Hi Gordon,
For the deep-sky shots I can get away with 300 pixels per inch, and all looks fine. 300 pixels per inch also looks pretty good for terrestrial work, but as I sometimes print out images over 100 inches long [I am limited to 24 inches in width], I need to make a mosaic
All the best,
Greg
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Nexstar 11 GPS, 2 x Sky 90, M25C, MaximDL, Photshop CS3, Noel Carboni's Photoshop actions, 7 foot Pulsar fibreglass dome, Canon 40D, 100mm macro lens, 28-200mm zoom lens, 17-55mm f#2.8 zoom lens, 100-400mm zoom lens, 1.4x converter, 2x converter.
http://www.newforestobservatory.com/
http://www.flickr.com/photos/12801949@N02/