re:
http://www.luminous-landscape.com/tutorials/dof2.shtmlI know that Michael Reichmann's views are held as gospel here, but there is some bad info in the Luminous Landscape, this being some of it. Yes, focal length does affect depth of field. I think he played some slight-of-hand, saying that with the shorter focal length lens, you have to move the camera closer to the foreground subject to make it the same size as in the image with the longer focal length lens.
Well, if you're going to play that "make the foreground object the same size" game, then you have to play the "make the background object the same size" game too, by moving both the camera and the foreground subject closer to the background subject, and if you do that both will be more in focus with the shorter lens.
Or, leave the camera and all the subjects where they are, and again, both will be more in focus with the shorter lens.
Anyone who's dealt with longer focal length lenses in large format is very familiar with how longer focal lengths lose depth of field. I've worked in 8x10 and 11x14 for decades, where the "normal lenses are 300mm and 450mm, respectively.
Sorry, I had to straighten this out in another forum tonight, and thought I'd leave a note here...