About F stops

[peter from uk]

Being a beginner in photography and reading a lot of the various

mags I often come across the words "This was taken at f3.5 or f11"

and so on. Please can anyone explain these f stops to me, are they

marked on the side of the lens? Thankyou

[markku_ylilammi]

You had better find a book about the fundamentals of photography.

Start looking for example the books of John Hedgecoe.

 

The f-numbers give the relative size of the aperture through which the light passes in the objective (lens). If the focal length is 50 mm and the f-number is 2 the aperture size is (about) 50 / 2 = 25 mm.

Therefore this number is often denoted as f:2 (where f is the symbol of the focal length). The numbers in the side of the lens are the focal length in mm and the maximum aperture size in f-number.

In (good) cameras the photographer can adjust the aperture number in

the series 1.4, 2, 2.8, 4, 5.6, 8, 11, 16 etc. and thus affect the resulting picture. Each step upwards decreases the amount of light to half.

 

The importance of the aperture size is in its effect

 

1) on the amount of light passing the lens,

 

2) in the depth of field in the picture,

 

3) on the performance of the lens (vignetting, resolution, contrast).

[anupam]

> can anyone explain these f stops to me,

> are they marked on the side of the lens?

 

Ok, if this isn't a troll ... I'd say read a book beside the mags. I have some recommendations on my webpage.

 

-A

[jcuknz]

I suggest you have a look at....

 

http://www.geocities.com/nikon5700itee/aperture_shutter.html

 

for the basics about it. There are other bits of useful basic knowledge on the site.

[jcuknz]

SORRY wrong URL try....

 

http://www.geocities.com/nikon5700itee/aperture-shutter.html

[raywei]

f-stop is derived by dividing the focal length of a lens by the diameter of the lens opening. F-stop = SQRT(2) ^ Stop Number, that's square root of 2 to the power of stop number. It starts with 1 and the next is 1.4 (sqrt(2)^1=1.414). Just remember these two numbers and then double each number you will have the whole series of f-stops, such as, 1, 2, 4, 8, 16 and 1.4, 2.8, 5.6, 11, etc. Pretty simple to remember. Have fun.

[leonard_evens]

In traditional cameras, the f-stops are shown on the barrel of the lens. There is a ring you

rotate to set the f-stop. In modern consumer grade digital cameras, the largest apert ure,

i.e., smallest f-stop number may be shown on the inside of the barrel next to the front

element of the lens, but to see the actual f-stop that is being used when you take a picture,

you have to rely on the various displays, i.e., what you see through the viewfinder or on the

LCD screen when you select the proper menu.

[jespdj]

Read this:

<p><a href="http://www.uscoles.com/fstop.htm">A Tedious Explanation of the f/stop</a>

[jcuknz]

He's right about a tedious explanation ... not a picture or graphic in site [ to pun]

[peter from uk]

Thankyou all of you, my goodness quite a complex area thats for sure!! I have read the tedious page and quite frankly I did not understand what he was going on about

[jcuknz]

Then I think you need to read Nikon5700ite's simplified page complete with graphics.

 

It is with continual amazement that I find photographers writing about a graphic subject, photography, and not using their medium to illustrate what they are trying to impart to the new chum .. personally I think it does say much for them.

 

But then Nikon5700ite used to work in the film industry so prefers pictures to words.

[jim mucklin]

Peter, confused. Simply put, the larger the number on the side of the lense( say f/16) the smaller the opening or iris in the lense. Take the lense off the camera and rotate thru the numbers. Now to confuse you more the smaller the number (say f/1.4) the bigger the opening, when they refer to wide open or the most light that particular lens will let in.

Basic photography: aperture + shutter= exposure. What's this mean to me? Well each time you move the aperture(f/stop) one number you double or cut in half the amout of light entering. The larger the number( smaller the opening, the greater the Depth of field).

Did this help?

[matthew_cole4]

If the Tedious explanation is too much, try this one: http://www.uscoles.com/technical.html

 

I don't have any photos on this page either but it is lots briefer.

[peter from uk]

Thanks again all, Jim that's the best explanation I have heard so far, now I think I can grasp it!

Just as an aside, I am buying a canon 350d or canon rebel xt in your country, what make of compactflash would you recommend, and would you go for the 512mb or 1gb I have heard that it is better to use smaller memory cards so that if it goes tits up you haven't lost all your precious photos in one swoop, like not putting all your eggs in one basket.

Once again thankyou all very much.