (no f or /) and one just needs to know the relation between the f-stop numbers and the amount of light allowed.

#### Astin

##### Senior Member
Haha you are right friend, I love Physics.
The *most correct* way to say is:
"The f-stop is 1/2.8 or 1/4 or 1/5.6"
Somehow it got shorten to "f/2.8 or f/4 or f/5.6"
Then some more how it got shorten to "f2.8, f4, f5.6"

#### deepblue2

##### New Member
Astin said:
Haha you are right friend, I love Physics.
The *most correct* way to say is:
"The f-stop is 1/2.8 or 1/4 or 1/5.6"
Somehow it got shorten to "f/2.8 or f/4 or f/5.6"
Then some more how it got shorten to "f2.8, f4, f5.6"
roger that. thanks. surprising how none of the websites bothered to explain this.

#### Astin

##### Senior Member
Ok, now you go and find out what does the letter "f" stand for?
(Give you something to do on a boring Thursday afternoon )

#### deepblue2

##### New Member
Astin said:
Ok, now you go and find out what does the letter "f" stand for?
(Give you something to do on a boring Thursday afternoon )
heh heh heh.. THAT i read up before... it stands for focal length right?

#### mervlam

##### Senior Member
Astin said:
Actually it is 1/the square root of 1,2,4,8,16,32,etc. Its in most Physics textbook.
since, i'm bored to extremes and curious now, which topic in the Physics textbook you can find this? My general Physics text reference book dont seem to have such a topic... or is it that i dont open my eyes wide enough?

#### deepblue2

##### New Member
mervlam said:
since, i'm bored to extremes and curious now, which topic in the Physics textbook you can find this? My general Physics text reference book dont seem to have such a topic... or is it that i dont open my eyes wide enough?
heh heh heh.. may not be a SPECIFIC chapter but u might find some useful info in the optics chapters.

mind u i have not touched a physics book since i left uni about 4 years ago. and even towards the later stages i used less and less of it.

#### Astin

##### Senior Member
mervlam said:
since, i'm bored to extremes and curious now, which topic in the Physics textbook you can find this? My general Physics text reference book dont seem to have such a topic... or is it that i dont open my eyes wide enough?

#### mervlam

##### Senior Member
Astin said:
which one???

A Levels Physics
or NTU Year 1 G166 Engineering Physics?

punt intended... :blah:

er.. jokes aside, i didn't really noticed that the topic of aperture is taught in 1st year university physics, unless you are specialising in optics in either EE or Mech.

what was taught was mostly appliable to EM wave theory, eg., diffraction, convergence, blah blah blah.

#### Noir

##### New Member
And apart from F-stop, there is something called T-stop too. Know what it is ?

#### deepblue2

##### New Member
Noir said:
And apart from F-stop, there is something called T-stop too.
which is??

#### Astin

##### Senior Member
Let me recall what it was.....it was many many (?) years ago already.....

In A level physics (and also repeated in Uni year 1 Engineering Physics), there was a section on "Optics", it taught about what is a convergent lens, and how image from infinity will form a shadow image after passing through a convergent lens, and how a upright image will become a upside down image, and how to calculate how much light will require using the lens index blah blah blah.....(this made me become interested in photography.)

If I remember correctly, it also taught something about using multiple lens together, and about the lens coating elements, and many other little things inside the camera lens.

#### justarius

##### Senior Member
Noir said:
And apart from F-stop, there is something called T-stop too. Know what it is ?
Think T-stop measures the actual light tranmission at the end of the lens, and is used mainly in the movie industry. But for all practical purposes, T-stop is roughly equivalent to f-stop.

did i hit the jackpot?

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