Landscape Aperture Question

What is a good rule of thumb for setting aperture when one has a close foreground element and a very distant background? I see landscape photos all of the time with these elements, and I wonder how aperture was selected. If you have blowing vegetation or possible wind vibrations on the tripod, you obviously want the fastest shutter speed possible. The 350D has a function that is supposed to set aperture according to the closest and furthest elements in the frame, but I've never used it? Any advice?

The rule of thumb is the smaller the aperture (larger f/stop) the greater the depth of field - i.e 1.8 will give you a shallow DOF, f/32 will give you a large DOF. The other important part is the hyperfocal distance - the point at which you are focussing should be one third (someone correct me if I'm wrong!) of the distance into the scene to get the maximum depth of field.

For a technical explanation check out this tutorial: http://www.cambridgein​colour.com/tutorials/d​epth-of-field.htm

But also be aware of Defraction, in that below a certain apperture value (f16 -f32) the image sharpness can degrade noticably. I generally use no smaller than f16, on an APS-c sensor or f22 on my 5D (f16 is my most used landscape apperture!).

Now, see, I didn't know this:

The equations below are from David Jacobson's Lens Tutorial. MTF is the absolute value of the optical transfer function OTF (MTF = |OTF|), which includes phase and hence can go negative. The OTF for the circle of confusion C is based on a mathematical function called a Bessel function of the first kind (J1), which you won't find in simple programming languages, but which can be adequately approximated using

2 J1(x)/x ~= sinc(0.84x) where sinc(x) = sin(x)/x; below the first null of sin(x); x < π.
Let s = λ N fsp ; a = π C fsp

where λ = wavelength of light (typically 0.0005 or 0.000555 mm for green or yellow-green, near the middle of the visible spectrum; N = f-stop; fsp = spatial frequency; π = 3.14159; C = Circle of confusion. s and a are dimensionless.
For pure diffraction (no focus error; a= C = 0),
OTF(s) = 2/π (arccos(s) - s sqrt(1-s2 )) for s < 1
= 0 for s >= 1
For focus error only with circle of confusion C (no diffraction; s = 0),
OTF(a) = 2 J1(a)/a ; J1 is a first order Bessel function.
~= sin(0.84a)/(0.84a) up to the first null (0.84a < π)

Seriously, those are some good links, and I'll have to spend some time studying a little bit. I've got a holiday coming up, and I want to bring home some good photos. I may end up taking different sets of images at various apertures to be on the safe side.

And, you both have tremendous images!

I would take exile's advice - I'd use Av mode, select between f/11 and f/16 and focus approx 1/3 of the way into the scene, this will give you the max dof without any diffraction problems and in most circumstances this will be fine. Obviously the wider the lens the more dof you will get at a given aperture.

This may involve a slow shutter speed so a tripod may be needed, although an IS lens can help with this. The alternative is to up the ISO but this starts to introduce noise.