What Does The "f" in f/x.x stand For?

[blakers81]

In another thread, I read a post that said one of the key things to look for when taking good pictures of moving objects is a low f/x.x

I am just wondering what this stands for? And, I thought when you dish out the extra money and buy a better/stronger lens, it would have a lower f/x.x, but from checking some zoom lens, this seems not to be the case.

For instance, the Nikon D5000 I am looking at says 18-55 mm f/3.5-5.6 VG, and then another lens for it says 55-200 mm f/4-5.6 VG.

I remember reading the post about this and the poster saying that the key is to buy a camera with an f/x.x like in the 2 or 1 range.

Any thoughts on this?

Thanks.

 

[Formatted]

Smaller the F-stop the larger the aperture. Which means more light coming. So a larger F-stop the more light that can get in!

 

[blakers81]

Smaller the F-stop the larger the aperture. Which means more light coming. So a larger F-stop the more light that can get in!

Did you mean to write the SMALLER the F-stop, the more light that can come in? It sounds like you contradicted yourself in the two sentences you wrote.

 

[Formatted]

Did you mean to write the SMALLER the F-stop, the more light that can come in? It sounds like you contradicted yourself in the two sentences you wrote.

Yes I did, the smaller the F-Stop the larger opening so the more light that comes in.

It is completely confusing!

 

[blakers81]

Ok thanks.

 

[Big Mike]

F-number - Wikipedia, the free encyclopedia

The F number is a ratio between the entrance pupil of the lens, and the focal length. So when we say F8, it's actually 1:8 or 1/8 etc.

So F4 is actually 1:4 (1/4), which is physically larger than 1:8.

 

[PhotographyPool]

It's a ratio

 

[Formatted]

It's a ratio

Thanks for doing a three word post to plug your website...

 

[KmH]

The simple answer is f=1, and 1 = the focal length of the lens.
It's written that way on lenses too, 1:2.8, to denote the ratio of the lens focal length to the lens aperture that it is.

 

[WayneF]

The number value called f/stop is defined as the ratio of the lens focal length to the effective aperture diameter.

f/stop = focal length / aperture diameter.

A lens with say focal length 50 mm and an effective aperture diameter of 5 mm would be a f/10 lens aperture setting.

This beauty of this convention is that it allows the same f/stop on any two lenses, say both set at f/8, to give the same exposure, regardless of focal length.
And furthermore, we learn to know how much f/8 is.

It is commonly written as the format: f/2.8, to be remindful of the aperture diameter represented by this division of focal length by the f/number. Turns out we really don't sweat the actual diameter, this f/stop ratio number tells us what we need to know about the exposure capability.

It seems reversed until you get used to it, because of this division.

It means a large aperture diameter gives a low f/stop number (like say f/2.8, which allows more light into the exposure).

A small aperture diameter gives a high f/stop number (like say f/16, which allows much less light into the exposure).

See Photographic Tables, F/stop, Shutter Speed, ISO and EV for more detail about the details.

 

[480sparky]

It's a ratio

Thanks for doing a three word post to plug your website...

We can't?

 

[D-B-J]

It's a ratio

Thanks for doing a three word post to plug your website...

We can't?

I

 

[shefjr]

Thanks for doing a three word post to plug your website...

Zombie thread.

 

[480sparky]

Thanks for doing a three word post to plug your website...

We can't?

I

.....

 

[D-B-J]

We can't?

I

.....

Thwarted by excessive wit and sarcasm--well played sir.

Jake