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The Horsehead nebula in Orion, no unsharp mask

Date created: 1990-04-17

Tags: Horsehead nebula, nebula, unsharp mask, Orion

Astronomical images contain light from objects covering an enormous range of brightness, far wider than found in 'everyday' photography. Of course, in astronomy, there is no way to alter the lighting, indeed it is the light itself that is the subject of the photograph.

The photographs on these pages were made in pre-digital days, using glass plates specially designed for scientific purposes, and to capture the faintest light, rather than the beauty of the night sky. However, it was possible to control the contrast and dynamic range of the image by copying the original plates through a blurred, positive copy of the original, and this has the effect of subtly sharpening the scene and revealing detail in the brighter regions, which correspond to the blackest parts of the original plates.

All the images of the Horsehead nebula on these pages were made using a three-plate process and unsharp masks, but here we show the result of NOT using the masking process. See if you notice the difference—compare with the previous image.

Photograph made from UKST plates taken in October 1979.
Image width is about 130 arc min

Credit: David Malin

© Australian Astronomical Observatory