Photomatix Pro version 4, made by HDRsoft, is currently the leading high dynamic range (HDR) photography software. In fact, despite the recent proliferation of competition the company is facing, Photomatix remains the beloved favorite among the vast majority of HDR photographers.
Prior to getting into a more detailed review of Photomatix Pro version 4, I will provide some basic information about HDR photography in general. In essence, a high dynamic range photo consists of multiple bracketed exposures, which have been combined in order to show details in both the highlights and shadows in a scene. Usually, it is impossible to get this amount of detail with a single exposure when shooting a medium to high contrast scene.
A good example of a high contrast scene would be a subject in a dimly lit room which is in front of bright sunlit windows. In this situation, exposing for the subject would render the windows completely blown out and devoid of detail. Likewise, exposing for the windows would render the subject very dark and poorly exposed.
There are definitely times when having parts of a scene either under or over exposed can be used for artistic effect. However, this is often not going to be the case. When we are surveying a scene with our eyes, we are constantly changing our focus and letting in varying amounts of light. So, our overall perception is that the dark and light areas do have detail. HDR photography, and specifically Photomatix, allows us to experience a photographic scene in much the same way that our eyes do.
In order to properly bracket your exposures, each one must have the same aperture, otherwise the varying depth of field will cause obvious focus issues. Most digital SLR cameras have an aperture priority setting, which makes this very easy, since it only varies the shutter speed to create the different exposures.