# Aperture+Shutter Speed+ISO=Confused



## momma_morris (Oct 13, 2010)

Hello I'm new to this forum so I hope I'm posting in the right place! I've been taking pic's for a while with just a point and shoot camera, recently I purchased my first DSLR. I'd love to learn more about Aperture, Shutter Speed, ISO. I've found alot of sites just by using goggle but I'm so confused with it all! Is there a good site out there for beginning? 
Thanks,
Christina


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## Overread (Oct 13, 2010)

Understanding Exposure by Bryan Peterson 

It's a book rather than a website but its well written and idealy suited to teaching you how to start using ISO, shutter speed and apertures both to achieve a correct exposure and going further to using the settings in a creative manner.


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## MisplacedAngler (Oct 13, 2010)

What kind of photography are you into? If you're shooting mostly outdoor pics, then your ISO will typically be really low thus removing one variable from your equation and there is a direct relationship between your last two variables shutter speed and apature size.

BTW, the book Overread recommended is good, but I learned most of what was in the book online before I ever bought it.


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## edouble (Oct 13, 2010)

ISO directly affects your shutter speed. Higher ISO = faster shutter speed. There as a trade off with dslr and high ISO though. Higher ISO more noise (grain) in the picture. 

Aperature is related to the size of "hole" that light travels through to the sensor. The bigger the "hole" (smaller f number) the more light can travel to the sensor. More light going to the sensor = faster shutter speed. The smaller the aperture (large f number) less light travels to the sensor = longer shutter speed. A large aperature like f/2.8 gives a narrow depth of field (dof). A small aperture like f/22 gives you wide depth of field (dof).

DOF is used to isolate a subject like a single flower (small f number). Or DOF is used to have an entire scene in focus like a flower garden (large f mumber). 

This is a very broad subject and requires pages of text and examples to fully explain.


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## Babs (Oct 13, 2010)

Overread said:


> Understanding Exposure by Bryan Peterson



+1

I've bought that book on the basis of a recommendation from this forum, and it's great. Really well laid out, well written, and online support too (not that I've looked at that yet :blushing


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## Rekd (Oct 13, 2010)

edouble said:


> ISO directly affects your shutter speed. Higher ISO = faster shutter speed. There as a trade off with dslr and high ISO though. Higher ISO more noise (grain) in the picture.
> 
> Aperature is related to the size of "hole" that light travels through to the sensor. The bigger the "hole" (smaller f number) the more light can travel to the sensor. More light going to the sensor = faster shutter speed. The smaller the aperture (large f number) less light travels to the sensor = longer shutter speed. A large aperature like f/2.8 gives a narrow depth of field (dof). A small aperture like f/22 gives you wide depth of field (dof).
> 
> ...



What he _meant _to say was; 

If you want to stop motion use a faster shutter speed.

If it's dark out you'll want higher ISO and big aperture (small number), especially if you want to stop motion. (Hi ISO lets in more light, similar to a bigger aperture, but a high shutter speed kind of counter-acts that) The darker it is the more noise you'll get from higher ISO.

If you want to focus both near and far away, use higher aperture. If you want to focus on a very specific area and blur everything else (Depth of Focus, DOF), use a lower aperture.

I would suggest using Aperture Priority or Shutter Priority for a while to get used to how they work together. (For sports/action stuff, use shutter priority).

I'm just bustin' edouble's chops. He gave a great explanation that you may be able to understand better after a few months of shooting and getting to know your camera.


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## farmerj (Oct 13, 2010)

SLR Simulator | Simulates a digital SLR camera

try that out.


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## KmH (Oct 13, 2010)

The 3 - shutter speed - lens aperture - ISO - are inter-related and are known as the Exposure Triad.

Some call it a triangle, but that is really a poor analogy.

DSLR cameras have a built-in reflected light meter. We can center the light meter reading by adjusting one or more of the 3 parts of the exposure triad to make a properly exposed image.

In a short time we discover that once we have centered the light meter we can keep it there by adjusting any 2 of the 3 exposure triad settings. The key is that if one setting is increased, the second setting must be decreased.

As an example, if we let in more light by making the lens opening larger (larger aperture), we can get the same exposure by adjusting the shutter speed so it opens for a shorter period of time.

Another similar example would be again letting in more light with a larger lens opening (larger aperture) but adjusting the ISO so the image sensor is less sensitive to light, instead of adjusting to a faster shutter speed.

Aperture is one of the things that can affect if the foreground and background of a photo are in focus. That is known as depth-of-field, or DOF. In general, large lens openings are used to make the DOF shallow with the subject sharply focused but the foreground and background blurred. That's really good for making a portrait type photo, but not good for a landscape type photo where we want the entire photo in focus.

Shutter speed can control if things are motion blurred or not. The longer the shutter is left open, the more chance things can move while the picture is being taken.
So, if we want to take pictures of runners we use a fast shutter speed to stop the motion. For a photo of a flower arrangement made inside, we can use a much slower shutter speed because nothing in the frame is moving.

