down and dirty of fstops

mysteryscribe

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f stops are also called aperture settings. Actually the smaller the number on the scale the larger the opening of the aperture.

Why you ask? You didn't ask? Well hell I'm gonna tell you anyway. The number are actually the demoniator of fractions. Yep f2.8 is acutally 1/2.8 or almost all of the total opening size in play. f16 is actually 1/16 or a much smaller part of the total in play.

Think of it this way would you rather have 1/16 of a million dollars or 1/2.8 of a million dollars. See now isnt that simple. There are some formulas to figure how the number are derived but I never bothered to learn them.

Remember the faucet... well it is going to come into play again. Just remember the smaller the number on the scale (or the larger the fraction) the higher the volume of light.
 
Don't forget to mention that the faction (ratio) in question is the focal length over the diameter of the aperture. So if you have a 100mm focal length, and your F stop is F4...the diameter of the aperture is 25mm.

Also, when we look at F-stops on a scale
f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, f/45, f/64, f/90, f/128...
the F numbers don't increase in a linear fashion. In other words, F8 is not twice as much light as F16. They increase by a factor of 1.414 (square root of 2).
 
So to get this straight. Do I get more light with a higher F number or a lower one?
 
exposure (light on the film) is a function of both shutter speed and fstop.... but f4 is big opening and f16 is a small opening. Thats because they are the denominators of fractions not just number. 1/16 of a pie is less then 1/4 of a pie... Ie f16 is smaller than f4... again they work inconjunction with the shutter speed which is the next bit.
 
oldnavy170 said:
So to get this straight. Do I get more light with a higher F number or a lower one?

at an identical shutter speed, there will be more light at a LOWER setting, because the hole is bigger. essentially you are getting closer and closer to a ratio of 1:1 as you open the aperture. in some lenses, if you have a depth of field previewer, you can hold it down and see the aperture close down or open to the specified setting before you take the picture.

another analogy is the principle of volumetric efficientcy in an engine. if your engine has tiny intake ports, that air will come rushing in extremely fast, but it will be so confined that not much will get in. make the port bigger, and more air can flow in, but because of reduced pressure it will be moving slower. the solution to this for an engine is simple: a giant turbo! for a photograph...............photoshop, i suppose.
 
but because of reduced pressure it will be moving slower. the solution to this for an engine is simple: a giant turbo! for a photograph...............photoshop, i suppose.

Or a higher film speed.
 
I have removed one of my lenses before and showed a couple of people
how the aperture really functions. You can cycle through the stops and actually
see how the aperture opens and closes to allow or restrict more light. I know
most of you know that... but I think some people might be afraid to tinker
with their equipment just to see how it works...
 
Remember that the funny looking "F" has always stood for 'Function' in mathematics.

A correspondence in which values of one variable determine the values of another.*

Or, simply put that whatever set of numbers that go in, can have ONE and only ONE answer.

So say a perfect exposure is a '10' Anything higher in number is over exposed, anything lower, underexposed.

What ever set of numbers of the shutter speed in relation to the aperture
must always come out the number 10 in order to make a perfect exposure. .

* http://www.google.com/search?sourceid=navclient&ie=UTF-8&rls=GGLG,GGLG:2006-25,GGLG:en&q=define%3a+function
 
I am a canon girl and I love my canon lense, my solution to this problem is to buy all of my lense with a fixed 2.8f. Problem solved. Now all I have to worry about is shutter speed, and ISO and WB and Noise and Memory and Batteries and so on and so on. LOL.
 
lorrir said:
I am a canon girl and I love my canon lense, my solution to this problem is to buy all of my lense with a fixed 2.8f. Problem solved. Now all I have to worry about is shutter speed, and ISO and WB and Noise and Memory and Batteries and so on and so on. LOL.

You are a little confused I think. Lenses that are a "fixed" 2.8, (and this only applies to zoom lenses) means that their widest aperture is 2.8, no matter what focal length you are zoomed to. If you look at the Canon 70-200 f/2.8 L, it has a maximum aperture of 2.8, whether you are zoomed to 200mm, or 70mm.

The Canon 75-300 f/3.5~5.6 has a maximum aperture of f/3.5 at the 75mm setting, but at 300mm, it has a max of f/5.6.

All lenses have a range of f/stops that they can utilize, starting from their max, whatever that may be, and, depending on the lens, a minimum of usually f/22 or f/32, and every f/stop in between.

It pays to learn them all.
 
wow. all of this sounds very confusing to me.
It took me quite some time to really figure out that basics of aperature.
And yes, taking your lens off and actually seeing what is going on is very helpful (I'm a visual learner.. which could be why I happen to love photography).
The only way that I can remember what is going on is 'A small aperature blurs the background' and I know that a small number actually means a large opening.
I read that in a book once and had it written on my hand for about 2 weeks in order to remember.

There is a topic about f-stops in beginners section and i was going to ask there what the 'f' actually stood for.

But now I know :)
 
neea said:
The only way that I can remember what is going on is 'A small aperature blurs the background' and I know that a small number actually means a large opening.

Just be careful with your terminology. A small aperture gives a large depth of field, which means a lot of the photo is in focus, with little to no blurred background.

A "wide" aperture (f/2.8) can give shallow depth of field and a blurred background.

The effect of aperture on depth of field is also influenced by focal length, and distance to subject.
 
thanks for setting me straight. I like 2.8f and stay there as a general rule. I have a 70-200L IS 2.8 and a 16-35L 2.8. I shoot alot of action in light that is constantly changing. Just makes it easier not to worry about my f stop.
 

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