Not sure how to title this...i just need some help. lol.

[Pokie]

I think someone was having fun at your expense.
I didn't have time to follow the links, and all this may have already been said, but here's my piece:

F-Stop, shutter speed, and ISO all work together.
Think of them this way in regard to...tanning.

> Shutter Speed: The longer you lie out in the sun the tanner you get. Eventually you get burned. This is related to time. It's not about being faster than light, it's just about how many kazillion photons you collect. Too many is overexposure.
> F-stop = your pupils. Bright light they narrow down, dim light they open up. If you've been out tanning, your pupils get small to reduce the amount of light coming in. When you walk inside you can't see a thing. That's underexposure. Or this is why your eyes hurt when you first turn on the light in the morning, or when headlights blind you at night. Your pupils are wide open because of the dark, and the bright light all rushes in before they can adjust. It is because of the size of the opening. Too much is overexposure.
> ISO = A Swedish blonde has a high ISO and will burn quickly. It is related to sensitivity to light. Too sensitive is overexposure.

Now your camera:
Shutter speed, ISO, and F-stop all work on the doubling principle.
> Shutter Speed: Changing your shutter speed from 1/100th of a second to 1/200th of a second cuts in half the amount of light by cutting the time in half. Instead of a kazillion photons, you only get 1/2 kazillion photons. From 1/200 to 1/400 cuts it in half again. You now get 1/4 kazillion photons.
> Aperture: changing by one complete f-stop doubles or halves the open area of the lens allowing in twice as much or half as much light.
> ISO: changing the ISO from 100 to 200 means the film/sensor is twice as sensitive to light. From 200 to 100 means the film/sensor is half as sensitive.

To keep the same exposure, if you change one of these you have to adjust another in the opposite direction by the same amount.
If you double your shutter speed (slow down), you have to either cut your aperture in half or cut your ISO in half to get the same exposure.
If you open up your aperture 1 f-stop (double the open area), you either have to cut the ISO in half, or the shutter speed in half to get the same exposure.
If you double your ISO, you either have to cut your shutter speed in half or close the aperture by 1 stop to get the same exposure.
(You can also combine and adjust all three, but I'm going for the simple explanation.)

On top of this, each of these factors has certain effects on the photo besides exposure:
> Shutter speed = sharpness or blurriness of a subject in motion, also your ability to hand hold a shot and keep camera steady.
> Aperture = depth of area in focus. Wide open = narrow focus area, closed down = wide focus area. Also affects quality of optics.
> ISO = graininess or noise in picture. Higher ISO = more grain.

You might be able to use dozens of combinations of ISO, aperture, and shutter speed to get the same exposure.
But you won't get the same results. Some may be blurry because of slow shutter speed, some may be blurry because of the depth of focus/field, some may be grainy due to high ISO, etc.

Try this:

Take pictures of the same scene using the pre-settings on the camera (landscape, sports, etc.).
Then look at the picture and the settings and ask yourself - "why did the camera choose these settings?"

For sports, it probably selected a wide open aperture to collect the greatest amount of light so it could get the fattest shutter speed possible to stop the action.
For landscape, it probably selected a narrow aperture to give you the widest depth of field possible. To compensate it probably had to pick a slow shutter speed to allow enough light in (thus the reason for tripods!)

I'll stop here, got to get back to work installing a fence.

Pokie

[gldiana]

That's such a great explanation. Did you come up with it or heard it somewhere?

[Pokie]

Thanks -
The tanning example came to me on the spot with shutter speed and ISO, but had to think for a minute how to relate it to aperture.
The rest were bits and pieces I've heard, seen, or thought about before.
Kind of funny - the built in spell check didn't like "kazillion" and wanted to replace it with "bazillion".
What is the "official" definition of bazillion, 1 x 10 ^ ??

Pokie

[Traumuh]

A very large indefinite number.

[Photography~girl~]

wow. thanks pokie. that was...great.(i like how you realated it to something)
Funny though, when i wrote my essay about Aperture i used the example of the pupil. lol. Great minds think a like, eh?
And you answered an un-asked question. About when you change your shutter speed you need to then change the f/stop etc. Thanks. that is something i really don't do much. heh.
thanks again!

[gldiana]

Interesting, my post is not there or got deleted.

[Photography~girl~]

Interesting, my post is not there or got deleted.

that's odd....