M5: Globular cluster in Serpens Caput


RA: 15hrs 18min 36sec   Dec: 0hrs 2min 05secs     Mag: 6   Distance: 27000 light years   Constellation: Serpens

This photo was taken on the 28th of May 2005 at f10, without any focal reduction.  21x15 second exposures were combined to provide the raw tiff file which was processed using Photoshop alone.  Histogram stretch  was more towards the dark end as increasing the brightness caused the core to become even more overexposed than it is currently.  Some slight rotational defect is visible in the outermost lying stars, but on the whole, the combination by Envisage has been quite successful.  The stretching under the Levels command in Photoshop was carried out in the RGB channel (luminosity) and the consequent brightening not only overexposed the core but also 'bleached' the colour from the yellow, orange and red stars in the cluster.  This was partially remedied by using the Curves command to enhance the yellow and red colours according to reference images.

Problem: histogram stretching should have been carried out in the individual RGB channels taking care to preserve the relative proportions of each in the raw image - this would have allowed for a truer depiction of the colours of the stars at the cluster core.

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