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Old Oct 28, 2010, 7:33 PM   #1
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Default Aperture vs. ISO vs. Shutter Speed?

So I'm just beginning to understand these basic elements of photography (I have a Nikon D90), and my question is this: What exactly are these three things, and how do they affect the brightness of each photo?

Obviously I understand shutter speed - the number of seconds (or 1/x seconds) it takes for the shutter to open and close, and the longer it's open, the brighter the picture is going to be (aka: exposure). But the other two I don't know about, and I know they're all related somehow. So if someone could present these basic concepts in a "Layman's Terms" sort of way, I'd greatly appreciate it.
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Old Oct 28, 2010, 8:07 PM   #2
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Aperture is the size of the hole that the light travels through... A camera
lens controls aperture (the size of the hole) with multiple sliding "Blades"
that can make the hole smaller or larger...

ISO is the speed at which the film (or sensor when dealing with digital
cameras) reacts to the light that hits it...

It would take volumes to explain all of this in detail... Google can help you
find many explanations and definitions for different photography terms and
what they mean, as well as many tutorials dealing with photography...

Here's one such tutorial that you may find helps you understand photography,
Photographic terms, and how it all works...


At the end of that tutorial is a link to a page that has more tutorials... Some
basic, some more advanced...

Hope that helps...

Last edited by Wizzard0003; Oct 28, 2010 at 8:12 PM.
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Old Oct 28, 2010, 10:06 PM   #3
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One term you will hear a lot is 'stops'. One 'stop' is half or double the exposure. It is a relative term, and can be changed by any one of the three things you mention (or two, or all three, in combination). Doubling the ISO increases exposure by one stop, as does halving the shutter speed, or increasing the aperture by a factor of 1.4. (1.4 is the square root of 2, and since aperture is an area, this results in twice as much light) Increasing the aperture means using a smaller f/number, because it is a fraction.
ISO is the 'speed' of the sensor (comes from film speed). It is a measure of how sensitive it is to light.
It takes some getting used to, but if you work with it a while, it will all fall into place and become second nature.

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Old Oct 29, 2010, 7:37 AM   #4
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Brian's explanation is really of "EV," or "exposure value." When you change the exposure value by 1, it is equivalent to changing the f-stop by one (going from, say, f/5.6 to f/4), or changing the ISO from 100 to 200, or changing the shutter speed from 1/1000 to 1/500, or any combination that has an equivalent effect. "EV" is a more general term than f-stop, which is specific to change in aperture. Nonetheless, it is common in casual conversation to use "f-stop" in the way that Brian has.

Last edited by tclune; Oct 29, 2010 at 1:52 PM.
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Old Oct 29, 2010, 1:10 PM   #5
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It took me about a year to go from full auto to inderstanding a bit more how M mode works. Just recently I switched from using P mode to A mode all the time since I found how much better quality is when you stop down with apeture (ie make the apeture number bigger, like f/11 which actually makes the hole smaller)
That is one thing that is important- although the f number is bigger, it is a smaller apeture (or hole).
IMO the easy way you'll be able to learn how to use M mode is to use the other individual configs first, like ISO, and then move on to mixing them together. For an example I started with shutter speed, since it made the most sense to me-At the moment i was doing astrophotography. The longer it's open the more light will come through. Makes sense. So i messed with that, doing panning effects and fireworks and stuff; plus I knew now to watch for slower speeds. Now, with my f1.7 prime I can more fully understand how apeture works, and so I began using A mode. The time it all really made sense was when I was doing a casual indoor shoot and I had the prime wide open (smallest f number-biggest apeture-biggest hole) and I was doing a group shot. Well, when it was wide open some faces were out of focus, so I had to use a bigger f number. But then my shutter speed went down, since less light was coming in because of the smaller hole. So I had to use a higher ISO, and then it worked properly. But it all kind of came together- I was trying to find a balance between all three.
That's my little story. Hopefully you understand that you don't have to get it all at once.
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No photographer is as good as the simplest camera. ~Edward Steichen