ISO is just an adjustment that adjusts how sensitive to light the image sensor is. As the ISO setting gets higher, so does the amount of electronic nosie ther is in the image. The ISO setting has a bearing on what shutter speeds you can use. As the amount of available light goes down, we can increase the ISO to keep the shutter speed the same.


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## table1349 (Oct 13, 2010)

Overread said:


> Understanding Exposure by Bryan Peterson
> 
> It's a book rather than a website but its well written and idealy suited to teaching you how to start using ISO, shutter speed and apertures both to achieve a correct exposure and going further to using the settings in a creative manner.



:thumbup::thumbup:
You can't go wrong with this book.


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## shan35mm (Oct 14, 2010)

Hi momma_morris,

My website has posts that explain the very basics for each of these topics. It might be just what your looking for to clear the confusion.

I'm not a spammer, so I won't post the address here. If you would like the address, just send me a message and I will send it over to you.


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## prodigy2k7 (Oct 14, 2010)

Ugh better read the websites and books, found 2 errors is what people said above.. 95% correct though


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## prodigy2k7 (Oct 14, 2010)

edouble said:


> *ISO directly affects your shutter speed.* Higher ISO = faster shutter speed.



No. Changing your ISO only under or over exposes your photo. You compensate with changing aperture or shutter speed. For example: If you are in Tv mode, you are set to 1/500 and you change your ISO from 100 to 200, your aperture changes, not your shutter.




Rekd said:


> If it's dark out you'll want higher ISO and big aperture (small number), especially if you want to stop motion. (*Hi ISO lets in more light*, similar to a bigger aperture, but a high shutter speed kind of counter-acts that) The darker it is the more noise you'll get from higher ISO.


This is a little misleading. A higher ISO can seem to give the photo more light exposure physically but no more light is actually entering the lens. Im pretty sure you already know this but want to clear that up for readers. ISO simply amplifies the signal the signal. The sensor receives the same amount of light depending on the shutter and aperture only.


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## edouble (Oct 14, 2010)

prodigy2k7 said:


> edouble said:
> 
> 
> > *ISO directly affects your shutter speed.* Higher ISO = faster shutter speed.
> ...




Wow, that is the most absurd definition of ISO that I have ever heard. "ISO only under or over exposes your photo" - wrong wrong wrong wrong!!!! Changing ISO increases or decreases the sensitivity of the camera's sensor. Increasing or decreasing this sensitivity directly affects shutter speed.

Is you shoot in a shutter priority mode then yes the aperature would change. A high ISO is 99.9999% of the time used for faster shutter speeds.

Know what you are talking about before you tell others they are wrong ldman:

From wikipedia "*Film speed* is the measure of a photographic film's sensitivity to light, determined by sensitometry  and measured on various numerical scales, the most recent being the ISO  system. Relatively insensitive film, with a correspondingly lower speed  index requires more exposure to light to produce the same image density as a more sensitive film, and is thus commonly termed a _slow film_. Highly sensitive films are correspondingly termed _fast films_.  A closely related ISO system is used to measure the sensitivity of  digital imaging systems. In both digital and film photography, the  reduction of exposure corresponding to use of higher sensitivities  generally leads to reduced image quality (via coarser film grainimage noise of other types). Basically, the higher the film speed, the worse the photo quality." or higher


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## Proteus617 (Oct 14, 2010)

This stuff gets easier if you think of it in terms of "stops".
Aperture (F-stop) relates to the size of the iris in the lens
Speed is the shutter speed
ISO is the sensitivity of the film

Here's the sequence 
F-stop: 1  1.4  2  2.4  4  5.8  8  11....
Speed: 1sec  1/2  1/4   1/8  1/15  1/30...
ISO:  3200 1600 800 400 200 100...

Don't worry about the above numbers, think of them as units on a number line.   Each unit is one stop apart.  On any of the three scales, moving one number to the left doubles your sensitivity to light, one number to the right halves it.

For example: your camera is in auto and suggests ISO 100, F8, 1/100.  Want to increase your exposure one stop?  Move any one of those values one stop to the left.  Want to open up your aperture to F4 but keep the exposure the same?  F8 to F4 is +2 stops. so you have to change your shutter speed or ISO -2 stops to compensate.


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## RSPhotography (Oct 14, 2010)

wow, there are so many wrong definitions of ISO on this thread!!

it's not surprising you're confused because it appear's that lots of others are too!!

Did you ever have a film camera? If you did then you may remember that you could purchase film with different ISO numbers. They referred to how sensitive the film was to light. The higher the number, the less light was needed to 'expose' a photograph.

The same applies to digital. Your DSLR has a sensor in it that reacts to light. The sensor is actually analog (i.e. not digital) and you can increasse or decrease the sensitivity (gain) by adjusting the ISO number.
generally you want the lowest number you can afford as increasing the number adds more noise to the picture. (Think of 'gain' as volume - you increase the sound but you also increase the background noise)

However, most of the time you'll have to increase the ISO speed in order to capture enough light.

