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By combining a multitude of frames of deep sky objects, it's always very rewarding to witnessing how faint galaxies in deep sky objects emerge above the noise levels. Above are two images of the Abell2218 galaxy cluster. This cluster contains some 10000 galaxies and is located at 719 Mpc from us. The left image shows a composite RGB image taken with the Hubble Space Telescope. Rings have been added around cluster members from the brightest to the faintest objects (of mag >22). The same objects are visible in a Luminance stacked observation taken by a group of students at UCLO who created our own "Deep Field" by "stacking" many tens of frames (for an approximate integration of over 3.5 hours) from one of our C14s.
The stacking of multiple frames with limited integration time, allows us to minimize the impact of spurious features (plane or satellite trails) and reduce the impact of sky background to obtain relatively high magnitude limits.