Last edited by mrpete; Oct 29, 2010 at 8:49 PM. Reason: dumb reasoning :P
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Old Oct 29, 2010, 8:25 PM   #6
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Originally Posted by mrpete View Post
IMO the only way you'll be able to learn ...
IMHO there is never only one way to learn anything. There are many paths to a good answer, and many more to bad answers. Experiment and learn how to figure out if you have a good answer or not.
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Old Oct 29, 2010, 8:48 PM   #7
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Too true, my bad; I guess I wasn't thinking clearly. That should say "easier" . Because I do think it is the easier way, but obviously that just applies to my experience. I'll edit to fix it, hopefully before the OP reads it.
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Old Oct 29, 2010, 10:14 PM   #8
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Hi. I am just about in the same boat as you with the confusion of termonology used in digital photography. I did however learn something important you may find useful. While it seems like you could ask this type of question and get a laymans answer, even with the patient explanation from all those who answer here ( and they are all great answers), I found that the forum you might want to visit is posted in a tab at the top of the page called knowledge center. I have found, over the last week, that by researching this area almost anything I ever wanted to know about how things work in the digital field can be found there. Now what is nice about this is you can learn at your own speed, and if you are like me at all, that would be rather slow at first, and as you introduce yourself with the terms (there is actually a dictionary also), they will slowly ( or maybe faster in your case), come into focus so to speak. This has helped me because it is something I can refer to time and time again. It is a lot to learn just starting off, but as I have been told, it will not only take a lot of studying to start with, but some practical application (practice) with your favorite camera. Of course the articles keep going with subjects I was not familiar with like lighting, composition other things I know little about. It is like a gold mine just waiting for the hungry new photographer. The link Wizzard003 posted is a great starting point also (Thanks Mr Wizzard), Good luck, happy reading

Last edited by hkmp50; Oct 29, 2010 at 10:29 PM.
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Old Oct 31, 2010, 10:39 AM   #9
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Here's another way to look at it: Imagine a scene or subject you wish to photograph. If the scene or subject is brightly lit and you want a lot of detail, you might set the ISO (sensitivity) low, to around 100. If it's dim and detail isn't so important, you might set the ISO high, to around 2000. Higher ISOs usually give more noise; you can decide if that's important.

For a specific scene and ISO, there are many possible exposures. There are reasons to maybe under- or over-espose, but we'll skip those now and aim for a perfect (HA!) exposure. You point the camera and half-press the shutter and it says, 1/500 @ f/5.6. That's a specific EV (exposure value). Ah, but you can get the same EV by changing the shutter and aperture in opposite directions! Try 1/250 @ f/8, or 1/125 @ f/11, or 1/60 @ f/16. Or go the other way, 1/500 @ f/5.6, or 1/1000 @ f/4, or 1/2000 @ f/2.8.

Those different settings take the same exposure, but with different results. A faster shutter stops movement, freezes time, while a slower shutter blurs time. A narrower aperture increases the DOF, depth of field, the range that looks to be in focus, while a wider aperture thins the DOF, isolating a subject from their surroundings.

Suppose the subject is someone running at you. You set your camera with the 85/2 lens to 1/4000 @ f/2 and SNAP! and you freeze the runner, but maybe only their head and shoulders are in focus, the rest is out-of-focus (OOF). Or you set the camera to 1/30 @ f/22 and SNAP! and now everything is sharp EXCEPT the blurred runner. Same exposure, but totally different results.

Yes, ISO + shutter + aperture = exposure. That's just the starting point. Beyond that, you must decide how you want the picture to look. That's the craft of photography, where every shot is a problem to be solved in many possible ways.
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Old Nov 4, 2010, 8:51 PM   #10
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I came across this site and thought that it would help beginners....


have fun!!
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