Ken -
Traditional HDRs combine 3 or more exposures taken by the photographer. There is a setting in every DSLR called AEB (Auto-Exposure Bracket), this setting will control the exposure level for each photo. So in the photo above, I held the camera steady long enough to get 3 photos taken (one right after the other). I typically use Av settings to do most of my HDRs, then the shutter speed will change for each exposure, but my DOF will stay the same.
Hand-held HDRs are tough. You need to stay still and sometimes one of the exposures is blurred. I highly recommend using a tripod whenever possible.
The downside to HDRs is you can do it with moving objects. You can mask certain things, but to take a photo of an airplane taxing or flying is not possible. All 3 images need to be aligned perfectly.
There is another technique called pseudo-HDRs which can be done using one RAW file. It gives interesting effects, but more often than not, the photo will not look realistic and will be filled with halos and bad colors (like the sky turning a cyan color around objects).
HDR isn't just about layering the photos on top of each other. It's about enhancing the detail of every part of the photo. There is sometimes a compromise between detail and sharpness, but detail always wins out for me. This is called tonemapping, this is what HDR software does.
I spent hours upon hours learning how to use tonemapping and HDRs. It's alot of fun to go back to old photos and see what they look like in a pseudo-HDR format. I've considered doing a write up or a tutorial on HDRs, but I don't think it would be much different then what you find else where on the internet.
If you end up trying it out, send me some samples. If you look at my Flickr page you'll see all my early HDRs, they were awful compared to what I can do now. I might be able to help you over a few hurdles and give some tips.
I use Photomatrix for my HDRs, I highly recommend it, but I admit I have not used anything else. The HDR tool in photoshop does not do what Photomatrix does. The HDR tool in CS4 is crap.
