Can Someone Explain Iso and Exposure?

[fwellers]

Here's one way it was explained to me, paraphrased.

It takes 3 things to bake a loaf of bread.
Heat, length of time in the oven, and the bread.

To bake a perfect loaf of bread all three things need to come together just right.
You need the right temperature
you need to keep the bread in the oven the right amount of time
And both of those things depend on the thickness and quality of the dough. ( If your dough is thinner, then you can leave the bread in the oven for less time. )


The "exposure triangle" is basically explained as above where:
the aperture ( amount of light ) is equivalent to the oven temperature ( amount of heat ),

The shutter speed ( length of time the film is exposed to the light ) is equivalent to the amount of time in the oven ( length of time the bread is exposed to the heat ),

The Iso (sensitivity of the film/sensor to light ) is equivalent to the thickness and quality of the bread itself.

All three of these things need to come together just right to get the perfect exposure. Change one, and the others must change accordingly.

Another analogy I've heard is a person sunbathing.
the sun is the aperature because it is the amount of light.
the suntan lotion used is the ISO because it affects the sensitivity of the film ( in this case, the sunbather )
the length of time spent on the beach is the shutter speed.

If you spend too much time on the beach ( same as decreasing the shutter speed ), then you will bake ( overexpose ).
To compensate for that, you can increase the amount of sunblock you put on ( same as decreasing ISO ).

That was fun.

 

[OregonAmy]

Welcome to the internet? Get used to it?

Sorry, but 6,530 of my TPF posts have been repeats of the same dozen questions, so I'm used to it.

I saw this on another forum & got a kick out of it.

http://www.googleitbitch.com/customize/

so here you go:

http://www.googleitbitch.com/old_index.php?id=975



That said, I found great explanations of ISO and exposure in [ame="http://www.amazon.com/Understanding-Exposure-Photographs-Digital-Updated/dp/0817463003/ref=pd_bbs_sr_1?ie=UTF8&s=books&qid=1228481039&sr=8-1"]this book[/ame], which I know several people have recommended.

 

[Dionysus]

ive been on the internet for almost my whole life, and a member of various forums almost the whole time, and i've never accepted that as an answer. laziness annoys me just as much in real life as it does on the internet. Ignorance annoys me just as much in both worlds as well. It's not rocket science, its just I don't understand how the switch doesnt go off in someones head when they decide to ask something, telling them "hey maybe i should search this first".

in the presence of other people more experienced than me in something, the last thing i'd want to be is the person that knows nothing of the subject. It's disrespectful to the people who came before me to not respect the "insert hobby/activity here" enough to read up about it even just a little. And it's disrespectful to the people before me who have already taken the hard road reading, learning and devoting themselves to "insert hobby/activity here"

 

[Dao]

lol ... it is human nature my friend. Basically, everywhere you go, you will see things like that. Some people go hunt for their food, some other will just open their mouth. The hunter may find the food they like, the other one may just have to eat what is being feed with. As long as both got what they want, it's all good.

 

[mrodgers]

The funniest thing to me is, people ask all the time about exposure or a specific setting like ISO, and everyone jumps in to rant in the thread about searching and how it comes up all the time.

Then someone does search, finds it impossible to get an answer because "circular polarizer" is in just about every 4 threads created on this forum, thus that someone asks a question (specific thread) and gets not one response. This person understands about the cheap brand filters vs. quality name filters which is pretty much all that was found in a search, but isn't quite sure about filters on a superzoom bridge camera or the quality of the lesser cost filters from the "good" brands and how it would affect a superzoom camera.

I guess people are too busy responding with rants on how "noobs need to learn to search" to answer the questions of others who have tried to search....

 

[Dionysus]

im not ranting on everyone else, im ranting about this particular thing. there are NO specifics to the question, nothing that sets it aside as different in any way shape or form. I think just as many people stand on their soapbox about lecturing totally new people, to fully realize HOW BASIC this question is, and its something that can be found not just here but ANYWHERE....cmon...EXPOSURE? how much more broad and wide based can you get? I can search exposure right now and find an answer to the general question on the first page. You just know how to search, which is the same as knowing what questions to ask.

I wouldnt have a problem w/ this question or others like it if there were specifics that were involved that may be different in this scenario than the others, but when its something as generic as this, and its just obvious no effort was made to look for any info, then ya i think its rant worthy.

EDIT: nice job promoting your own thread btw LOL j/k.

 

[viridari]

Forgetting the ISO setting for a moment, because you have a grasp of that, let's look at aperture vs. shutter speed.

You're in a car on the highway. You need to get from point A to point B. You can go slow and take your time. Or you can drive fast and get their quickly. Likewise with a camera you can push the aperture and shutter speed back and forth in many cases to get a different result.

Aperture is going to be like the rate of speed going down the road. Shutter speed is like the trip duration.

You can drive 120MPH from point A to point B. While you're driving and looking straight ahead, the point of focus is crisp and clear. But everything around you is just a blur.

You can drive 45MPH. Your trip duration is going to be a lot longer. But you have an opportunity to get a pretty clear view of your surroundings as you drive.

Same thing with your camera. You have to determine what effect you're going for, and juggle your aperture and shutter speed to achieve the desired result without driving past point B (aka overexposure) or stopping short of your destination (underexposure). You can use a nice wide aperture, which is like driving fast. But you'd better use a faster shutter speed. Your point of focus will be nice and clear but anything not in the narrow field of focus is going to be a blur (like the trees going by when you blow past them at 120MPH).

Or you can slow the aperture down, and use a longer shutter speed. The field of focus (or depth of field) is going to be much wider and you'll have a crisper view of more of the subject matter in the photograph, even if it's not it main subject of the image. This is like taking your time in the car driving only 45MPH.

You can take this to ridiculous extremes if you want. Or you can find a happy medium.

There is a lot of math behind this, how you can bump the ISO up or down either direction, aperture, shutter speed. So without taking a new meter reading, if you know your f/stops, you can totally change the look and feel of your image by simple shifting the balance between aperture and shutter speed.

 

[viridari]

And to the OP, if it helps to understand it, I think that "shutter speed" is a terrible term because it's not describing velocity but rather duration. Think of it like exposure duration and it might make more sense.

You might think of aperture as exposure velocity. Or maybe think of it like a tube. If you want to push water through a tube for 1/60 of a second, how much water came out the other end of the tube? You don't know unless you know the flow rate of the tube (i.e. drinking straw vs. garden hose vs. fire hose). This is aperture. The numerically lower apertures are higher flow rate (but it's flowing light, not water). So f/1.2 is like a fire hose. f/22 is like a drinking straw. f/8 is like a garden hose. Make sense? 1/60 of a second of fire hose exposure will get you a lot wetter than 1/60 of a second of garden hose exposure.

 

[prodigy2k7]

your right, but speed != velocity