The HDR mode will take pictures with different exposures automatically, so you can later combine them to make an HDR photo. This mode is based on three parameters. These are Center, EV(+-) and Frame. HDR mode takes pictures in odd numbers (3, 5 and 7). The photo in the middle of the sequence (respectively 2nd, 3rd, and 4th) will have the center exposure value. The other photos will have changing exposures starting from the lower end up to the higher end. The other exposure values are calculated with the number of stops between each frame per the total frame number.
Warning: The HDR functionality is provided with the BULB mode of the camera. The camera must be in BULB mode; otherwise, all of the photos will have the same exposure. The shutter speed you can achieve over the shutter release port is limited. In most cameras, you cannot get faster than 1/30th of a second from the cable release port. Because of this limitation, some EV(+-) and Frame values will be disabled for some Center values.