aperature number vs f number

F stops I get.

at f13 I have an apeture number of 7.3

Is it the same thing but a different scale or is it different.

What is the scale if the same thing? (like say Kelvin and Celsius?)

There's no such thing as an aperture number.

Aperture is numbered in f/stops. eg. f/2.8, f/5.6, f/11, f/16

The lower the f/stop the bigger the physical aperture is. And vice-versa.

Here's a guide:

f-stops are merely fractions. For example, f/8 means the aperture (opening) in the lens is 1/8 of its focal length. f/11 is 1/11 of the focal length, and so on. It's just a ratio.

That's why as the number gets larger, the opening -- and amount of passed light -- gets smaller. If you'll do the arithmetic you'll see that an aperture (circle) that's twice as large as another one will admit 4x the light. Conversely, an aperture half as large will admit 1/4 the light.

Len Philpot wrote:

f-stops are merely fractions. For example, f/8 means the aperture (opening) in the lens is 1/8 of its focal length. f/11 is 1/11 of the focal length, and so on. It's just a ratio.

That's why as the number gets larger, the opening -- and amount of passed light -- gets smaller. If you'll do the arithmetic you'll see that an aperture (circle) that's twice as large as another one will admit 4x the light. Conversely, an aperture half as large will admit 1/4 the light.

I didn't know that.

Thanks for the tip. 

Jethro B-UK wrote:

Len Philpot wrote:

f-stops are merely fractions. For example, f/8 means the aperture (opening) in the lens is 1/8 of its focal length. f/11 is 1/11 of the focal length, and so on. It's just a ratio.

That's why as the number gets larger, the opening -- and amount of passed light -- gets smaller. If you'll do the arithmetic you'll see that an aperture (circle) that's twice as large as another one will admit 4x the light. Conversely, an aperture half as large will admit 1/4 the light.

I didn't know that.

Thanks for the tip.

In my other hobby of astronomy, we deal with f/ratios all the time. A 10 inch f/5 telescope has an aperture of 10 inches (254mm) and a focal length of 50 inches (1270mm). A 10 inch f/10 scope would have twice the focal length and therefore twice the magnification with the same eyepiece, but it collects the same amount of light. Focal ratios are static since almost never is the aperture variable on a telescope. It's the same relationship as with a camera lens, just a slightly different context.

"Faster", i.e., lower f number, telescopes are currently en vogue, but they're much more difficult (and expensive!) to make and are far more demanding on eyepiece / corrector design and quality.

In astronomy there's far less interest in DOF since everything is focused at infinity. But there's interest in things like true field of view, exit pupil, image brightness, etc.

Toronto Photography wrote:

F stops I get.

at f13 I have an apeture number of 7.3

Is it the same thing but a different scale or is it different.

What is the scale if the same thing? (like say Kelvin and Celsius?)

The "aperture number" of 7.3 is the number of stops smaller f/13 is compared to f/1.0

SquareRoot(2) ^ "aperture number" = f/#   ("^" means raised to power or exponent)

Sqrt(2)^1 = f/1.4

Sqrt(2)^2 = f/2.0

...

Sqrt(2)^7.333 = f/13 (12.7)

Sqrt(2)^7.667 = f/14 (14.2)

Sqrt(2)^8 = f/16

Lemming51 wrote:

Toronto Photography wrote:

F stops I get.

at f13 I have an apeture number of 7.3

Is it the same thing but a different scale or is it different.

What is the scale if the same thing? (like say Kelvin and Celsius?)

The "aperture number" of 7.3 is the number of stops smaller f/13 is compared to f/1.0

SquareRoot(2) ^ "aperture number" = f/# ("^" means raised to power or exponent)

Sqrt(2)^1 = f/1.4

Sqrt(2)^2 = f/2.0

...

Sqrt(2)^7.333 = f/13 (12.7)

Sqrt(2)^7.667 = f/14 (14.2)

Sqrt(2)^8 = f/16

That's the first time I've heard it expressed that way. To me it's far more convenient (and meaningful) to just think of it terms of stops (or half-stops, third-stops, etc. depending on your preference and camera settings). Makes doing the mental math easier, if and when required. YMMV.

Jethro B-UK wrote:

There's no such thing as an aperture number.

Aperture is numbered in f/stops. eg. f/2.8, f/5.6, f/11, f/16

The lower the f/stop the bigger the physical aperture is. And vice-versa.

Here's a guide:

Thats not true. META DATA has "Apeture" which is different from F tops. as both are listed. They appear to have an inverse relation.

In future you might want to say you never heard of it rather than gaslighing.

Lemming51 wrote:

Toronto Photography wrote:

F stops I get.

at f13 I have an apeture number of 7.3

Is it the same thing but a different scale or is it different.

What is the scale if the same thing? (like say Kelvin and Celsius?)

The "aperture number" of 7.3 is the number of stops smaller f/13 is compared to f/1.0

SquareRoot(2) ^ "aperture number" = f/# ("^" means raised to power or exponent)

Sqrt(2)^1 = f/1.4

Sqrt(2)^2 = f/2.0

...

