Aperture values and F Stops

[quickben]

I'm confused.

Everyone talks about f stops in apertures and shutter speeds, but I don't know what they mean. My 50 1.4 on my 10D has a range, in AV mode, of : 1.4, 1.6, 1.8, 2.0, 2.2, 2.5, 2.8, 3.2, 3.5, 4.0, etc...

What I can't my head around is when people talk about f2.8 being ONE stop faster than f4.0 ? Surely it's THREE i.e 2.8 - 3.2 - 3.5 - 4.0 ?

Please enlighten me.

Gary.

[Scottes]

One stop is either a halving or doubling of the amount of light which hits the sensor/film. The values you list are showing 1/3-stop at a time, which is one of the choices with the 10D, the other being 1/2-stop.

The full stops are: 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45
Given the same shutter speed, twice as much light hits the sensor at f/2.8 than at f/4. f/4 gives twice as much light as f/5.6, which is twice as much light as f/8.

You just happen to have the camera set at 1/3 stop increments, that's all.

You'll also find that your shutter speeds are showing 3 steps between full stops. For instance, 1/30 second is twice as much light as 1/60, right? But I bet your camera shows 3 values between 1/30 and 1/60.


Edit: Oops: There would be 2 stops between 1/30 and 1/60, or 3 stops from 1/30 to 1/60. Luckily Bob didn't catch me....

[quickben]

Thanks alot, Scottes.

I had an idea, just wanted to clarify it. Although I didn't know that one stop either way can halve or double the light. I still can't use the camera in fully manual mode. I'm scared of it :-) How do you gauge which settings to use ?

Cheers.

Gary.

[Jon]

Figure how much depth of field (DoF) you want in the picture (larger apertures give less DoF), and how fast a shutter speed you need to stop subject/camera motion, then try to find a compromise. If you can't reach a reasonable compromise, change the ISO. Or just bracket like hell.

[Scottes]

How do you gauge which settings to use ?
I shoot a lot.
:-)

I had a really big answer written and realized that this is a very tough subject. I can point you to 2 things, a book titled "Understanding Exposure" by Bryan Peterson, and an article called "Understanding Exposure" on the Luminous Landscapes web site: http://www.luminous-landscape.com/tutorials/understanding-series/understandexposure.shtml

Either will get you started abit.

[robertwgross]

How do you gauge which settings to use ?

If you ask a beginner, fresh out of photography class, what the purpose is in Aperture, the beginner will say that it balances shutter speed and ISO in the exposure calculation. That is true.

However, if you ask the experienced photographer the same question, you will get a slightly different answer. Balancing with shutter and ISO is true, but Aperture controls the depth of field, and some consider it to be a bigger purpose than exposure.

---Bob Gross---

[quickben]

Thanks for the advice, guys. That SUNNY 16 theory looks good, but I'll need a little time to be able to put into practice.

I have one question, however. Is it really any better shooting fully manual ?
Is using either, Aperture priority, or Shutter priority just as accurate (if not more) and quicker ?
In that Luminous-Landscape article, his D30 metered the scene pretty-much the way he would have done it himself.

Gary.

[Scottes]

Unless I'm using flash I shoot 99.9% of the time in either Av or Tv, mostly Av. Either of these modes, combined with Exposure Compensation, gives as much control as Manual while retaining much of the pleasure and ease of use of fully automatic.

[CyberDyneSystems]

Just to make things more confusing.. aperture value and actual f/stop are not the same..... :mrgreen: :rolleyes:

[Longwatcher]

My favorite trick is:

When in doubt set Camera on "P" take two pictures, ignore the first*, read the settings on the second, set to manual with the read settings and then adjust as needed for desired depth of field or problems with certain areas. one dial click on shutter, one on aperture, repeat as needed (Make sure custom settings have not been changed to make these different values). Change ISO from 100 only when needed.

Please note: I am more and more often getting it right from experience on the first try anyway. 5 years of digital and 40,000+ pictures later will tend to do that.


*=I never trust the first picture my D60 or 10D take. Not yet confident in 1DsMkII, but looking better.

Just my opinion and experience. Feel free to ignore.

[PacAce]

My favorite trick is:

When in doubt set Camera on "P" take two pictures, ignore the first*, read the settings on the second, set to manual with the read settings and then adjust as needed for desired depth of field or problems with certain areas. one dial click on shutter, one on aperture, repeat as needed (Make sure custom settings have not been changed to make these different values). Change ISO from 100 only when needed.

Please note: I am more and more often getting it right from experience on the first try anyway. 5 years of digital and 40,000+ pictures later will tend to do that.


*=I never trust the first picture my D60 or 10D take. Not yet confident in 1DsMkII, but looking better.

Just my opinion and experience. Feel free to ignore.

Tim, instead of switching to P and then getting the shutter and aperture settings, why wouldn't you just use the meter in the viewfinder to see what the camera would recommend for exposure (this is while you're in manual mode)? All that has to be done is set the digital needle to the center of the meter to get the "proper" exposure. You can then adjust the settings from there.

[robertwgross]

Edit: Oops: There would be 2 stops between 1/30 and 1/60, or 3 stops from 1/30 to 1/60. Luckily Bob didn't catch me....

Completely wrong. I don't know where you are going with this.

