I've been convinced. I'll explain all this now.
HDR stands for High Dynamic Range. Basically, this process involves taking several photographs of the exact same thing, ranging from very light to very dark, and then combining those exposures in a fashion so as to keep the best elements of each. This gives us a very wide (high) range of tones which we will be able to show in one image when it is finished, which produces the interesting look that HDR photos have. During the photographing process, what is being done is called bracketing. What is bracketing? Well, it is taking a series of exposures which range from light to dark (under and overexposing the image). This is often done so you have a few exposures to choose from in case something doesn't come out as you anticipated. For HDR, bracketing insures that we get properly exposed highlights, shadows, and everything in between. For example, here are the lightest and darkest exposures from one of my HDR images of the Unitarian Church.
As you can see, the first one completely blows out the windows, but the ceiling looks good, whereas the other one shows the detail of the windows but everything else is completely black. For this image I made a series of 7 exposures, in 1 stop increments, of which these are the darkest and lightest. You can adjust the number of exposures you take to fit the range you will need for the scene at hand. For sake of example, here is how the camera would have exposed the image if you had just trusted its meter and pushed the shutter button:
Once you have your set of exposures they are run through a program called Photomatix. To be fair, there are several programs to use, but this one seems to be generally accepted as the best and my experience holds to that. What Photomatix does, essentially, is to squish your range of exposures together into one image that encompasses the best of all the worlds; it uses the highlights from the dark images, the mid tones from the mid range images, and the shadows from the bright images. I won't go into a detailed account of how to use Photomatix itself, but once you are finished processing your images through it you will have a final tonemapped image. Suffice to say you make adjustments in Photomatix to get the desired effect, but here is roughly how the image looked after processing (by the way, these may not look as good as I'd like them to on your screen, but I think it gets the basic idea across):
Already, it looks much better and has a wider range of tones than any of the previous images, but generally they need further work in Photoshop. I usually do basic adjustments such as levels, color balance, saturation, and contrast, just to name a few. Then, I usually go through a process of masking in which I replace elements of the tonemapped image with elements of the other images that I prefer. For example, I may not like how the columns look, so I will just open up one of the 7 exposures where I do like the columns and replace the bad with the good using Photoshop's masking.
Anyhow, after taking the range of exposures, processing them in Photomatix, and refining them in Photoshop they are ready to go. Here is a rough approximation of the final product after all these steps:
A few notes on actually doing this:
1. Use a tripod. Any movement between exposures can result in some weird stuff. Some can be cured by the above mentioned masking process, but some of it will ruin the image.
2. Shoot in RAW format, not jpeg. Photomatix uses the extra info in RAW files to do its magic.
3. The better your camera handles noise, the better the outcome, from my experience. Darker areas will get you some noise, thus the full frame cameras seem to be a better choice here (these were done using a Nikon D3).
4. Shoot in aperture priority mode. Why? Well, because if you use Program, or something else, your aperture will vary between the individual exposures, thus your depth of field will change, alas parts of your image will be more in focus in some of the frames than the others. When you overlap this you are left with sharp and blurry over one another, resulting in something in the middle. Not exactly what we're going for.
5. While these images do not look 100% realistic, and I do not expect them to, it is very possible to go WAY over the top with them, and often it seems to happen with the saturation.
6. You will probably find that wide angle lenses are really a blessing here. This is another reason for the full frame cameras, because we can actually get 14mm out of our 14-24mm lens, whereas the smaller chips are going to cut into our wide angle of view. But, this certainly doesn't mean that you can't use any lens or any digital camera. It's all really about what you are going for. The wide angles really work for these churches, having so much in such a close proximity.
7. More exposures isn't always better. For one, the more you have the higher the chances of getting movement. I have had plenty occasions where 3 or 5 exposures came out much better than 7. So really only use as many exposures as you need to fit the range of the scene you are shooting.
8. Photomatix has the ability to process just a single RAW file instead of using a range of exposures. You can try it out and see what you get; sometimes it's cool and sometimes it isn't.
9. Finally, please do not think that the HDR process will turn a terrible photograph into a beautiful photo, because it won't. Believe me, I've tried.
Hopefully this has shed some light on what exactly is going on here. If the need should arise to explore any parts of this in more detail, then perhaps it will happen. In the meantime, if you like purple, I encourage you to visit The Purple Page. I find it relaxing.