Sqrt(2)^7.333 = f/13 (12.7)

Sqrt(2)^7.667 = f/14 (14.2)

Sqrt(2)^8 = f/16

Ok what is the "Aperture number" actually called and what is it used for?

i suspect that the apertue number would have made more sense if it was standard as the bigger the number seems to have more light as oppose to the denomintor of a fraction. And I suspect someone uses it just like some people use Kelvin and people used to use and maybe in the USA still use the Rankine scale.

Trivia question did white balance use the Rankine scale first then switch?

Toronto Photography wrote:

Jethro B-UK wrote:

...

Thats not true. META DATA has "Apeture" which is different from F tops. as both are listed. They appear to have an inverse relation.

My canons don't.

Could you provide an example (perhaps a screenshot)?

In future you might want to say you never heard of it rather than gaslighing.

Pardon?

Toronto Photography wrote:

Jethro B-UK wrote:

There's no such thing as an aperture number.

Aperture is numbered in f/stops. eg. f/2.8, f/5.6, f/11, f/16

The lower the f/stop the bigger the physical aperture is. And vice-versa.

Here's a guide:

Thats not true. META DATA has "Apeture" which is different from F tops. as both are listed. They appear to have an inverse relation.

What software/system is showing you this META DATA?

In future you might want to say you never heard of it rather than gaslighing.

This video does not referance Aperture Number, only F Stops/F Numbers* in a way that most photographers are very familiar.

* Some refer to F11 as f/11, the latter making it more obvious that it is an inverse relationship, ie the bigger the number the small the opening. My Canon lenses simply have 1:2.8 etc, but F2.8 is fine once the convention is understood. Canon's DPP software shows for example: Av(Aperture Value) 7.1

In 50+ years I have never seen Aperture Number as you have described and has been explained elsewhere so I don't think I've missed anything

AnthonyL wrote:

Toronto Photography wrote:

Jethro B-UK wrote:

...

Thats not true. META DATA has "Apeture" which is different from F tops. as both are listed. They appear to have an inverse relation.

What software/system is showing you this META DATA?

That's what I want to know.

In future you might want to say you never heard of it rather than gaslighing.

... (video)

In 50+ years I have never seen Aperture Number as you have described and has been explained elsewhere so I don't think I've missed anything

Oh few! I thought I might have missed something fundamental.

Jethro B-UK wrote:

AnthonyL wrote:

In 50+ years I have never seen Aperture Number as you have described and has been explained elsewhere so I don't think I've missed anything

Oh few! I thought I might have missed something fundamental.

Depending perhaps on which part of the world you come from the talk of F numbers etc may have misguided you into transposing an "f" for a  "ph"

AnthonyL wrote:

Jethro B-UK wrote:

AnthonyL wrote:

In 50+ years I have never seen Aperture Number as you have described and has been explained elsewhere so I don't think I've missed anything

Oh few! I thought I might have missed something fundamental.

Depending perhaps on which part of the world you come from the talk of F numbers etc may have misguided you into transposing an "f" for a "ph"

Pardon? I'm English BTW.

Jethro B-UK wrote:

AnthonyL wrote:

Jethro B-UK wrote:

AnthonyL wrote:

In 50+ years I have never seen Aperture Number as you have described and has been explained elsewhere so I don't think I've missed anything

Oh few! I thought I might have missed something fundamental.

Depending perhaps on which part of the world you come from the talk of F numbers etc may have misguided you into transposing an "f" for a "ph"

Pardon? I'm English BTW.

In which case you missed the point I was trying to make thatI think you meant to write "Oh phew!" and not "Oh few!", the words being a homophonic and having very different meanings.  At least in the part of England I come from

You are correct.

Oh dear, another mistake on my part.

I do know the difference between few and phew, believe me.

A 10 inch f/5 telescope has an aperture of 10 inches (254mm) and a focal length of 50 inches (1270mm). A 10 inch f/10 scope would have twice the focal length and therefore twice the magnification with the same eyepiece, but it collects the same amount of light.

It is interesting numbering, is it different than in the world of a common photography?
10 inch f/10 usually means here the lens ~250 f/10 where the first is the focal length and the latter the lens speed= maximal aperture=maximal hole the lens is capable to open to.

So I feel your example is a bit misleading, despite it is physically correct.

I mean , it is worth to mention, that the lens with the speed f/5 collects more light than the one with speed f/10 of the same focal length, when both are full open.

Jethro B-UK wrote:

You are correct.

Oh dear, another mistake on my part.

I do know the difference between few and phew, believe me.

Phew, thank heavens for that.  Now we just need to understand where this Aperture number comes from and we can sleep easy at night

Toronto Photography wrote:

i suspect that the apertue number would have made more sense if it was standard as the bigger the number seems to have more light as oppose to the denomintor of a fraction. And I suspect someone uses it just like some people use Kelvin and people used to use and maybe in the USA still use the Rankine scale.

Trivia question did white balance use the Rankine scale first then switch?

If you mean by “denominator of a fraction” the f/ stop consider this practical meaning of it:

One exposure value step ( twice more of the exposure) means for example to shift SS from 250 to 125, ISO from 100 to 200 or f-stop from f/5.6 to f/4. All the same exposure gain, 1 EV.

Do you see any aperture number on lens scale? No , because f/stop is more practical , see above.
But I appreciate curious questions anytime.

IMHO , using Celsius or Kelvin is just a tradition.