This is a rainy day experiment - 14 exposures of M13, totalling 3 minutes and 40 seconds of exposure time (5 at 5 seconds, 5 at 15 seconds, 4 at 30 seconds) at ISO 800 were combined in Adobe Photoshop CS2 using the "Merge to HDR" function. The 5, 15 and 30 second sub-exposure groups were calibrated, registered and stacked to create three images representing the three different exposure times, then these three images were merged to create the HDR image. I think the amount of detail is striking for such a small total exposure time.

HDR stands for "High Dynamic Range". The Photoshop function attempts to create a 32-bit image retaining as much detail as possible across the total range from separate images of the same subject acquired at different exposure levels. Globular clusters like M13 are not the ideal subjects for HDR images since their dynamic range is quite limited compared to other types of objects like nebulae and galaxies - but it is a rainy day and these were the images I had with which to experiment.