The D90’s exposure bracketing feature is great for HDR imaging. When you turn on bracketing, 2 or 3 consecutive shots will automatically use different exposures. If you use continuous mode, simply press and hold the shutter release to take the 2 or 3 bracketed shots. The resulting shots are exactly what you need to merge into an HDR image. I used the Hydra HDR plugin with Aperture 2.1 for this one.