I think aperture and shutter speed have been covered rather well... (aperture = size of hole, shutter speed = length of time the shutter is open to capture a pic)


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## Overread (Oct 14, 2010)

Overread said:


> Understanding Exposure by Bryan Peterson



I think a few more people in the thread need to get and read this book


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## GeneralBenson (Oct 14, 2010)

Overread said:


> Overread said:
> 
> 
> > Understanding Exposure by Bryan Peterson
> ...



Indeed. The thread should have been locked as soon as you answered correctly by saying, go read that book. After that there is nothing left to say, and so far everything else has just lead to more confusion.


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## prodigy2k7 (Oct 14, 2010)

edouble said:


> prodigy2k7 said:
> 
> 
> > edouble said:
> ...



A higher ISO allows you to use a faster shutter speed, but it also allows you to change the aperture instead. Sure most people use higher ISO for faster shutter speeds, its very common, that doesnt mean ISO directly influences it. It doesn't. And YES your photo will become under or over exposed if you are in MANUAL mode, dont change your aperture/shutter and change your ISO.

Edit: I was talking about the end result if you change your ISO without changing your aperture/shutter, yes the ISO is the sensitivity to light, but the end result is, under or overexposure of your photo, if you don't compensate. Yes its most common to change shutter speed, but you are acting like its friggin physics, and it MUST change the shutter speed, like its a science. Its not. You are just confusing the guy more. I wasn't defining ISO. I said exactly what it DOES (in the eyes of the person) not the technical stuff...


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## iskoos (Oct 14, 2010)

If a male newbie asked this question, he would get immediate advises on how to use the "search" function...

This forum is full of info about what you are asking. You do not need to buy a book immediately. Go to "Beginner's Photography" forum and type Aperture, shutter speed, ISO or simple "Exposure Triangle", and you will find lot more than you may expect.
I remember some members even started tutorial threads with sample pictures...


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## icassell (Oct 14, 2010)

Overread said:


> Understanding Exposure by Bryan Peterson
> 
> It's a book rather than a website but its well written and idealy suited to teaching you how to start using ISO, shutter speed and apertures both to achieve a correct exposure and going further to using the settings in a creative manner.



:thumbup::thumbup::thumbup:


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## ghpham (Oct 15, 2010)

If I was a newbie, I wouldn't understand what half of you guys are saying.  Recommending the book is about the best advice.


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## RSPhotography (Oct 15, 2010)

I dunno...
They're fairly simple concepts. Not sure there's a need to spend any money to understand them!

... just my opinion!


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## Rosshole (Oct 15, 2010)

ISO - this part determines how much light is needed to expose an image

Shutter speed - Determines how long light will be hitting the sensor

Aperature - How much light is let in when the shutter is open

Changes to each inversly effect the other two, and making changes to them will give you different effects on the exposure...   ie, Frozen motion, depth of field, motion blur.

That's it.


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## table1349 (Oct 15, 2010)

RSPhotography said:


> I dunno...
> They're fairly simple concepts. Not sure there's a need to spend any money to understand them!
> 
> ... just my opinion!



Which is why Bryan Peterson wrote his book on Understanding Exposure and Ansel Adams wrote about the Zone System.  The concept seems simple, however the application, given the physics of photography, is not.


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## Dao (Oct 16, 2010)

I think one important point a beginner need to know is....

A photographer, most of the time, want to take a photo with "CORRECT EXPOSURE".  Such as take a photo that it does not look too bright or too dark.  There are exceptions of course.



How to obtain the "correct exposure", it is a combination of setting the "Aperture", "Shutter speed" and ISO/ASA (which is kind of like a light sensitivity value).


If correct exposure is 1 bucket of water.

To fill 1 bucket of water, I need to use a hose.  Of course with a bigger hose (larger aperture),  I can fill the bucket faster.  Therefore I only need 20 seconds (Shutter speed) to fill the bucket.

Now, I can only use the smaller hose (smaller aperture) since the big one broke.  To fill the same bucket, now it take 40 seconds. (double the shutter speed).

The problem is, I need to fill one bucket in 20 seconds, 40 seconds is too slow.  To solve the problem, I use a smaller bucket (ISO/ASA) which is half the size.


The end result is the same, I have 1 bucket of water (correctly exposed photo)

Hope that make sense.


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## bentcountershaft (Oct 16, 2010)

icassell said:


> Overread said:
> 
> 
> > Understanding Exposure by Bryan Peterson
> ...



The nice thing about that book is that it has photo examples of the same scene so that you can see how each of the variables affect an image independently.  Seeing those images side by side really makes it easy to understand exactly what is going on in a picture and how to adjust to get the effect you want.  For me as beginner it felt like an epiphany learning that and that book made it easy.  It's been out a good while and is probably available at the local library if you don't want to buy it but it's really nice to have.  I'd be willing to bet it's the single most recommend book on photography out there and for good reason.  It's easy to understand even for someone that has never picked up a camera before.


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