I acquired 17 four minute exposures of M15 at ISO 400 on 7-Nov-2009, and combined them with 20 two minute exposures acquired last year. The result is this image, which shows deeper colors and more faint stars than my previous image of M15.

The sapphire colored star above and to the left of the cluster is HR 8231, and the topaz colored star below the cluster is BD+11 4573. The diamond-like BD+11 4578 shines just above and to the right of M15, making this object resemble a cluster of jewels.

The longer exposures in the latest set of photos resulted in the core of the cluster being washed out, but Photoshop came to the rescue, allowing me to mask the over-exposed core and let the previous, better-resolved image of the core show through.