The difference between 1/30 and 1/60 is one stop, pure and simple. Or, if you want to use 1/3-stop steps, then the same difference is three steps.

---Bob Gross---

[CyberDyneSystems]

If you read the paragraph ahead of that one.. you can sort of make out what he meant..

He meant three "steps" as in adjustment steps between 1/30 and 1/60... just above Scottes says that 1/30 to 1/60 is a full "stop"

The old.. "do what he means.. not what he types". Good thing no one has any trouble understanding what I'm typing ;)

[Scottes]

Completely wrong. I don't know where you are going with this.

The difference between 1/30 and 1/60 is one stop, pure and simple. Or, if you want to use 1/3-stop steps, then the same difference is three steps.
Darnit! I knew you'd get me anyway!

My original sentence said "3 values between..." and I managed to screw up the correction by saying "stops" when I shoulda said "values" again. Grrrr.

Whatever. It's a good thing you're here to keep us accurate.

[Scottes]

Good thing no one has any trouble understanding what I'm typing
Hold on and get out the record book! Apparently you typed a full message without a single spelling mistake!

Swapping out your keyboard for a Sanskrit one is actually helping... My plans always backfire. :-)

[robertwgross]

CDS will figure it out soon. We had slipped a random key generator into his keyboard long ago. But then the way he types, he can overwhelm it and his text comes out readable.

---Bob Gross---

[Bodryn]

It may be worth adding here just as a way of clarifying the issue mathematically, that the number following the f/ is the effective diameter of the lens as a fraction of the focal length so at f/4 the aperture would be 1/4 the focal length. Since the amount of light reaching the CD or film varies as the square of the diameter of the aperture (you could think of it simply as the area of the aperture) and one stop halves or doubles the exposure, you can see that each next stop should be a diameter ratio of approximately 1.414 (square root of 2) times the diameter of the previous one. I guess this means that by common agreement over many years, "STOP" is actually a mathematical term rather than a mechanical term. I can see this may be clear as mud but it's the best I can do. :(

[Jesper]

This explains it all:

A Tedious Explanation of the f/stop (http://www.uscoles.com/fstop.htm)

[Moppie]

Who brought maths into photography?


I just know that x amount of light requires z amount of shutter speed, and y appature to get correct exposure.
I set them, take a test, check the histogram, adjust if needed, then set either apature or shutter speed to suit whats more important and adjust the other the corrosponding amount.
More apature, faster shutter and vice versa.

And I always shoot manual, unless Im to drunk.


Basicly understanding the Maths isn't important for understanding exposure.

[Tom W]

Who brought maths into photography?


I just know that x amount of light requires z amount of shutter speed, and y appature to get correct exposure.
I set them, take a test, check the histogram, adjust if needed, then set either apature or shutter speed to suit whats more important and adjust the other the corrosponding amount.
More apature, faster shutter and vice versa.

And I always shoot manual, unless Im to drunk.


Basicly understanding the Maths isn't important for understanding exposure.

Then someone comes along and introduces i, also known as ISO. ;)

[PacAce]

Every scene is lit by light of a certain exposure value. And for that particular exposure value, there are combinations of apertures and shutter speeds that will give you the correct exposure for a particular ISO.

For any given aperture, there is a specific shutter speed that needs to be used to get the proper exposure. And vice versa, for a given shutter speed, there is a specific aperture that needs to be used.

If either the shutter speed or the aperture is not right for the effect you want in the picture, then you have to either change the ISO so that you can get the right combination of aperture and shutter speed or you have to change the exposure value with the use of artificial lighting, if too dark, or neutral density filters, if too bright.

[quickben]

So I take it no-one can just walk out of their house, look at the sky, look at their subject and know exactly which exposure settings to use ?

Gary.

[Tom W]

So I take it no-one can just walk out of their house, look at the sky, look at their subject and know exactly which exposure settings to use ?

Gary.

Well, there's always the "Sunny 16" rule - that'll get you close, but there are a lot of variables that you might want to consider when shooting that can raise or lower your required exposure.

[PacAce]

So I take it no-one can just walk out of their house, look at the sky, look at their subject and know exactly which exposure settings to use ?

Gary.
Why do you say that? Pros who's life is photography, especailly nature and landscape photographers, usually have a good idea of exposure for a particular subject because they've been doing it so long. Someone (I forget who off the top of my head) posted a thread recently that pointed to a site which contains a table of EVs and the "typical" scenarios representative of that EV. Take a look at it. It's interesting stuff. :)

http://www.fredparker.com/ultexp1.htm

The chart is towards the bottom of the page.

[gramps]

Thanks alot, Scottes.

I had an idea, just wanted to clarify it. Although I didn't know that one stop either way can halve or double the light. I still can't use the camera in fully manual mode. I'm scared of it :-) How do you gauge which settings to use ?

Cheers.

Gary.
I flip a three sided coin.

[Bodryn]

And then there's always the changing amount of water vapor in the air; this is a constantly changing value, as amateur astronomers know. So one day the sky may be a clear dark blue, other days it may be much whiter in hue even though technically clear. Also the illumination of the sun is a distinct factor when at lower angular altitudes. And then if you're in the shadow of a mountain, ... Hmm, it's not so simple!

(Never bring beer to a star party!)