HDR photos - some finer points

I am sure you have all read the tutorials, and know the basics of HDR photography. A good steady tripod, the camera set to aperture-priority, a range of different apertures, preferably taken automatically to minimise any movement, and hence 'ghosts' in your picture. Reading the posts on the different discussion forums, you will be advised by one person to always take 5 separately-spaced photos, whilst another will advise 7 or even 9. Some will say that 3 photos, spaced at 2ev, are sufficient. Who is right?

I'd like to suggest that to answer this question, you think a little about the REASON for taking a range of photos. We are trying to capture a high dynamic range such that all aspects of the photograph, from the darkest shadow to the lightest bit of sky, are correctly exposed. To combine these images, the Photomatix, Picturenaut, or whichever software, needs the raw data to work on. The software can't do something magical, and create data that isn't there. It is easy to stand in awe of the software, to give it the photos you assume it needs, then expect it to turn out a masterpiece. Sometimes it can, but often it doesn't, and one of the reasons that this happens is because the software didn't have a suitable range of light to start with.

So, instead of automatically setting your camera to 5, 7, or whatever number of images you are used to, I would suggest taking a little time to ensure that the data needed is really captured. Take a test image at the correct exposure, then examine the screen to see the range of light and dark in the scene. Determine the correct exposure to bring out the detail in the darkest area. Determine the correct exposure to bring out the detail in the lightest area. It is only when you have done that will you then know the range of exposure needed for the scene. Divide this range into 1-ev increments, and you will know how many shots you need to auto-bracket. Do this and you will never again be disappointed by a lack of detail in a dark or light area of your image.