I don't understand what ISO settings are and how that affects pictures. I also noticed people say they shoot some pics in f2.8. What does that mean. I have a p&s camera, but I can adjust those settings some in manual mode. Any explanation would be greatly appreciated. TIA

 

shutter speed, iso, and aperture are all correlated with one another. you will hear the 'stop' quite often when people talk about these three settings. if you're good at math, it's easy to figure out.

when talking about aperture, going from 2.8 to 4.0 is worth one stop less light. If you go from 4.0 to 2.8, you let one more stop of light in. the same can be said about shutter speeds and iso. For iso, going from 100 to 200 is the equivalent of one f/stop. Also, going from 1/30 to 1/60 is worth one stop of light.

aperture goes as follows:
1, 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, etc

shutter speeds:
1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, 1/2000, 1/4000, 1/8000

iso:
50, 100, 200, 400, 800, 1600, 3200, 6400

You can toss in 1/2 stops or 1/3 stops but that'll just confuse you so I'll stick with the full stops.

To put it in real terms:
you expose a scene and use these current settings:
ISO 100, f/2.8, 1/60

With the above settings, the scene is exposed properly but you want to change your shutter speed from 2.8 to 4.0 to increase your depth of field. To keep the scene properly exposed, you'll either have to change your ISO from 100 to 200 *or* go with a slower shutter speed of 1/30. By going from ISO 100 to 200, you allow one additional stop of light. By going from 1/60 to 1/30 shutter speed, you also allow 1 additional stop of light.

Now, let's say you want a faster shutter speed of 1/125. Since the shutter is open for a shorter duration, you need more light to properly expose the image. You either have to stop down from f/2.8 to f/2.0 *or* change the ISO from 100 to 200. You can also change settings in 1/2 or 1/3 stops but I'll keep it simple and stick with full stops.

Confused yet?

 

in film, ISO is the measure of the sensitivity of the film to light. Essentially, a 100 ISO film takes twice as long to expose properly in the same light as a 200 ISO film, given the same aperture, or f-stop. ISO in digital cameras is an approximation of this system.

F-stops, like f2.8, are a way of controlling the amount of light that hits the film, along with shutter speed. For a given shutter speed, going from 2.8 to 4 doubles the amount of light that hits the film. It actually describes the aperture, or hole that lets light through when the shutter is open, in a ratio of lens length to aperture size. You usually seen aperture written as f/2.8 or f/4. Given the physics of light, f/4 is half the size of f/2.8, which is half the size of f/2.

So as long as the light doesn't change, you get the same exposure at 1/500 @ f/2 as at 1/250 @ f/2.8, and 1/125 @ f/4. That doesn't mean the pictures will be the same, however. The area that is in focus will be smaller at f/2 than at f/4, so more of the foreground and background will be out of focus at f/2. It is common to use this behavior to isolate the subject using a wider aperture, i.e. the subject is the only thing in the photo in focus. The farther you are from the point of focus (the subject in most cases), the deeper the depth of field. So if you are close to the subject and use a wide aperture, you can easily blur the background. Conversely, if you are farther from the subject, the region of focus is deeper.

 

I almost think these lessons are done and not read. This is one of the best explanations of exposure controls I've ever read , but I can certainly see where an exposure newb would be so lost with that post.

Again, awesome explanation

 

one minor typo - "stop down from f/2.8 to f/2.0"

Going from f/2.8 to f/2 is opening up, not stopping down. "Stopping down" is going to a smaller aperture.
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In general, set the ISO at the lowest you can and still have a usable shutter speed. For stationary objects when using a tripod, this is easy, but for handheld shots and/or for living things, it gets a bit more complicated. But basically, if you are going for the sharpest image with the largest depth of field to get everything in focus, set the camera at say, f/8, and if your shutter speed is too slow to avoid blur you increase ISO until you get a fast enough shutter speed. Faster is better, but you lose image quality if you shoot at 1/1000 at ISO 3200 instead of 1/60 at ISO 200.

As the focal length increases, you need a faster shutter for handheld and/or possibly moving subjects (like people). A general rule of thumb is 1/focal length is the slowest shutter speed for handheld shots to avoid camera shake. So for a 50mm lens, 1/50th or faster. If your subjects are not standing still, you probably want a faster shutter to stop movement. It takes trial and error to figure out the ideal shutter for a given situation.

Another thing to think about is all apertures aren't the same. Most lenses aren't sharpest wide open or stopped down all the way. Most lenses perform best between f/4 and f/8, give or take a stop. So you generally have three to five aperture/shutter combinations for best sharpness at each ISO. It's generally considered better to get the shot than not, so don't worry too much about the ISO as long as you can eliminate camera shake or subject blur, and don't worry too much about whether you are using the best aperture for sharpness. If you have to use your smallest aperture, it is better to go to a lower ISO instead, and by the same token, if you need your widest aperture, feel free to move to a faster ISO.

There is a lot more to photography than pointing and shooting, which is why P&S cameras are so popular.

 

Get the 17$ book, Understanding Exporsure by Bryan Peterson, it's the best thing you can do to understand photography, etc.

 

http://www.camerasinteractive.com/index.php#

Click on the virtual camera link on the right and follow the tutorial.

It will explain both your questions and give you graphic examples.

Hope it helps.

 

Thanks vrey much for that. It was great! learned a lot!!!

 

Personally I'd forget about ISO and concerntrate on aperture and shutter first - they relate directly to each other.

ISO is confusing the issue in my opinion. Once you're happy with how aperture and shutter work, then by all means consider film speed (or the digital equivalent in this case) but I wouldn't use it as a compensation tool for light unless you've exhausted all other options (wide aperture, slow shutter, tripod etc etc).

 

When you know what you are doing with shutter and aperture as Badger says, then you can have fun with ISO speed.

It's one of the great things about Digital that you can change the film speed with every shot, it's like putting different film in the camera for every shot but as Graham says it's confusing to those new to the medium.

Some of the best advice on settings that was ever published was the settings advice you got on the side of old fashioned Kodak film boxes

Sunny day 100 ASA (I am old ) (== ISO 100) 1/125th of a second at f16 with the sun behind you and your shots will always look good (be correctly exposed).

The sun is a pretty standard candle