Originally posted by Wired What is the balance that is generally preferred?
For example... iso 800, F22, 1000/s
or iso 200, f22, 500/s
I'd be using a tripod... for both those examples.
I know a larger stop, the more infocus everything would be due to depth of field (correct?)
but aside from noise, is there any real reason why one would choose an iso setting over another and just use shutter speed to compensate?
Wired,
OK, here's are the basic ideas.
What you control
You control three SETTINGS on your camera: aperture (same as f-stop), shutter speed, and sensitivity or ISO. Metering mode and exposure compensation aren't "settings" in the normal sense, although they're important too.
You also control several other things that aren't "settings" but are really important factors in a good photo: the focal length of the lens; how far you stand from the subject or center of interest in the photo; where you point the camera and how you frame the shot; when you click the shutter (somewhat less obvious than you might think and worth mentioning). You control the focal length either by choosing a particular focal length prime or by adjusting your zoom. Distance from the subject is very important for depth of field. I'm going to ignore all of these (although I will come back to distance from subject).
Now, back to the settings.
Aperture
A larger aperture DECREASES depth of field - it doesn't not increase it. By "larger aperture," I am thinking literally of the open part of the aperture. F/2.8 is larger than F/16. Remember, THESE ARE FRACTIONS. 1/2 is larger than 1/16th. Depth of field isn't exactly the same thing as "focus" as you seemed to imply. Just because you use f/16 doesn't mean that you don't have to focus the camera carefully! You can have lots of depth of field - but still have the entire camera out of focus OR blurry because you didn't hold the camera still while shooting.
NOTE about aperture that it's not the sole determinant of depth of field. Focal length and especially distance from the subject really make a big difference, too. If you're shooting at 40mm from a distance of 3 ft at f/2.8, depth of field will be quite shallow: you might be able to get the person's eyes in sharp focus and have their ears somewhat blurry. Using the SAME lens and focal length and the SAME APERTURE but stepping back 15 ft, you'll have quite a bit of depth of field. So when you think "large aperture = small depth of field," keep in mind that this is relative to a given distance from the subject.
In the kind of photography that I do now (portraits and weddings), aperture is usually my first consideration, for one of two very different reasons. I shoot a lot in low light and therefore find myself needing to open up wide to f/2.8, or f/2 or f/1.8 or even f/1.4 depending on the lens I'm using, because I need to get as much ambient light as possible to take a photo at a reasonably fast shutter speed. When there's more ambient light, especially if I'm doing a formal portrait, I may have the luxury of setting aperture simply for depth of field. And if light is good, I'm not always looking for wide apertures like f/2.8: sometimes I want the opposite.
NOTE that you don't usually want to stop down much past f/11 or f/16. You get more depth of field, true, but at some point most lens begin to be harmed by
lens diffraction. Another consideration is that most lenses have a sweet spot somewhere in the middle of their aperture range. SO if you aren't primarily concerned about reducing depth of field and you just want the sharpest, clearest image possible, you will often find it somewhere around f/5.6. (This varies from lens to lens!)
Shutter speed
If the subject is static - say, a mountain landscape - and if, further, you're using a tripod, then shutter speed may not matter too much in itself. You can worry then about the aperture (for depth of field) and set the shutter to whatever it needs to be for a correct exposure.
But if the subject is moving (and the subject is ALWAYS moving slightly, unless it's a mountain), then you want a fast shutter speed to freeze movement. Sometimes it's nice to find a shutter speed that's in the middle somewhere, where you can freeze parts of the photo and not others. I took a picture last night of my dog. The dog's body wasn't moving much and the slow shutter speed (1/20th sec) was sufficient to freeze the dog's body, but not her tail - and the blurry tail is a nice effect. (
Picture here.) Usually if you're shooting sports, you want a fast shutter speed to freeze movement - say, 1/500th sec. Shooting a waterfall, the common approach is to slow the shutter speed so that the water gets a smoothed-out, flowing look.
Shutter speed can also be used to diminish the influence of camera movement. This matters mainly if you're shooting handheld, and is most important when the focal length is longer.
It's never really either one or the other
Often either aperture or shutter speed will be your FIRST consideration. But it's always important to be aware of BOTH shutter speed and aperture.
You would not want to set the aperture to f/16 for maximum depth of field and fail to notice that this meant your shutter speed was now set automatically to 1 second, because your picture will almost certainly be blurry either from subject movement or camera shake!
Conversely, if you're trying to freeze action while shooting a football game, shutter might be your first priority, but if you're too close to the action and shooting with a wide aperture, you might not have enough depth of field to get the whole line in focus as you want. But remember that distance from the subject increases depth of field for the same focal length and aperture; since you're usually shooting sports and (say) ballet from a distance, you usually have a good bit of depth of field even at your widest aperture.
ISO or sensitivity
The noise produced by high ISO photos occasionally lends an element of "mood" to a photo. But it is as close to a hard and fast rule as you get in photography that, other things being equal, you want the ISO to be as low as possible. LOW ISO = less sensitivity. Noise is not the only disadvantage of higher ISOs: more noise necessarily means less sharp details. Be aware that you can more easily ADD noise in post production than remove it. I shoot a lot between ISO 400 and 1600, in fact, the average ISO of my shots is probably around 500-600. That's because I do so much low-light photography and I don't have any choice. If I had a choice, I'd rather shoot everything at ISO 100-200.
Responding to your specific examples
You said you'd be shooting in early afternoon, and the examples you asked about all included f/22. I'd stay away from f/22 unless I had no choice. As I said above, most lenses begin to produce noticeably inferior results due to diffraction when the aperture gets very small. So increase the shutter speed. ON K10D/K20D you can go to 1/4000th sec which is pretty good for nearly any kind of shot.
The other thing you should do, if you're worried about getting the absolutely maximum depth of field, is read about
hyperfocal distance and learn how to calculate it. It's not simply the case that "f/16 produces N ft of depth of field". It depends WHERE you focus.
Hope this helps.
Will